mOSCOPY 
 
THE LIBRARY 
 
 OF 
 
 THE UNIVERSITY 
 OF CALIFORNIA 
 
 PRESENTED BY 
 
 PROF. CHARLES A. KOFOID AND 
 MRS. PRUDENCE W. KOFOID 
 
 Mailed Abroad Free. 
 
 HENRY CROUCH, 66, Barbican, London, E.G. 
 
MEDALS AND HIGHEST AWARDS 
 
 London, Paris, Philadelphia, l^BSfc. Antwerp, Sydney, &c^ 
 
 ROSS' 
 
 IMPROVED 
 
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MICROSCOPES. 
 
 R. & J. BECK, 
 
 ESTABLISHED NEARLY 50 YEARS, 
 
 HAVE DEVOTED GREAT CARE AND ATTENTION 
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 ACHROMATIC MICROSCOPES 
 
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 TASTE AND REQUIREMENTS OF PURCHASERS, 
 
 WHETHER STUDENTS, 
 PROFESSIONAL MEN, OR AMATEURS. 
 
 THEIR STUDENTS' MICROSCOPES 
 
 ARE THE CHEAPEST MADE, COMBINING LOW PRICE WITH 
 EXCELLENT WORKMANSHIP. 
 
 And the quality of the "Economic" Object Glasses is such thgt the 
 higher powers will resolve most of the difficult Diatomaceous 
 
 Tests, and meet the wants of Medical Students, 
 By their Fine Correction, Superior Definition and Penetration. 
 
 PRICE FROM 1 TO 10 10s. 
 
 THEIR FIRST-CLASS STANDS ARE OF THE MOST COMPLETE CONSTRUCTION. 
 "VIDE" INTERNATIONAL MICROSCOPE ILLUSTRATED IN THIS VOLUME. 
 
 COMPLETE ILLUSTRATED CATALOGUE, Price 2s. 6d. 
 
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NTISPIEC 
 
 ~f<*s 
 
 
 EUCALYPTUS GLOBULES 
 
 WOOD SECTIONS DOUBLE STAINED 
 
 CHAP. XU. 
 
PRACTICAL MICROSCOPY. 
 
 BY 
 
 GEORGE E. DAVIS, 
 
 F.R.M.S., F.I.C., F.C.S., 
 
 ETC., ETC. 
 
 ILLUSTRATED WITH TWO HUNDRED AND FIFTY-SEVEN WOODCUTS 
 AND A COLOURED FRONTISPIECE. 
 
 LONDON: 
 DAVID BOGUE, 3 ST. MARTIN'S PLACE, 
 
 TRAFALGAR SQUARE, W.C. 
 1882. 
 
PREFACE. 
 
 THE Author's object in presenting this work to the student 
 of microscopy is to supply at a reasonable cost a book 
 written upon somewhat similar lines to Quekett's ' Prac- 
 tical Treatise on the Use of the Microscope,' the second 
 and last edition of which appeared in 1852. The necessity 
 of a treatise bringing the science to the present day has 
 been long felt, and it is hoped that a vacant place in micro- 
 scopical literature is now filled up. 
 
 Although essentially a practical work upon microscopy, 
 the reader is treated to a little theory, in the hope that it 
 may lead to a more minute study of the optical principles 
 upon which the microscope is constructed. Some may 
 object, perhaps, to so little theory being introduced, espe- 
 cially on those subjects intimately connected with Professor 
 Abbe's recent researches ; but it should be remembered that 
 the addition of such matter would have added considerably 
 to the cost of production and detracted somewhat from the 
 practical character of the book : this, taken together with 
 the fact that ample references have been given to Professor 
 Abbe's papers, will, it is hoped, be sufficient apology. 
 Moreover, the information lately put forth is novel to the 
 
 general body of microscopists ; the views now held are so 
 
 a 2 
 
IV PREFACE. 
 
 decidedly opposite to those promulgated but a few years 
 ago, that it is evident any one writing on the subject now 
 could only put forth an abstract of the learned Professor's 
 views. This the Author did not wish to attempt, as such a 
 proceeding would only have mystified the student, and not 
 have furnished the advanced worker with as much informa- 
 tion as he could obtain from the 'Journal of the Royal 
 Microscopical Society,' where Professor Abbe's papers may 
 be found in extenso. 
 
 With regard to the selection of objectives, the Author 
 hopes he will not be misunderstood : medium angles have 
 been advised for students' use, for the simple reason that 
 they can be employed without much previous knowledge 
 or difficulty ; but for all purposes of scientific investigation, 
 wide apertures, requiring often much skill in manipulation, 
 will give the most satisfactory results. 
 
 Our American brethren have for many years been im- 
 pressed with the importance of wide apertures, and no 
 doubt many of their arguments were sound, though it can- 
 not be said that their case was ever well demonstrated and 
 supported. 
 
 Dr. G. E. Blackham, in a paper read before the Micro- 
 scopical Congress at Indianapolis in 1878, argued ex- 
 clusively for wide apertures, though he was singularly 
 unfortunate in his selection of a theory to account for 
 "penetration" in objectives; while this brochure has been 
 supplemented by a volume from the pen of Professor J. E. 
 Smith, ' How to See with the Microscope/ putting forward 
 again the merits of wide angles. 
 
 Microscopists who have read these works will do well 
 
PREFACE. 
 
 to study what Professor Abbe has written, and then they 
 will probably come to the conclusion that the high-angle 
 school possess some forcible arguments, and may also 
 find that with wide apertures their battery of objectives 
 
 may be considerably smaller to accomplish work of a better 
 
 
 
 quality than when low angles are employed. 
 
 Under the head of objectives, the almost total absence 
 of American productions will be remarked : it is only 
 recently that American objectives of the widest aperture 
 have found their way into the Author's hands. Their 
 definition is marvellous, but it has not been thought 
 advisable to include such objectives in a practical work 
 until after they have been used in ordinary observation for 
 a sufficient length of time. 
 
 However, the reader may like to know that Spencer, of 
 Geneva, U.S.A., produces a 3-inch of I3,*a 2-inch of 20, 
 and a i-inch of 50; while Tolles, of Boston, U.S.A., makes 
 similar objectives, a ^ of 145; both of these opticians pro- 
 ducing the J-inch and all higher powers, of 180 air-angle. 
 
 These wide apertures demonstrate clearly the accuracy 
 of the statement made on page 5 1, that wide angles require 
 more care in their correction, and are consequently more 
 expensive. Spencer's i-inch of 50 costs forty-five dollars, 
 or 9/. ; while the i-inch of 22 in their student's series costs 
 but ten dollars, or 2/. 
 
 The whole of the information in the work has been 
 selected to aid the student as much as possible ; but it 
 should be remembered that the microscope is useful, from a 
 scientific point of view, only as an aid in research, unfolding 
 to us objects either invisible, or but faintly to be distinguished 
 
vi PREFACE. 
 
 by the unassisted eye. The Author has not pandered to the 
 tastes of mere lovers of pretty objects. 
 
 As to the preparation and mounting of objects much 
 more might have been said ; indeed, volumes written on 
 this subject alone ; but types have been selected to avoid 
 repetition, and which the student will do well to follow. 
 All the processes in practical microscopy must be carried 
 out with intelligence, and the why and the wherefore of 
 each well understood. If this be done the student will 
 find no insuperable difficulties. 
 
 Many of the illustrations found herein have been photo- 
 graphed from nature by the Author, and cut in the en- 
 graving department of 'Design and Work,' and thanks are 
 here expressed to the proprietor for these blocks, which have 
 enabled the work to be so fully illustrated at a moderate 
 cost. To the publisher of 'Science-Gossip/ for similar 
 reasons, thanks are likewise expressed. Many of the illus- 
 trations have been lent from the ' Northern Microscopist.' 
 
 In conclusion, the Author asks his readers to communi- 
 cate to him, under care of the publisher, any ideas or 
 suggestions in view of future editions, and hopes he has 
 established a sufficient raison d'etre. 
 
 GEORGE E. DAVIS. 
 
CONTENTS. 
 
 CHAPTER I. 
 
 PAGE 
 
 INTRODUCTION .... i 
 
 CHAPTER II. 
 
 THE MICROSCOPE STAND 
 
 CHAPTER III. 
 EYE-PIECES AND OBJECTIVES 40 
 
 CHAPTER IV. 
 ACCESSORIES 58 
 
 CHAPTER V. 
 
 GENERAL REMARKS UPON OBJECTIVES TEST OBJECTS .. 97 
 
 CHAPTER VI. 
 
 THE COLLECTION OF OBJECTS 127 
 
 CHAPTER VII. 
 
 MICRO-DISSECTIONS ! 
 
CONTENTS. 
 
 CHAPTER VIII. 
 
 PAGE 
 
 SECTION-CUTTING .. 182 
 
 CHAPTER IX. 
 
 THE DELINEATION OF OBJECTS MICROSCOPIC MEASURE- 
 MENTS 203 
 
 CHAPTER X. 
 THE POLARISCOPE 238 
 
 CHAPTER XL 
 THE MICROSPECTROSCOPE .. .. 249 
 
 CHAPTER XII. 
 STAINING AND INJECTING ,.'->....).. .. 259 
 
 CHAPTER XIII. 
 THE PREPARATION AND MOUNTING OF OBJECTS 271 
 
 CHAPTER XIV. 
 REAGENTS RECIPES 312 
 
 INDEX 325 
 
PRACTICAL MICROSCOPY. 
 
 CHAPTER I. 
 INTRODUCTION. 
 
 DURING the past few years rapid strides have been made in 
 the manufacture and supply of cheap and at the same time 
 really good working microscopes ; and these having been 
 extensively purchased, have extended and disseminated a 
 taste for the study of minute things, in those to whom the 
 possession of a microscope a few years ago seemed a luxury 
 to be only dreamt of. 
 
 Good works treating upon the practical use of the 
 microscope and its accessories, have hitherto been of so 
 expensive a character as to be certainly beyond the reach 
 of most students, and many who might have been led 
 into the paths of scientific research, have probably kept 
 their instruments to gratify the curiosity of themselves and 
 their friends. Such persons often think that the possession 
 of a microscope must always make a microscopist, and in 
 order to study objects, that it is only necessary to place 
 them on the stage of the microscope when their hidden 
 structure will manifest itself at once. No greater mistake 
 could ever be made. It is very desirable that the student 
 should be thoroughly acquainted with the physics and 
 chemistry of the science, for when once these are mastered 
 
 B 
 
PRACTICAL MICROSCOPY. 
 
 he will see his way to carry on experiments in a rational 
 manner, as often as fresh problems are presented to him. 
 
 Again, no inexpensive work upon practical microscopy 
 brings the subject down to the present time ; this and 
 other minor details urged us to cut out a path for our- 
 selves, and produce a treatise which might be of use to the 
 student. 
 
 In using the microscope as a means of gaining an insight 
 into the anatomy or life-history of forms only faintly dis- 
 tinguished by the unassisted eye, the student must be 
 prepared to exercise a certain amount of patience ; skill in 
 manipulation comes by practice only, and before com- 
 mencing with any investigation, all preconceived notions 
 should be cast aside, the observer being guided chiefly by 
 the results of his own observations. 
 
 Isolated observations should never be considered con- 
 clusive ; experiments require frequent repetition under very 
 varying conditions before we can accept the results as true 
 interpretations of what we have actually seen. We should 
 also be careful to take into account the degree of per- 
 fection of our instruments as well as our own capability 
 of vision ; what one observer will see, another will fail 
 to detect, and if any preconceived notions exist, the 
 observations are sure to be moulded after the same 
 fashion. 
 
 Expertness in microscopy is only to be attained by study 
 and practice, and as it is necessary, in order to progress, 
 that we take up the subject where our predecessors left off, 
 it is necessary to become acquainted with what has been 
 done previously, and this may be arrived at by the perusal 
 of old standard works upon the science, such as those of 
 Baker, Pritchard, and Goring, or the more recent work of 
 Mr. Quekett's, ' The Practical Treatise on the Use of the 
 Microscope.' These works, though old, are valuable, and 
 
INTRODUCTION. 
 
 the executive of every microscopical society should en- 
 deavour to secure a copy of each for its library. 
 
 If microscopical students would only peruse these older 
 works, and enter into communication and discussion with 
 their brother microscopists, much time and work would be 
 saved, and a great deal of that re-discovery which goes on 
 at the present day averted ; there is no other way of 
 avoiding repetitions except by the methods above stated. 
 
 We might advance more rapidly, or more certainly at 
 least, if we asked, before performing any microscopical 
 operation, the reason why. We are too apt to do things 
 in a certain manner because some one who instructed us 
 in the art and mystery did so before us ; no inquiry was 
 made, but we did likewise. If the principles upon which all 
 operations are conducted were thoroughly understood by 
 all those who intend working with the microscope, much 
 labour would be saved, needless experiments avoided, slides 
 rendered more permanent, and microscopical research 
 brought more into favour on account of some of the barriers 
 which now obstruct progress having been broken down. 
 
 It is in this direction that a treatise may be useful to the 
 student ; objects themselves, whether of animal, vegetable, 
 or mineral origin, are best treated of in works entirely 
 independent of practical microscopy; an organism, how- 
 ever minute, has its life-history, and it should be the aim 
 of each student to be useful in his generation by endeavour- 
 ing to furnish an accurate account of the cycle of existence 
 of some member of the animal or the vegetable world. 
 
 Of course, before he can be expected to occupy himself 
 with original research, he should be fairly acquainted with 
 all that has been done before upon the subject ; but above 
 all must he be familiar with the instrument with which he 
 works, and the methods whereby certain results may be 
 
 attained. 
 
 B 2 
 
PRACTICAL MICROSCOPY. 
 
 Microscopical research does not always require the aid 
 of expensive apparatus. It is very handy and often saves 
 time, no doubt, to have ready all those accessories so 
 ingeniously devised by the makers, for microscopists with 
 long purses ; but apparatus to answer the same purposes 
 may often be made by the ingenious worker, which, though 
 not possessing such a good appearance, serve just as well 
 as the more expensive articles. 
 
 Many microscopists, after a few years' devotion to their 
 favourite instrument, find themselves encumbered with a 
 host of paraphernalia of no use to themselves or to any one 
 else, the cost of which might have been saved by con- 
 sidering beforehand the capabilities of the required appa- 
 ratus. As to instruments, each individual taste has to be 
 considered, some prefer one pattern and some another ; 
 but, after all, these matters are easily arranged if the 
 principle of construction is good. 
 
 The main office of the microscope is that of enlargement ; 
 but this amplification of the image of an object must be 
 attained without distortion or the introduction of colours 
 not in the original, and it is because single lenses give 
 images blurred with spherical and chromatic aberration 
 that double and triple combinations are used in the con- 
 struction of all good microscopes. Single lenses are how- 
 ever very useful for general purposes: as a pocket lens, 
 it prevents the collection of much useless material during a 
 naturalist's rambles, and upon reaching home a further use 
 is found in its employment as an aid in dissecting or in 
 mounting the objects culled. The most useful magnifiers 
 are the ordinary watchmakers' or engravers' eye-glasses in 
 the usual horn mount, but their amplifying power should 
 not be too great or continued use may impair the eyesight. 
 
 A combination of several single lenses, such as is shown 
 in Fig. i, is much used as a pocket magnifier for the field 
 
BRO WNINGS PLA TVS CO PIC LENSES. 5 
 
 where a high power is not required ; they are cheap, but 
 the lower powers only are generally useful. The Stanhope 
 and Coddington lenses are also used by some collectors, 
 though there is little doubt that they are going out of date 
 on account of their not being so useful as newer forms of 
 the simple microscope. 
 
 The Stanhope magnifier is a double convex lens having 
 two unequal curvatures. In observing, the deepest curve 
 is placed towards the eye, the object 
 adhering to the least convex side being 
 just in focus. The Coddington lens is 
 generally a sphere of glass, round the 
 periphery of which a deep groove has 
 been cut and filled up again with black 
 cement. This lens focusses at a short 
 distance from the object, and is much 
 superior to the Stanhope form. Inferior p 
 
 Coddingtons are now made from re- 
 jected double convex lenses which do not act as well as 
 the form described. 
 
 Without doubt the best magnifiers for field use and 
 such work generally are the platyscopic lenses of Mr. 
 John Browning, which he makes of three degrees of 
 power, amplifying 15, 20, and 30 diameters respectively. 
 They are really achromatic triplets, are set in ebonite 
 cells, and mounted in tortoise-shell frames. These 
 lenses focus at about three times the distance from an 
 object as a Coddington of the same power, and so allow 
 of the easy examination of opaque objects. They are 
 shown engraved full size in Fig. 2. Steinheil has produced 
 similar lenses, which he terms " aplanatische loupen " ; they 
 are of similar construction to the above, and are made to 
 magnify 5j, 8, 12, 1 6, and 24 diameters. 
 
 One of these lenses, or, preferably, two of them, carried 
 
PRACTICAL MICROSCOPY. 
 
 in the pocket when field hunting, will prove of invaluable 
 assistance to the student. The most useful powers will be 
 found in those amplifying 1 5 and 30 diameters : the former 
 serves well for the examination of mosses, ferns, lichens, 
 algae, and such members of the animal world as can be 
 
 FIG. 2. 
 
 recognised by the aid of a 3-inch objective and the A 
 eye-piece, to which combined, it is about equal in power ; 
 whilst the smaller glass, giving greater amplification, 
 answers admirably for micro-fungi, minute algae and 
 lichens, and those forms of animal life for which a i-J-inch 
 objective is desirable. 
 
 If the reader refers to any work treating upon optics, he 
 will find that convex lenses yield images in two distinct 
 manners virtital images and real images. A double 
 convex lens, when used as an ordinary magnifying glass, 
 produces a virtual image which is erect and larger than 
 the object, as may be seen by reference to Fig. 3. 
 
 The greater the convexity given to the surfaces of the 
 lens, the more will it amplify, and it may also be said 
 
VIRTUAL AND REAL IMAGES. 
 
 that the nearer the object be placed to the principal focus 
 of the lens (F) for parallel rays, the larger will the virtual 
 image appear. To yield a virtual image, the object must 
 be placed between the lens and its principal focus. 
 
 FIG. 3. 
 
 A real image is formed from a double convex lens, only 
 when the object is outside, or in front of, the principal focus 
 for parallel rays ; this image is inverted, and may be studied 
 by receiving it upon a screen of ground glass. The action 
 of lenses in the production of real images should be care- 
 fully considered by the student, as upon it depends chiefly 
 
 FIG. 4. 
 
 the results of his manipulation, which may be perfect or 
 defective in proportion as he understands the theory of 
 this simple optical instrument. 
 
 An inspection of Fig. 4 will show the two consequences of 
 this action. If A B represents a lighted candle placed far 
 distant from the principal focus of the lens, a small, real 
 
8 PRACTICAL MICROSCOPY, 
 
 but inverted image of the candle will be thrown upon the 
 screen at a d, and the further A B is placed away from the 
 principal focus for parallel rays, the smaller will be a b, and 
 the nearer will it be formed to the opposite principal focus. 
 On the other hand, if a b represents the lighted candle 
 placed in front of the principal focus F but very near to it, 
 the real image which is formed, A B, is much amplified, in 
 proportion as a b is nearer to the principal focus, and the 
 distance at which A B is formed is likewise regulated by 
 the distance of the object from this point. The nearer a b 
 is to F, the further will A B be formed away from the lens, 
 and vice versd. 
 
 The student will now be able to see the principle upon 
 which the microscope is constructed, and, in closing this 
 chapter, we do so by giving a table of the magnifying 
 power of single convex lenses of varying focal lengths, for 
 parallel rays at a distance of 12 J inches from the micro- 
 meter to the screen, which has been constructed from a 
 paper upon the subject by Dr. Woodward in 'Silliman's 
 Journal' for June 1872. 
 
 Focal Distance Amplification 
 
 for in 
 
 Parallel Rays. Diameters. 
 
 i" .;. ...... 10-4 
 
 ...... 23-0 
 
 F ........ 48-0 
 
 F ...... .. 98-0 
 
 T y ........ 198-0 
 
CHAPTER II. 
 
 THE MICROSCOPE STAND. 
 
 As we are supposed to be treating nearly exclusively of 
 compound microscopes that is to say, of instruments in 
 which the amplification of an object is produced by means 
 of a combination of lenses called an " objective," the image 
 being further magnified by another set called an " ocular " 
 or " eye-piece " we will consider that our readers require 
 no demonstration as to the necessity of some mechanical 
 contrivance for holding these lenses in their correct 
 positions. 
 
 This is the office of the stand of a compound microscope, 
 and when we notice the progress which has been made in 
 the details of this instrument from the time the first was 
 made for sale in England by Mr. John Marshall, we shall 
 find that not to opticians only, properly so called, are we 
 indebted for improvements, but to mechanicians equally. 
 It was but of little use attempting to perfect the optical 
 arrangements while the mechanical contrivances were 
 imperfect, and when this was fully appreciated, real 
 improvements were made by mechanics and optics working 
 hand in hand. At the same time, we must not forget the 
 aid which has been rendered by amateurs and micro- 
 scopists with unlimited means at their disposal; it is 
 certain that many of the early and even the more recent 
 improvements would not have been executed, except at 
 the instance of one possessing a well-lined purse and with 
 great interest in the science. 
 
10 
 
 PRACTICAL MICROSCOPY. 
 
 As previously mentioned, the chief function of the 
 microscope stand is to receive the eye-piece and objectives ; 
 
 FIG. 5. 
 
 but it has to do much more than this, and upon its form 
 and general construction, together with the character of 
 
THE ROSS MODEL. 1 1 
 
 the workmanship, depends the excellence of the work it is 
 able to perform. 
 
 The two principal models, upon which nearly all stands 
 are made, have been named the " Ross model " and the 
 " Jackson model," both of which may be studied in the 
 productions of Messrs. Ross & Co. Fig. 5 shows the Ross 
 model, in which the body is attached by its base to a 
 transverse arm, which latter is borne on the summit of a 
 racked stem, to be seen in the figure. 
 
 This is a very efficient and convenient form when the 
 workmanship is good, and leaves nothing to be desired 
 if the stem and transverse arm are sufficiently solid. At 
 the same time, it is the worst model on which to make 
 cheap instruments, as those who have used them will only 
 be too ready to testify. A cheap stand made on the Ross 
 model practically requires no fine adjustment, there being 
 sufficient spring in the stem and arm to focus with, by slightly 
 pressing upon the latter at its junction with the body. 
 
 In the Jackson model, shown in Fig. 6, the body has the 
 rackwork attached to it, and is supported for a great part of 
 its length on a solid limb, as shown in the figure. It is, there- 
 fore, much less liable to vibration than in the Ross model. 
 
 In a paper read before the Royal Microscopical Society 
 in March 1870, Dr. Carpenter detailed his experience of 
 these two forms of instruments. He sums up as follows : 
 " My own very decided conviction is that the adoption of 
 the principles of the Jackson model would be decidedly 
 advantageous alike for first-class instruments, in which the 
 steadiness of the image when the highest powers are being 
 employed ought to be of primary consideration ; for those 
 second-class instruments which are intended, at a less cost, 
 to do as much of the work of the first class as they can be 
 made to perform, portability here being of essential im- 
 portance; and for those third-class instruments in which 
 
12 
 
 PRACTICAL MICROSCOPY. 
 
 everything has to be reduced to its simplest form, so as to 
 permit the greatest reduction in their cost." 
 
 FIG. 6. 
 
 This summary of Dr. Carpenter's is so complete in its 
 apology for separating microscope stands into three classes, 
 
THE POWELL AND LE ALAND STAND. 13 
 
 that we will not add a word more. The first-class stands 
 are usually made from harder metal than the cheaper 
 instruments, in which reduction of cost is an important 
 item : this enables the former to wear better, the screws 
 and racks allowing of a great deal of work before they 
 begin to exhibit " backlash." The productions of Messrs. 
 Ross & Co., Messrs. R. and J. Beck, and Messrs. Powell 
 and Lealand deserve to be placed in the highest rank, as 
 microscopes of the first water, and we cannot do better 
 than describe them. 
 
 The two different patterns made by Messrs. Ross, and 
 shown in Figs. 5 and 6, are furnished with an extremely 
 solid foot, which is cast in one piece. The "coarse adjust- 
 ment " may be easily understood from the illustration, and 
 the "fine adjustment" is obtained by the action of a milled 
 head upon a lever which moves the nose-piece, in either 
 case. Both instruments are furnished with a centering and 
 traversing substage, and also with a rotating movement 
 which is worked by a rack and pinion. The stage itself is 
 very complete, the object slide when laid upon it can be 
 instantly secured in position, and the whole stage with the 
 object in situ can be rotated round the optical axis as 
 a centre. The circular motion is graduated, and thus 
 answers many useful purposes. A rectangular motion in 
 two directions can be imparted to the stage by means of 
 two milled heads. 
 
 In the most recent forms of instrument the stage is 
 made very thin (so far as is consistent with steadiness), and 
 the central opening large, so as to admit light of great 
 obliquity, for which purpose the mirror is placed at the end 
 of a jointed arm, so that it may be considerably extended. 
 
 The large best microscope of Messrs. Powell and Lealand 
 is very heavy and massive ; Dr. Lionel Beale speaks of it 
 in high terms of praise. The focussing movement is upon 
 
FIG. 7. 
 
BECKYS INTERNATIONAL STAND. 15 
 
 the Ross model, but the pattern itself is quite unique, and 
 though of different construction to other forms, responds 
 satisfactorily to all the requirements of the microscopist. 
 
 The stage has one inch of motion in two directions, by 
 means of the milled heads, and is capable of rotation round 
 the optical centre by means of a wheel and pinion. This 
 is combined with a very thin stage for oblique illumination 
 of objects, either by means of the mirror or the achromatic 
 prism. There is also a graduated silver circle, which can 
 be used as a goniometer or for a variety of purposes. 
 
 The substage has rotary, vertical, and rectangular 
 motions, and both stages have for their foundation a solid 
 brass ring, which is firmly attached to the stem. This 
 stand is a specimen of excellent workmanship produced 
 regardless of cost, in order to give those who require and 
 can afford it perfection. 
 
 With the best stand of Messrs. Beck we encounter a 
 difficulty. It was our intention at the outset to describe 
 those instruments furnished with swinging substages, under 
 a special heading, but the best or " International " stand of 
 Messrs. Beck being furnished with these additions, we feel 
 constrained to mention it here. See Fig. 7. 
 
 All the instruments turned out from the factory of these 
 opticians are made upon the Jackson model (by whom 
 indeed it was first adopted) with the single exception of 
 their "popular" microscope, which is focussed on the 
 Ross principle. The " International " has a heavy brass 
 tripod for its base, upon which is placed a revolving gradu- 
 ated fitting, from which rise two pillars, together forming 
 the foot. Between these pillars is hung the limb which 
 carries the body at its upper end. In its centre the com- 
 pound stage is fixed, beneath which is a circular plate 
 carrying the swinging bar and substage. 
 
 The stage itself is attached to the limb on a pivot, and 
 
FIG. 8. 
 
STANDS OF MEDIUM PRICE. 17 
 
 can be set to any angle of inclination, the plate being 
 divided so that the angle may be recorded, and in this way 
 also, light of any degree of obliquity may be used without 
 interference from the thickness of the stage. Horizontal 
 movements by two milled heads are capable of being 
 imparted to the stage, which may also be revolved by 
 means of a milled head, or when this is pulled out, by 
 using the two ivory studs fixed to the top plate for that 
 purpose. 
 
 For a description of the substage, we must refer our 
 readers to a later portion of this chapter, wherein special 
 forms of instruments are described, and in concluding a 
 notice of these microscopes, urge every one who is wishful 
 to possess a first-class instrument to see the work of each 
 of these three firms before deciding. One cannot be too 
 careful in the selection of an instrument, and we have nearly 
 always found that if any one has rushed blindly into the 
 purchase of a microscope on the recommendation- of a 
 friend, sooner or later he has been dissatisfied with it, and 
 has finally purchased another of his own choice. 
 
 Other opticians produce as specialities good working 
 stands at a medium price. 
 
 Swift's " Challenge Binocular " is shown at Fig. 8, and 
 has been in especial favour during the past few years ; it is 
 a good working instrument, especially when combined with 
 his universal substage condenser. The general construction 
 of the stand will be seen on reference to the figure ; it is 
 not too tall or large, and is exceedingly well balanced. 
 
 Collins* " Harley Binocular," though formerly made upon 
 the Ross model, is now constructed upon the Jackson 
 model, and has this advantage, that commencing with 
 a simple stand, a very complete instrument, such as 
 shown by Fig. 9, can be built up from it. The stage is 
 made to rotate and also to move by means of milled heads 
 
 c 
 
FIG. 9. 
 
ROYAL MICROSCOPICAL SOCIETY'S SCREW. 19 
 
 in two rectangular directions, so that the remarks made 
 in Dr. Carpenter's 'Microscope' do not now apply 
 to it. 
 
 Crouch's "Premier Binocular" is also one of the first- 
 class instruments. An illustration of it is given in 
 Fig. 10. 
 
 Messrs. Pillischer, Browning, Murray and Heath, Baker, 
 Watson, and others make medium priced stands of con- 
 siderable excellence, but seeing that all the principles of 
 construction are exhibited in the foregoing, it would be 
 mere repetition to give illustrations of each. 
 
 After all, a microscope stand must satisfy certain con- 
 ditions, and if these be fulfilled it scarcely matters to the 
 owner who the maker has been. It must be made of 
 good hard brass, be furnished with a heavy foot, and well 
 balanced, so that it may be placed in any position without 
 overturning. All the rackwork and screws must move 
 easily, firmly but not stiffly, and without " loss of time " or 
 " backlash." Stops should be placed so that the body may 
 be set either horizontally or vertically as required, and 
 plane and concave mirrors should be always provided, 
 preferably on a jointed arm. The lower extremity of 
 the body should be furnished with the Society's screw, 
 and no microscope should be purchased which has not this 
 thread. 
 
 A mechanical stage is not absolutely necessary but is a 
 great convenience, despite all opinions to the contrary, and 
 some accessories cannot be used without it. A circular and 
 rectangular motion should be capable of being imparted to 
 the stage without the intervention of rackwork ; but a 
 duplicate motion by means of rack and pinion should be 
 supplied to the better instruments. Reasons for the rota- 
 tion of the stage will be found in the chapter treating on 
 the use of the polariscope. 
 
 C 2 
 
20 
 
 PRACTICAL MICROSCOPY. 
 
 The medium and best stands should be furnished with 
 an adjusting substage fitting, capable of being moved verti- 
 
 FlG. 10. 
 
BROWNINGS ROTATING MICROSCOPE. 
 
 21 
 
 cally by means of rack and pinion ; but the cheaper kinds 
 are usually provided with a removable tube, into which the 
 polariscope, condenser, and other accessories are made to 
 fit. These should be capable of taking accessories made 
 to the one and a half inch gauge, even if purchased from 
 different makers. 
 
 A cheap but well-made microscope of special pattern has 
 been devised by Mr. Browning, in which the entire body 
 and stage rotates upon the same axis, perfectly concen- 
 tric even with the highest 
 powers. It has a large 
 circular glass stage, re- 
 movable stage -fitting for 
 apparatus, and is a very 
 good form for laboratory 
 or general use. It is made 
 both with monocular and 
 binocular bodies, the for- 
 mer of which is shown in 
 Fig. II. 
 
 A very good form of 
 portable microscope is 
 made by Mr. Browning 
 and shown in Figs. 12 and 
 13. The stage is fitted 
 with rectangular and cir- 
 cular motions, has an ad- 
 justable substage with cen- 
 tering movements, and is 
 fitted with plane and concave mirrors on jointed arm. 
 When fitted up for use it is as steady as a stand of the 
 ordinary make, as the author can testify, and is shown in 
 this position in Fig. 12. By a novel arrangement the body 
 of the microscope turns on a joint and packs away with- 
 
 FlG. II. 
 
22 
 
 PRACTICAL MICROSCOPY. 
 
 out detaching any portion of the instrument, as shown in 
 Fig. 13. The stand also folds in a novel manner and 
 packs into a case, the outside dimensions of which are 
 6x6x9 inches. 
 
 FIG. 12. 
 
 It may now be as well to notice those forms of micro- 
 scope to which swinging substages have been adapted, or 
 
MR. GRUBB'S IMPROVEMENTS. 
 
 those forms whereby the same effects may be obtained by 
 other means. In 1854 Mr. Grubb, of Dublin, in a Pro- 
 visional Specification for Improvements in Microscopes, 
 stated, " My third improvement consists in the addition of 
 a graduated sectorial arc to the microscope concentric to 
 the plane of the object in situ, on which either the afore- 
 said prism or other suitable illuminator is made to slide, 
 thereby producing every kind of illumination required for 
 microscopic examination, and also the means of registering 
 
 FIG. 13. 
 
 or applying any definite angle of illumination at pleasure." 
 This seems to be the embryo of the modern swinging sub- 
 stage, which was not, however, developed in this country 
 until Zentmayer, in America, produced stands with these 
 modifications in the regular course of business. 
 
 As an instance of the pattern and the price at which 
 these stands are sold in the United States may be men- 
 tioned the Biological stand sold by Bulloch of Chicago. 
 The microscope stands I2j inches high and the stage 
 
24 PRACTICAL MICROSCOPY. 
 
 is 3J inches from the table. The body is 5 inches 
 long and the draw-tube also 5 inches in length, marked 
 with a ring to show the standard length. The diameter 
 of the body-tube is 1*4 inch. The stage has a revolving 
 concentric movement, the mirror and substage can be 
 made to swing over the tube, and there are spring stops 
 to indicate when they are in a line with the axis of the 
 instrument. The lower end of the main tube is fitted with 
 the Butterfield broad-gauge screw, forming an adapter 
 which carries the Society thread. The price of this instru- 
 ment in walnut case is, with one eye-piece $40, equal to 
 about SI. Ss. of our money, or with j-inch and |-inch 
 objectives I2/. It is shown by Fig. 14. 
 
 After the introduction of these swinging substages by 
 Zentmayer the manufacture of them was taken up in this 
 country by Messrs. Ross and Co., of New Bond Street, so 
 that those who desire to be furnished with the latest im- 
 provements or modifications of the instrument can easily 
 be supplied. The methods of construction are very similar 
 both in the American and English instruments, though the 
 superior workmanship of details in Fig. 15, over the 
 Biological stand of Bulloch, is only to be expected owing to 
 the difference in price. 
 
 This instrument is constructed on the Jackson model, 
 and is particularly free from tremor. The coarse adjust- 
 ment is effected by means of the ordinary rack and pinion, 
 the fine movement being worked by the action of a micro- 
 meter screw acting on a lever, by means of which the body 
 is not touched when using the fine adjustment, and as the 
 length is not changed, the relative distance of object-glass, 
 binocular prism, and eye-piece remains the same. 
 
 The substage bar which carries the mirror, condenser, 
 and other substage illuminating apparatus, swings from a 
 pivot placed behind the stage, the axis passing through the 
 
BULLOCKS BIOLOGICAL MICROSCOPE. 2$ 
 
 object when in situ, and remains in the focus of illumination 
 in every position of obliquity of the bar. The angle may 
 
 FIG. 14. 
 
 be read off from a graduated circle on a sector at the upper 
 end of the bar. 
 
26 PRACTICAL MICROSCOPY. 
 
 For oblique illumination a very thin stage has been 
 devised by Mr. Wenham ; it has only one top-plate, with 
 rectangular and concentric rotary movements worked by 
 two milled heads upon the same axis. This stage has two 
 set-screws by means of which it can be easily and effec- 
 tually centered. It is bevelled on the edge and graduated 
 to serve as a goniometer. By releasing a strong clamp-nut 
 this stage can be at once removed and any other sub- 
 stituted. 
 
 The swinging substage attached to the " International " 
 microscope stand of Messrs. R. and J. Beck may be seen 
 in Fig. 7. It is mounted perfectly true with the body, and 
 is moved up and down in its fitting by means of milled 
 heads. In this fitting all the varied appliances for modi- 
 fying the character and direction of the light are fitted. 
 The bar into which the substage fits is itself attached to an 
 arc working in a circular fitting, and is capable of rotation 
 by means of a milled head, so that it may be carried round 
 and above the stage if necessary. The amount of angular 
 movement may be recorded from the graduated circle. 
 The lower triangular bar carries the mirror when the illumi- 
 nation is required to be concentric with the optical axis of 
 the instrument ; when desired it can be made to slide on 
 the substage bar, and then can be moved above or below 
 the stage in the same manner as the substage, Messrs. 
 Swift and Son have produced what they term a " Radial 
 Traversing Substage Condenser," in order to produce the 
 same results in illumination as can be obtained with swing- 
 ing substages. Mention only is made here, as its construc- 
 tion and use will be fully explained when treating of 
 accessories. 
 
 Messrs. Watson and Sons, of Holborn, have recently 
 patented the arrangement, an illustration of which is shown 
 in Fig. 1 6. In this the mirror is accurately centered, while 
 
THE ROSS-ZENTMA YER STAND. 
 
 the body of the instrument, together with the stage, is made 
 to incline in order to arrive at the same results as attained 
 with the foregoing accessories. 
 
 It will be seen that the new stand enables the observer to 
 
 FIG. 15. 
 
28 PRACTICAL MICROSCOPY. 
 
 examine an object as he would if it were held in the hand, 
 and viewed by the naked eye that is, to turn it about in 
 every possible way towards a ray of light proceeding in a 
 fixed direction and so, without once losing sight either 
 of the light or the object, to observe its appearance when 
 illuminated by light of every degree of obliquity. 
 
 This is the fundamental idea underlying its construction, 
 and in this consists the great difference between it and the 
 old forms of stand (although it has all the uses of the latter), 
 where the object remaining fixed, the only way in which its 
 illumination can be varied is by moving the illuminating 
 ray which, in the amount of the results it affords, and the 
 amount of time it consumes, is stated by the inventors to 
 be in every way inferior to the new one. 
 
 An inspection of the engraving (Fig. 16) will show how 
 this idea is worked out. On the top of a strong pillar, to 
 which it is attached by a massive cradle-joint allowing of 
 inclination in a vertical plane, is fixed the arm carrying the 
 body, which latter is provided with rack adjustment, and a 
 new and improved fine adjustment, rendering unnecessary 
 the usual often unsatisfactory loose nose-piece. The stage 
 is so fixed with regard to the arm that the object when 
 lying upon it is in a line with the centre of the cradle-joint, 
 so that upon inclining the body the object moves with it, 
 and is presented at every possible vertical angle to a ray 
 proceeding to it from a given direction. The stage is of a 
 new and improved construction, being exceedingly thin 
 in fact the thinnest mechanical stage yet devised and is 
 capable of giving a complete rotation of the object. 
 
 Beneath the stage swings the substage arm, concentric 
 with the object, and carrying the usual screw centering and 
 rack adjusting substage. 
 
 Behind the substage arm is a strong bar, provided with a 
 dovetailed groove, into which the mirror bar slides. This 
 
WA TSOWS NEW MICROSCOPE. 2Q 
 
 is so pivoted to the substage arm as to allow the latter to 
 be swung aside and the mirror used alone when requisite, 
 without the trouble of taking the substage away altogether. 
 This is a great advantage, as it permits the substage, and 
 any apparatus it may be carrying, to be swung into or out 
 of position in a moment with the mirror in the position here 
 indicated. The stand has all the uses of the old forms of 
 microscope, and can be employed in exactly the same way, 
 but even then its peculiar motions round the object as 
 a centre give it very great advantages in every class of 
 investigation. But it is when the mirror occupies the 
 position now to be described that the peculiar properties 
 of the new stand are brought fully into play. 
 
 The upright pillar, carrying the body and stage, is 
 attached at its foot to a massive circular plate, carrying a 
 graduated circle which rotates round a point exactly 
 beneath the centre of the stage ; and moving independently 
 and concentrically with this is another smaller circle, 
 having a dovetailed groove ploughed across it, into which 
 the mirror bar can be slid when withdrawn from the sub- 
 stage arm. A spring catch attached to the dovetailed 
 circle falls into a notch in the mirror bar when the centre 
 of the mirror is exactly beneath the centre of the stage. 
 This is the most useful position for the mirror, as a ray fall- 
 ing from a source of light upon it may be reflected upwards 
 perpendicularly upon the object, when the body of the 
 microscope is vertical, then without interfering again either 
 with the mirror or lamp, or interposing any accessory 
 apparatus whatever, but simply by inclining the body, the 
 light falls upon the object with a gradually increasing 
 obliquity until, when the instrument is nearly horizontal, a 
 perfect dark-ground illumination can be obtained even 
 with the highest powers, while the gradual way in which 
 the light becomes more and more oblique immediately 
 
FIG. 16. 
 
MR. WENHAM^S BINOCULAR. 31 
 
 under the eye, and the capability of arresting the incli- 
 nation at that point where the most suitable illumination 
 for the object under examination is obtained, give to the 
 observer powers he has seldom before had at his command 
 in any form of microscope yet produced. 
 
 The horizontal rotation mentioned above allows the object 
 to be directed to the light at every angle in azimuth to 
 borrow a term from the astronomer as the cradle-joint on 
 the top of the pillar gives every angle in altitude ; the 
 object occupying the centre of both motions, by a combina- 
 tion of the two it can of course be placed in every possible 
 position. These angles are read, the latter by a graduated 
 circle in the outer side of the cradle-joint, giving the incli- 
 nation of the body to the vertical, the former by means of 
 the graduated circle at the foot; readings of these circles 
 being taken with the mirror placed as above described at 
 any time by so fixing the instrument that these circles 
 read the same. Any desired effect will be exactly repro- 
 duced, wherever the lamp may be placed a point of the 
 greatest importance to workers with high powers. - 
 
 There is a third divided circle on the substage axis, 
 giving the inclination of the substage to the axis of the 
 body. A strong clamp on the outer side of the cradle-joint 
 holds the body firmly at any inclination, and a graduation 
 on the slide of the coarse adjustment enables the working 
 distance of the objectives to be measured and compared. 
 
 Time alone can show whether these present apparent 
 advantages are lasting, or whether the instrument will wear 
 as well as those of the old form of construction. 
 
 The foregoing illustrations of microscope stands are seen 
 to be both monocular and binocular that is to say, used 
 with one or two eye-pieces. A binocular should always be 
 purchased when the student's means are sufficient, as most 
 objects can be studied with much more ease and comfort 
 
PRACTICAL MICROSCOPY. 
 
 than with a monocular microscope. Binocular instruments 
 are made in such a manner that the rays proceeding from 
 an object lying upon the stage are split into two parts, 
 each portion passing separately through a tube to the 
 eye-pieces, as shown in Fig. 17. 
 
 The form of prism used for dividing the rays (we may say 
 universally) is that devised by Mr. Wenham many years 
 ago. It is mounted in a small brass box, sliding into the 
 lower end of the microscope body immediately over the 
 
 objective, as shown in Fig. 17. 
 A section of this prism is shown 
 in Fig. 1 8, the dotted line indi- 
 cating the direction of one por- 
 tion of the divided ray. 
 
 It should not be forgotten 
 that a binocular of this form is 
 
 FIG. 17. 
 
 FIG. 18. 
 
 not well suited for use with objectives of a higher numerical 
 aperture than o 34 or 40 air angle ; a certain amount of dis- 
 tortion occurs with higher apertures, which may be readily 
 perceived on the examination of spherical pollen-grains and 
 such like objects. Dr. Carpenter has pointed out this ex- 
 aggerated relief years ago, yet there are some folks now 
 
THE STEPHENSON BINOCULAR. 33 
 
 who delight in showing this imperfection as one of the 
 beauties of the binocular microscope. 
 
 It will thus be seen that objectives of higher amplifica- 
 tion than the half-inch cannot be satisfactorily used with 
 the binocular, and even the half-inch requires making of 
 specially small aperture to adapt it to this use. The 
 prism is always made removable, so that at any time the 
 microscope can be used as a monocular by simply with- 
 drawing it. 
 
 In order to enable observers to use binocular vision with 
 high powers, Messrs. Powell and Lealand have devised a 
 system of prisms which may be used with objectives as 
 high as the -$ The images produced are not stereoscopic, 
 but exactly similar. Mr. Wenham has also devised prisms 
 for using high powers binocularly, which appear to act in a 
 very successful manner. 
 
 Tolles, of Canastota, U.S., makes a binocular eye-piece for 
 the ordinary single body, which gives a large and well-illu- 
 minated field with low and medium powers. Professor 
 H. L. Smith remarks that he has used the ^ and ^ 
 objectives with it. 
 
 Another binocular microscope was devised some years 
 ago by Mr. J. W. Stephenson, which has since been success- 
 fully made by Mr. Browning. Within the last few years 
 the cost of this instrument has been considerably reduced, 
 Messrs. Swift and Son and Mr. Baker having each con- 
 structed a Stephenson binocular for dissecting purposes at 
 the moderate price of //. 
 
 The Stephenson binocular, as made by Mr. Browning, is 
 shown at Fig. 19, in which the change from binocular to 
 monocular or vice versd can be effected without unscrewing 
 any part or interfering with the object under examina- 
 tion. 
 
 In this form of binocular the rays are divided by two 
 
 D 
 
FIG. 19. 
 
THE "STEPHMNSON* PRISMS. 
 
 35 
 
 prisms A A, Fig. 20, which, passing upwards, are reflected 
 towards the eye-pieces by the triangular prism B, Fig. 21. 
 The instrument is erecting that is to say, objects are pre- 
 sented to the eye in a normal manner, and not inverted 
 as in the ordinary form of instrument, which adapts it 
 specially for use in dissecting. The bodies of the micro- 
 scope are made to rotate, carrying the prisms with them, 
 so that two observers may work with the instrument, 
 
 FIG. 20. 
 
 FIG. 21. 
 
 observe the same object, and compare notes without alter- 
 ing the conditions under which the object is being 
 examined. 
 
 Amongst the foregoing medium and best stands, the 
 reader must be fastidious indeed if he is not able to find 
 one to suit his choice. Price might be a deterrent, and 
 therefore some illustrations are given of several microscopes 
 which, though cheap, are good working instruments. 
 
 Fig. 22 is the Economic monocular microscope of Messrs. 
 R. and J. Beck, which with coarse and fine adjust- 
 ment, I -inch and J-inch objectives, two eye-pieces, con- 
 cave mirror, side condensing lens, diaphragm, forceps, 
 pliers, and glass slip with ledge, in mahogany case, costs 
 61. I2s. 6d. A small cheap stand such as this is nearly 
 always required by the practical microscopist, even if he 
 possesses a first-rate instrument; for travelling, Society 
 
 D 2 
 
FIG. 22. 
 
THIRD CLASS MICROSCOPES. 
 
 37 
 
 demonstrations, dissecting, and many other purposes a 
 small microscope is exceedingly useful. 
 
 Another cheap instrument, which is furnished by several 
 makers, is shown in Fig. 23 ; it has a sliding body for 
 coarse adjustment, a fine 
 adjustment, draw - tube, 
 wheel of diaphragms, tube 
 fitting for substage appa- 
 ratus, plane and concave 
 mirrors, one eye-piece, i- 
 inch and J-inch objectives, 
 and stand condenser, in 
 mahogany case, for which 
 is charged the moderate 
 price of 5/. 12s. 6d., to 
 which can be added after- 
 wards a polariscope for 
 25^., a camera lucida 6s., 
 and a stage micrometer 
 for 5^-. 6d. 
 
 Equipped with one of 
 these instruments, which 
 are remarkably steady, 
 being hung on the Jack- 
 son model, the student 
 is ready for an immense amount of work, and it is 
 certainly much better to invest in an instrument such as 
 this than to waste money on a cheaper instrument which 
 has not the Society's screw. In the purchase of a low- 
 price stand, we would give the student the following 
 advice : Never purchase a cheap instrument made upon 
 the Ross model ; never purchase one which will not take 
 objectives with the Society's thread without an adapter ; 
 never purchase an instrument without a fine adjustment, 
 
 FIG. 23. 
 
PRACTICAL MICROSCOPY. 
 
 without it be for petrological studies merely; and above all 
 do not purchase the extremely trashy foreign separating 
 
 objectives. If you want 
 foreign glasses, there 
 are good ones to be 
 bought buy them. 
 
 After all, there are a 
 few objections to the 
 form of instrument 
 shown at Fig. 23. The 
 body tube is narrow and 
 the field lens of the eye- 
 piece small in propor- 
 tion, so that the field is 
 limited in size ; then, 
 again, the absence of 
 a coarse adjustment 
 may for some purposes 
 be found inconvenient, 
 while the fitting below 
 the stage should be 
 made removable. On 
 the other hand, the short 
 tube gives a larger field 
 when used for photo- 
 micrography, and is also more convenient as a dissecting 
 microscope, lengthening as it does the anterior conjugate 
 focus and giving more room for the needles. 
 
 Recognising these and several other advantages, the 
 author had one specially constructed, as shown in Fig. 24. 
 The draw tube is wide enough to take the full-sized eye- 
 pieces, and when it is fully extended the whole forms a 
 body of the ordinary length. The stage, together with the 
 body, may be rotated round the optical axis in the same 
 
 Fro. 24. 
 
A WORKING MICROSCOPE. 39 
 
 manner as has been already shown in Fig. n. There are 
 coarse and fine adjustments, a diaphragm in the thickness 
 of the stage, plane and concave mirrors, the whole costing 
 the author the moderate sum of three guineas and a half. 
 
 With this form one is not bound to bad or medium eye- 
 pieces and objectives ; they can be bought separately and 
 selected. We should like to see some enterprising manu- 
 facturer making the instrument as shown in Fig. 24, and 
 selling it for six guineas with an A eye-piece and a good 
 inch objective, or without eye-piece and objective for 3/. los. 
 The details of this instrument are as follow: When 
 standing vertically and closed down, the top of the eye- 
 piece is ii inches from the table, the collar in which the 
 body slides being 3 inches in length, and lined with velvet. 
 The body is 5 inches in length, and the draw-tube 4J inches, 
 with an outside diameter of 1*3 inches ; the stage is 
 3 7 inches from the table, and has a diameter of 3 inches ; 
 the mirrors are 2*2 inches in diameter, and the fine ad- 
 justment raises or depresses the entire body T -J-g- of 
 an inch for each complete revolution. The stage is less 
 than of an inch in thickness. The author has found 
 this a very convenient instrument for photomicrography 
 and for general microscopical work. The substage fitting 
 will take all accessories made to the usual I J-inch gauge. 
 
 It is greatly to be deplored that there exists no universal 
 gauge for eye-pieces and substage fittings, is it too much 
 to ask the Council of the Royal Microscopical Society to 
 take the matter in hand ? 
 
CHAPTER III. 
 
 EYE-PIECES AND OBJECTIVES. 
 
 Eye-pieces or Oculars. When the student purchases a 
 microscope stand, he will generally find it supplied with 
 the lowest power Huyghenian or negative eye-piece, usually 
 designated by the letter A. At the same time, it may be 
 stated that others, possessing greater degrees of amplifica- 
 tion are often substituted or added at the wish of the 
 purchaser ; and it should be remembered, in the selection 
 of a microscope stand, that the eye-pieces of one maker 
 will not always fit the tubes made by another. It is a 
 thousand pities opticians have not yet learned that their 
 time may be more profitably occupied than by making 
 adapters for each other's instruments. 
 
 The Huyghenian eye-pieces or " oculars " of low power 
 are generally styled "shallow," to distinguish them from 
 those which give greater amplification, which are called 
 " deep " the terms deep and shallow being applied to the 
 degree of curvature possessed by the lenses employed in 
 their construction, and not to the distance between them, 
 as some writers have stated. 
 
 A full-size section of the Huyghenian A eye-piece is 
 shown in Fig. 25, so that the student may understand the 
 details of its construction. 
 
 It consists of two plano-convex lenses, placed at a dis- 
 tance from each other equal to half the sum of their focal 
 lengths, the best proportion of relative radii being i to 3. 
 
THE HUYGHENIAN EYE-PIECE. 
 
 The lower lens is called the field-glass, and the upper 
 one the eye-glass, while a circular stop or diaphragm is 
 placed nearly midway between the two. 
 
 The practical optician Gundlach has stated that the 
 correction afforded by the Huyghenian eye-piece is not 
 a complete one ; for at the point 
 where the spherical aberration 
 is entirely corrected, the chro- 
 matic has not completely disap- 
 peared. This even at the most 
 favourable interval between the 
 two lenses. 
 
 This eye-piece was first em- 
 ployed by Huyghens for his 
 telescopes, in order to diminish 
 spherical aberration and to in- 
 crease the size of the field. An 
 elaborate dissertation upon it has 
 been published by Mr. Varley in 
 the ' Transactions of the Society 
 of Arts,' vol. li., to which the 
 student is referred. It is often 
 called the negative eye-piece, on account of its correcting 
 the positive aberrations of the objective. 
 
 In Fig. 26 is shown a section of a deep eye-piece the 
 Huyghenian C in which it will be seen that the lenses 
 possess deeper curvature than in the A, while the diaphragm 
 is more contracted, and the aperture in the cap covering 
 the eye-glass is very small indeed ; the C eye-piece gives 
 about double the amplification of the A. 
 
 There is another kind of ocular in occasional use, called 
 Ramsden's positive eye-piece ; it is formed of two plano- 
 convex lenses, but the curvature of the field-glass is turned 
 towards the eye instead of towards the object, as in the 
 
 FIG. 25. 
 
PRACTICAL MICROSCOPY. 
 
 Huyghenian. In this eye-piece the focus is obtained in 
 front of the field-glass, while in the Huyghenian ocular the 
 image is formed at the diaphragm, about midway between 
 the field-lens and eye-glass. 
 
 The Ramsden eye-piece was much in use at one time for 
 purposes of micrometry, as it gave an excellent view of the 
 micrometer, free from distortion even to the edges of the 
 field, though the image was slightly coloured. It is still 
 used by Messrs. Ross and Co. for their eye-piece micro- 
 meters. 
 
 FIG. 26. 
 
 FIG. 27. 
 
 Kellner's orthoscopic eye-piece is much employed where 
 a large and flat field is required for use with low powers. 
 A section is shown in Fig. 27, from which the student may 
 gather that the field-glass is doubly convex, and the eye- 
 glass a slightly under-corrected achromatic combination, 
 while the diaphragm is dispensed with altogether. 
 
 In the ordinary or Huyghenian ocular, English opticians 
 designate their power by means of letters, A, B, C, D, E, 
 and F, while some few call their productions by the numbers 
 i, 2, 3, 4, and 5 ; they seem fairly agreed as to what should 
 be the relative degrees of amplification of the A and B 
 eye-pieces, and some with the A, B, and C ; but with 
 higher powers there seems no uniformity, as the following 
 
RELATIVE POWER OF OCULARS. 
 
 43 
 
 table will show. The numbers have been calculated from 
 the catalogues of the different makers : 
 
 Objectives. 
 
 A 
 
 B 
 
 c 
 
 D 
 
 E 
 
 F 
 
 Ross 
 Powell an 
 Beck 
 Swift 
 Browning 
 Watson 
 Crouch 
 Collins 
 Baker 
 Pillischer 
 Parkes 
 Zeiss 
 Hartnack 
 
 dLe 
 
 alanc 
 
 1 
 
 
 o 
 
 o 1 
 
 'O 
 
 o 
 o 
 o 
 o 1 
 o 
 o 
 o 1 
 o 
 o 1 
 o 1 
 
 
 6 
 
 '5 2 
 
 4 
 3 
 4 
 
 o 2 
 6 
 6 
 6 2 
 
 I 
 
 2-0* 
 2'6 
 2'0 
 2*0 
 2'0 
 
 3'3 3 
 
 2'5 
 
 3 ' 3 
 
 3 . 3 
 2'2 
 
 i-8 3 
 i-5 3 
 
 4*o 
 4-0* 
 
 I'l 
 3'7 
 
 2'5 
 
 4-0 
 
 ft 
 
 2'6 4 
 2 . 3 4 
 
 5' 
 6'o 5 
 
 5'2 
 
 4'3 
 3'4 
 
 3' Si 
 3 . s 
 
 8-0 
 
 5'6 
 4'3 
 
 3'5 6 
 
 
 
 
 
 Our American brethren treat their oculars in a more 
 rational manner, they style them as "2-inch," " i-inch," 
 or otherwise, as the case may be, according to the degree 
 of amplification they yield when compared with single 
 lenses ; thus a " 2-inch ocular " would amplify the same as 
 a single lens of 2-inch focus, and so on in like proportion. 
 
 Now reference to Chapter I. will show us that a single 
 lens of 2-inch focus (equal to the English A eye-piece) 
 magnifies about five diameters at a distance of I2j inches 
 from the micrometer to the screen, and the i-inch, 10 
 diameters (equal to the C eye-piece), so that it is well 
 the student should as early as possible grasp the fact 
 that the amplification of an object is arrived at by two 
 stages, the objective producing an enlarged image of the 
 object, which the ocular magnifies still further. Roughly it 
 may be stated that if the inch objective be used with 
 the i-inch ocular an amplification of 100 diameters 
 is arrived at, the objective magnifying the object 10 
 diameters, the image of which is further magnified 10 
 diameters by the ocular ; and further, if the same objective 
 
44 PRACTICAL MICROSCOPY. 
 
 be used with the 2-inch ocular (the A eye-piece), the 
 former will produce an enlarged image of 10 diameters, 
 which the ocular will again magnify five times, producing a 
 total amplification of fifty. 
 
 This is not mathematically exact without every disturb- 
 ing element be taken into consideration, but is quite near 
 enough to illustrate the case in practice. Fifty diameters 
 is the recognised amplification for the i-inch objective 
 combined with the A ocular at a distance of 10 inches, and 
 as the enlargement of the object takes place in two distinct 
 stages, it will be seen that the optician is able to vary the 
 powers of both ocular and objective and still obtain the 
 standard result. An inch (so-called) objective magnifying 
 8 3 diameters when used with an A eye-piece magnifying 
 the image six diameters, will give a normal result, as will 
 an objective of the same designation magnifying 12 '5 
 diameters with an A ocular magnifying four. 
 
 Similar cases to both of these have recently fallen under 
 the notice of the author, and it is on account of like depar- 
 tures, that abnormal amplifications are obtained when the ob- 
 jectives of one maker are used with the oculars of another. 
 
 It often happens with new oculars that particles of brass 
 get detached, and fall upon the inner surface of the lenses, 
 which must be removed by unscrewing, and then carefully 
 wiping with a very soft wash-leather. Dust specks and 
 bubbles may be easily detected by deflecting a dull light 
 through the body of the instrument, when, by observation 
 during the rotation of the eye-piece, they show very plainly. 
 A good eye-piece should be perfectly transparent, and free 
 from striae and markings and spots of any kind. The 
 marginal circle of the field of vision should be sharp, clear, 
 and intensely black. If these conditions are not fulfilled, 
 the eye-piece cannot be considered as perfect, or fit for 
 general use. 
 
TULLE Y'S A CHROMA TICS. 45 
 
 Before proceeding to treat of objectives, the student may 
 be advised to commence with the 2-inch ocular (an A). 
 If he wishes for more than one power, the i-inch ocular 
 (C) is recommended, it being double the power of the A. 
 An orthoscopic C would perhaps be useful. 
 
 Object-glasses or Objectives. The history of the achro- 
 matic objective is a curious one interesting certainly, but 
 it should teach us the serious lesson not to be dogmatic in 
 our assertions. Biot and Wollaston, the latter especially, 
 were wedded to doublets, and they both predicted, on the 
 faith of certain experiments which were then unsuccessful, 
 that the compound microscope would never excel the 
 simple. How far this prediction has been verified most of 
 our readers will know; but it is certain that Wollaston 
 never thought that within fifty years of his prediction the 
 doublet would be a thing of the past, rarely heard of and 
 never seen. 
 
 Light seems to have dawned upon objective construction 
 through the elder Dollond, who employed two different 
 kinds of glass in the construction of his telescopes. 
 Recognising this principle, several foreign opticians made 
 partly corrected glasses as early as 1824, and at the same 
 time Tulley of London produced the first achromatic objec- 
 tive made in England : it was composed of three lenses 
 and possessed an air angle of 18, which he soon after 
 increased to 38 by placing another corrected combination 
 in front of it. 
 
 In the year 1829, Mr. Joseph Jackson Lister, in his cele- 
 brated paper published in the < Philosophical Transactions 
 of the Royal Society,' pointed out how many of the diffi- 
 culties could be overcome, and exhibited an objective 
 of 50 air angle which gave a large field and a correct 
 image. This advance was so great that it astonished 
 Dr. Goring, who wrote, in his 'Exordium to Microscopic 
 
46 PRACTICAL MICROSCOPY. 
 
 Illustrations,' that " microscopes are now placed completely 
 on a level with telescopes and, like them, must remain 
 stationary in their construction." 
 
 Improvements, however, continued to be effected ; Mr. 
 Thomas Ross, upon increasing the air angle, discovered 
 that different thicknesses of covering glass disturbed the 
 corrections for spherical and chromatic aberrations no 
 matter how carefully made, and in 1837 he presented a 
 paper to the Society of Arts upon the subject. In this 
 paper he stated having made an improved combination, the 
 focal length being one-eighth of an inch, with an air angle 
 of 60. After this he announced obtaining an air angle 
 of 135, and falling into a similar error of dogmatism as 
 Goring, Wollaston, and Biot, stated that "135 is the largest 
 angular pencil that can be passed through a microscope 
 object-glass." 
 
 In 1851, Chas. A. Spencer, of Canastota, N.Y., pro- 
 duced objectives of 146 air angle, and in 1857 he con- 
 structed a one-twelfth with an angle of 178. Since this, 
 Mr. Tolles, of Boston, has made lenses claiming to be 
 infinitely near 180, and this angle in air has been 
 approached by several of the best English makers. 
 
 But these are not the whole of the improvements which 
 have been effected ; air lenses or dry objectives have been 
 supplemented by water-immersion powers, and finally we 
 have the homogeneous-immersion system, in which the trans- 
 mitted ray pursues a rectilinear course from the under side 
 of the object slide until it leaves the posterior surface of the 
 front lens. These immersion lenses will be fully described 
 later on ; all we wish to state here in reference to them may 
 be said in the words of Prof. Abbe : " A wide angle immer- 
 sion glass may therefore utilise rays from an object in a 
 denser medium which are entirely lost for the image which 
 in fact do not exist when the same object is in air, or is 
 
CONSTRUCTION OF OBJECTIVES. 47 
 
 observed through a film of air ; " and again, " Consequently 
 we have a loss of aperture when an air angle of 180 is 
 substituted for a balsam-angle of ioo," for " an immersion 
 objective of balsam angle exceeding twice the critical angle 
 (41) has a greater aperture than any dry lens can ever 
 have." It was upon this subject that Mr. Wenham fell into 
 error and so may be classed with Ross, Goring, Wollaston, 
 and Biot. He denied that Tolles had produced, or could 
 ever produce an objective of greater balsam angle than was 
 equivalent to infinitely near 180 measured in air ; and those 
 who remember the correspondence on this subject which 
 appeared in the pages of the ' Monthly Microscopical 
 Journal/ will now smile when they see the announcements 
 in the 'Journal of the Royal Microscopical Society ' of the 
 productions of Messrs. Powell and Lealand of 1 50 balsam 
 angle. That memorable correspondence should teach us 
 to remember how easy it is to fall into error, and also that 
 it is quite easy to persuade ourselves we are well acquainted 
 with our subject, while at the same time we may totally 
 misunderstand it. 
 
 Objectives which, by-the-by, are sometimes called 
 " powers " being made from glass of varying density and 
 also of varying refractive indices, it follows that they must 
 differ also in construction in some degree. The various 
 lenses of which each combination is constructed are ground 
 to a series of curves, suitable to the glass employed, and 
 the combinations are placed at different distances apart, so 
 that we can only give a rough outline of their general 
 construction. 
 
 As a rule, objective mounts are turned out much too 
 long. There is no apparent reason why the brasswork 
 (of some opticians especially) should not be consider- 
 ably reduced. When the posterior lens is too far away 
 from the Wenham prism, in a binocular instrument, it is 
 
48 PRACTICAL MICROSCOPY. 
 
 extremely difficult to procure an equal illumination of the 
 whole field in fact, the general performance of the instru- 
 ment is seriously interfered with, and therefore, for use 
 with the binocular, short mounts should be preferred and 
 the longer ones rejected. 
 
 Mr. Swift has recently issued a series of objectives in 
 short mounts, especially for use with the Wenham binocular, 
 each of which allows of perfect illumination, without the 
 aid of an achromatic condenser. They range from i inch 
 upwards. 
 
 Objectives are generally spoken of in terms of the ampli- 
 fication which they yield, the standard of comparison being 
 the magnification given by a single lens of the nominal focus. 
 The student must not, therefore, imagine that an objective 
 stated to be i-inch, -inch, or so on, will focus at these 
 distances from the object. Opticians have never used the 
 term in that sense, though a few writers in public journals 
 seem to have understood the nomenclature in that light. 
 
 The degree of amplification, taken with the aperture, is 
 the surest guide to the focal distance ; for as the aperture 
 increases, the less will the working distance be, a point to 
 be considered in the selection of an objective for students' 
 use. 
 
 The lower powers are often made to separate. An 
 objective giving the amplification of a 2-inch when com- 
 plete, is converted into a 4-inch by removing the anterior 
 combination. Separating 2-inch and i-inch, i-inch and 
 J-inch, J-inch and i-inch, are also made, with others ; but the 
 student is advised not to invest much in these separating 
 powers. 
 
 The best low-power objectives for general work will be 
 found to possess the following air angles : 9 for the 
 4-inch, 15 for the 2-inch, while the i-inch seems to per- 
 form most satisfactorily at 30. 
 
THE SELECTION OF OBJECTIVES. 49 
 
 No objective with an air angle of more than 40 should 
 be used with the Wenham binocular. Dr. Carpenter 
 pointed out long ago the exaggerated effect of projection 
 produced when pollen-grains of the Malvacece and other 
 similar objects are examined binocularly with high-angle 
 objectives ; perfectly spherical objects, instead of resembling 
 a hemisphere, appearing like the small end of an egg. 
 
 Powers yielding amplifications ranging between 50 and 
 200 diameters may be called medium, and are represented 
 in our list by the J-inch and J-inch objectives. The former 
 is a very handy glass, though it does not seem to be an 
 easy one to construct, judging from many the author has 
 seen. Makers of cheap but really good i-inch and J-inch 
 powers seem to fail sometimes in producing cheap and 
 perfect J-inch objectives. 
 
 A good working J-inch may have an aperture of 60, 
 though it is made of 35 by Mr. Browning, and 40 by 
 Messrs. Powell and Lealand and Mr. Collins, for special 
 use with the binocular. 
 
 The medium and higher powers should be chosen with 
 conical fronts, as shown in Fig. 30, for with them it is 
 more easy to illuminate opaque objects satisfactorily. The 
 illustration is that of Mr. Swift's short mounted -inch 
 objective, with collar adjustment. 
 
 Zentmayer, Wray, and Zeiss have produced low power 
 objectives in which the two combinations composing them 
 are separated or brought nearer to each other by means 
 of a screw collar, the lens being nominally a 4-inch, a 2-inch, 
 or any intermediate power at will. This glass defines well, 
 and, moreover, possesses a flat field ; but, according to 
 measurement, the amplification it yields more nearly 
 approaches a 5-inch and 3-inch than an English 4-inch 
 and 2-inch. 
 
 For several years cheap foreign lenses -were in great 
 
 E 
 
50 PRACTICAL MICROSCOPY. 
 
 request, and much work has been done with them. This 
 has induced several English makers to offer a series of low- 
 angle objectives at a cheap rate, in addition to the really 
 good glasses which the same opticians turn out. Browning, 
 Wray, Watson, Swift, Dancer, Collins, and Parkes make 
 very excellent and cheap lenses for histological work. 
 
 It sometimes happens that very good powers may be 
 met with second-hand, or from the workshops of neglected 
 makers ; but the selection of a good glass from several of 
 average quality, though it can be done by an optician, or a 
 microscopist who has mastered the elements of science, is 
 not a very easy task, and one which certainly cannot be 
 performed by a novice on his first purchase of an instru- 
 ment. 
 
 Be very careful in purchasing objectives. Don't buy 
 trash, or any objective simply because it is cheap. Wait 
 until you can meet with a really good glass at the price 
 you are disposed to give, or be satisfied with the powers 
 you already possess. 
 
 For botanical and general work, especially if the student's 
 means are limited, the inch and J-inch objectives will 
 be found sufficient ; the 2-inch, and afterwards the J-inch, 
 may be added, if required ; following, if necessary, with 
 the ^-inch and ^-inch. A 4-inch power is used by some 
 for the examination of wood sections, whole insects, etc. 
 A cabinet will generally contain the following objectives by 
 the time the owner considers it furnished : 4, 2, i, J, , 
 ! -TO which yield degrees of amplification varying from 
 12 to 800 diameters with the A eye-piece, and 24 to 1600 
 with the C. 
 
 The low powers are constructed in several ways, ac- 
 cording to the aperture desired. Those of greater ampli- 
 fication than the i-inch are made either as triplets or of 
 two pairs of lenses placed at certain distances apart, as all 
 
THE ONE-INCH OBJECTIVE. 
 
 IS 
 
 the corrections required are easily made on this system. 
 The triplet, used only for low angles, is the least to be 
 commended, and should not be used with deep eye-pieces. 
 The i -inch objective may be a triplet, 
 as shown in Fig. 28, or a double combi- 
 nation, as in Fig. 29. 
 
 In the latter the front is a plano-con- 
 vex of crown, with a meniscus of flint, 
 being separated by a considerable inter- 
 val from the posterior combination, which 
 is composed of two double convex crown 
 lenses, holding between them a double 
 concave of flint. 
 
 It will be seen from Figs. 28 and 29 
 
 FIG. 28. 
 
 that there is more work in the construction of the higher 
 angle. The cost is consequently greater ; but when we 
 remember that the i-inch of 25 admits more light than the 
 one of 1 6, that it defines better, resolves 
 better, and proves to be a much superior 
 working glass in every respect, the 
 extra money will not perhaps be grudged 
 for it. 
 
 Half-inch objectives are made on two 
 systems : the low angles for binocular 
 use of a thick solid front, at the back 
 of which are two pairs of partly cor- 
 rected lenses, the aberrations being 
 finally corrected by the thickness of the 
 front. The higher angles are constructed 
 of three pairs of lenses, the posterior 
 combination being of considerable width. They are made 
 of as high an aperture as o'66 or 82 air angle, while the 
 A-ths of 100 air angle, or numerical aperture 0-76, is far 
 from uncommon. 
 
 E 2 
 
 FIG. 29. 
 
52 PRACTICAL MICROSCOPY. 
 
 The J-inch objective, yielding a power of 200 diameters 
 with the A eye-piece, is a most useful glass to the student, 
 when possessing an air angle of about 85. It is con- 
 structed of a triple back lens, a double 
 middle, and a single front. Messrs. Ross's 
 system is believed to differ from this, inas- 
 much as their objectives, from the J-inch 
 upwards, are supposed to be constructed on 
 Mr. Wenham's new formula, in which the 
 
 "" flint concave of a triple middle is made to 
 
 FIG. 30. 
 
 correct the aberrations of the anterior and 
 posterior crown lenses. An enlarged section of this formula 
 is shown in Fig. 31. 
 
 Quarter-inch objectives may be obtained of as high an 
 air angle as 140, very good for the experienced micro- 
 
 scopist but of limited use to the 
 
 student, as such glasses focus very 
 close to the object. 
 
 All objectives possessing a 
 numerical aperture of more than 
 / "v. 0*42 (50) should be furnished with 
 
 | a screw collar to adjust the lenses 
 
 ' for varying thicknesses of covering 
 
 FIG. 31. , , . . , , 
 
 glass, and this is specially needed 
 
 on Mr. Wenham's new formula. It is often a very tedious 
 operation to find the exact adjustment requisite ; but it may 
 be approximately performed in the following manner : 
 
 Set the collar at zero, and focus the glass upon the 
 object ; next turn the collar until the dust upon the cover- 
 glass is in focus, when an approximate correction will have 
 been applied ; if the observer again focusses by means of 
 the fine adjustment, the object will be found more sharply 
 defined than before. This may only be considered a rough 
 method. The best way is to work at some well-known 
 
AMPLIFYING POWER. 
 
 53 
 
 object, under varying positions of the screw collar, such as 
 Gyrosignia angulatum or the Podura scale, until the best 
 definition has been arrived at. 
 
 Under the denomination of high powers may be classed 
 all those yielding greater amplification than the J-inch. 
 They have become very common during the last few years, 
 nearly every maker of objectives issuing an " eighth," and an 
 immersion ^ or ^. 
 
 It appears probable that most of the high powers now 
 made are constructed upon a formula similar to that last 
 described by Mr. Wenham, and illustrated in .Fig. 31 
 (though this is denied by some makers), as he states most 
 distinctly that the formula is successful with all powers 
 requiring adjustment for cover-glasses, " from the J-inch 
 upwards." 
 
 Eighths and higher powers used to be specialities of the 
 first-class makers for which very high prices were charged ; 
 but now, for a student's general work, very good eighths 
 may be purchased for 50^., of an aperture of 0-82 (110) 
 and good working distance. 
 
 As to magnifying power, the annexed list has been ex- 
 tracted from the catalogue of Messrs. Powell and Lealand, 
 and will serve to show what degree of amplification is 
 yielded by the various objectives, in combination with 
 different oculars, at the recognised distance of 10 inches. 
 
 
 Objectives. 
 
 A. 
 
 B. 
 
 c. 
 
 D. 
 
 E. 
 
 
 
 inch. 
 
 
 
 
 
 
 
 
 4 
 
 12 
 
 18 
 
 25 
 
 50 
 
 75 
 
 
 
 2 
 
 25 
 
 37 
 
 50 
 
 IOO 
 
 150 
 
 
 
 I 
 
 50 
 
 74 
 
 100 
 
 200 
 
 300 
 
 
 
 
 
 100 
 
 148 
 
 200 
 
 400 
 
 600 
 
 
 
 
 ZOO 
 
 296 
 
 400 
 
 800 
 
 1,200 
 
 
 
 
 400 
 
 592 
 
 800 
 
 1, 600 
 
 2,4OO 
 
 
 
 
 800 
 
 1,184 
 
 1, 600 
 
 3,200 
 
 4,800 
 
 
 
 ^ 
 
 1,250 
 
 1,850 
 
 2,500 
 
 5,000 
 
 7,500 
 
 
 
 *v 
 
 2,500 
 
 3,7oo 
 
 5,ooo 
 
 10,000 
 
 15,000 
 
 
54 
 
 PRACTICAL MICROSCOPY. 
 
 It may be useful also to add a list of the magnifying 
 power of the oculars and objectives of Hartnack (now 
 Prazmowski) and of Zeiss. They are used in this country 
 to some extent, and the users always have the foible 
 of omitting the number of diameters to which the object 
 has been magnified, adding, however, the numbers of both 
 ocular and objective, to which the student generally has no 
 reference. It should not be forgotten that the amplifying 
 powers of the foreign objectives are calculated for a tube 
 of 153 millimetres (6 inches) in length, and most of these 
 objectives lose in their performance if employed in the 
 ordinary English length of tube. 
 
 Prazmowski (Hartnack) gives the following values for his 
 oculars and objectives : 
 
 Objec- 
 tives. 
 
 Oculars. 
 
 Equivalent 
 Focus in 
 Inches. 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 I 
 
 15 
 
 20 
 
 25 
 
 . , 
 
 
 
 2 
 
 2 
 
 3 
 
 4 
 
 25 
 
 
 
 g 
 
 70 
 
 45 
 80 
 90 
 
 120 
 140 
 
 
 
 I 
 I 
 
 I 
 
 100 
 
 150 
 
 "5 
 
 1 80 
 
 160 
 240 
 
 2 4 
 350 
 
 
 
 f 
 
 I 
 
 200 
 250 
 
 240 
 300 
 
 300 
 400 
 
 450 
 600 
 
 600 
 800 
 
 700 
 
 1000 
 
 I 
 
 9 
 
 350 
 
 400 
 
 550 
 
 860 
 
 IIOO 
 
 1400 
 
 A 
 
 IMMERSION OBJECTIVES WITH CORRECTION. 
 
 9 
 
 410 
 
 480 
 
 630 
 
 95 
 
 1300 
 
 ISOO 
 
 A 
 
 10 
 
 520 
 
 600 
 
 750 
 
 IIOO 
 
 1500 
 
 I800 
 
 A 
 
 13 
 
 820 
 
 95 
 
 1170 
 
 1700 
 
 2370 
 
 3100 
 
 A 
 
 15 
 
 1040 
 
 1200 
 
 1500 
 
 2200 
 
 3000 
 
 3600 
 
 A 
 
 18 
 
 1560 
 
 I800 
 
 2250 
 
 3300 
 
 4500 
 
 5400 
 
 A 
 
 Zeiss, whose objectives have been much in request during 
 the past year or more, is noted for great working distance ; 
 his angles are low and he designates his objectives by 
 
FOREIGN OBJECTIVES. 
 
 55 
 
 letters, but gives also the equivalent focal lengths in inches 
 and millimetres ; they are as follow : 
 
 
 
 
 O 1 
 
 Mark. 
 
 Equivalent 
 Focal Length. 
 
 Angular 
 Aperture. 
 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 
 inch. 
 
 mm* 
 
 o 
 
 
 
 
 
 
 
 ' aa 
 
 I 
 
 25 
 
 24 
 
 20 
 
 27 
 
 36 
 
 52 
 
 70 
 
 i 
 
 A 
 AA 
 
 | 
 
 15 
 15 
 
 24 \ 
 36 / 
 
 4 
 
 55 
 
 75 
 
 105 
 
 140 
 
 ~o 
 
 B 
 BB 
 
 | 
 
 10 
 10 
 
 40 \ 
 60 / 
 
 70 
 
 100 
 
 135 
 
 180 
 
 240 
 
 <u 
 
 r 
 
 C 
 CC 
 
 I 
 
 6-5 
 6'5 
 
 50 
 90 
 
 no 
 
 H5 
 
 195 
 
 260 
 
 370 
 
 i 
 
 D 
 DD 
 
 | 
 
 4'2 
 4*2 
 
 75 
 I0 5 
 
 175 
 
 235 
 
 320 
 
 440 
 
 600 
 
 
 E 
 
 | 
 
 2-8 
 
 no 
 
 260 
 
 350 
 
 480 
 
 660 
 
 900 
 
 
 i, F 
 
 A 
 
 1-8 
 
 no 
 
 410 
 
 550 
 
 75o 
 
 1020 
 
 1390 
 
 a ( G 
 
 i 
 
 3-0 
 
 i 
 
 250 
 
 340 
 
 45o 
 
 620 
 
 840 
 
 8 H 
 
 A 
 
 2'3 
 
 b 
 <U 
 
 320 
 
 440 
 
 590 
 
 800 
 
 IIOO 
 
 *g 1 T 
 
 %Z K 
 
 A 
 ft 
 
 1-7 
 1*3 
 
 g^ 
 
 bjO< 
 
 o 5 
 
 440 
 590 
 
 590 
 790 
 
 800 
 1060 
 
 1090 
 1450 
 
 1500 
 1980 
 
 Jsi L 
 
 A 
 
 I'O 
 
 ri 
 
 Q 
 
 760 
 
 1030 
 
 1380 
 
 1890 
 
 2580 
 
 H VM 
 
 55 
 
 o'75 
 
 w 
 
 IOIO 
 
 1360 
 
 1840 
 
 2520 
 
 3450 
 
 Equivalent focus of oculars, mm. 
 
 48 
 
 42 
 
 30 
 
 24 
 
 18 
 
 Do. do. in inches 
 
 1-88 
 
 i '64 
 
 1-18 
 
 "94 
 
 70 
 
 In the foregoing remarks it will be observed that 
 moderate angles have been advocated for students' use ; 
 but it must by no means be inferred that moderate angles 
 are the best. The higher the numerical aperture of an 
 objective, the nearer does the front lens approach the 
 object when in focus, and this has been urged as an 
 objection against the use of large apertures. There is 
 some force in this objection in dissecting, for instance, 
 it is absolutely necessary to have room underneath the 
 objective for the use of the various knives, needles, scissors, 
 and other instruments, which one cannot get with large 
 apertures ; but when the object has been prepared there 
 is no valid reason why the best lenses should not be used 
 for its examination. 
 
56 PRACTICAL MICROSCOPY. 
 
 Much has been said relative to the aperture of objec- 
 tives; therefore it may be of interest to the student to 
 know how the measurement of this angle may be set 
 about. Colonel Woodward and Mr. Wenham both prefer 
 modifications of Professor Robinson's method, as being the 
 most accurate. 
 
 Colonel Woodward screws the objective to be tested into 
 a tube, which pierces the shutter of his dark room, the 
 back of the objective being towards the light. A parallel 
 pencil of sunlight is then thrown through it by means of a 
 solar mirror, and the cone of light is measured off directly 
 upon a cardboard protractor, arranged with its centre in the 
 focal point of the lens. 
 
 Another method is to fix the microscope body so that it 
 may rotate upon a pin placed with the focal point of the 
 objective as a centre. This is then placed on a board 
 graduated into degrees, and the light of a candle, placed a 
 few feet off, viewed through the eye-piece. The body of 
 the microscope is turned until only half the field remains 
 illuminated, and the angle read off upon the graduated 
 circle below. Mr. Wenham declares this method faulty, 
 and also passes some strictures upon Colonel Woodward's 
 plan, stating that a border of diffused light exists which 
 renders the measurements inaccurate, the extreme angles 
 having often to be guessed at. 
 
 Dr. G. E. Blackham, in his paper already quoted, gives a 
 method suitable for most objectives, a plan which can easily 
 be carried out with one of the stands fitted with a swinging 
 substage. A plano-convex lens is employed, of such thick- 
 ness that when the plane side is connected with the under 
 surface of the object-slide with softened balsam, the thick- 
 ness of slide, balsam, and lens shall equal the radius of 
 curvature. This lens is connected by balsam to the under 
 side of the slide containing a balsam-mounted object. 
 
MEASURING APERTURES. 57 
 
 Dr. Blackham's lens is of crown glass, with a thickness 
 of 0-33 inch, and a radius of curvature of 0-45 inch. 
 
 The swinging substage bar is made to carry a small 
 candlestick, in which is placed a candle, so that when the 
 body of the microscope is horizontal, the light can be swung 
 round the object as a centre until either the image of the 
 object is imperfect or the centre of the field darkened. 
 
 In practice, the object (with the plano-convex lens 
 attached to the under surface of the slide) is laid upon the 
 stage and exactly focussed, the best definition being 
 obtained by use of the collar adjustment. If now the 
 angle that the most oblique ray makes with the optic axis 
 be measured, the angle of deviation in glass is obtained^ 
 from which the numerical aperture can be obtained by 
 simple inspection from the table given in Chapter V., and 
 the air or water angle quite as readily estimated. 
 
 Professor Abbe's apertometer will be described in 
 Chapter IX. 
 
CHAPTER IV. 
 ACCESSORIES. 
 
 HAVING made the reader familiar with the compound 
 microscope, its eye-pieces and objectives, we must now 
 consider those appliances which conduce 
 to excellence in microscopical examina- 
 tions, or which render the work more 
 easy and more quickly performed. It 
 must not be imagined, however, that the 
 possession of all the following accessories 
 is imperative for microscopical studies ; 
 far from it, as precisely the same effect 
 as that produced by the most costly ac- 
 cessory can often be obtained (with more 
 trouble) by very simple and inexpensive 
 means. 
 
 In the first place, we may consider the 
 draw-tube, which is shown in Fig. 32. It 
 is supplied of considerable length to most 
 monocular microscopes, being cut down in 
 many binoculars. 
 
 Into this draw-tube the eye-pieces 
 should be fitted, and the former then 
 becomes a means of increasing the ampli- 
 fying power of the combination. By 
 simply drawing out the tube the object is 
 thrown out of focus, and the objective has 
 to be carried nearer the object. This wonderfully alters 
 the relative distances of eye-piece and objective from 
 
DRAW-TUBE AND ERECTOR. 59 
 
 the object (conjugate foci), and the result is a considerable 
 increase in amplification. It must not be forgotten, how- 
 ever, that a limit will soon be found to this method of 
 increasing the magnifying power. The longer the tube, the 
 more of the periphery of the field will be cut off; and 
 further, the aberrations, which have been fairly corrected 
 for a moderate or short tube, may no longer obtain cor- 
 rection when the body of the microscope is unduly 
 lengthened. 
 
 Some of these tubes are plain, while others are divided 
 into inches and parts, so that results once obtained can be 
 recorded, if necessary. 
 
 There are many uses for the draw-tube, which the 
 student will be sure to find out for himself, and he will find 
 that if it is graduated, as shown in the figure, his work will 
 often be rendered much more easy. Some of 
 its uses will be found described under the 
 subjects of Dissecting and Micrometry. 
 
 Into the lower end of the draw-tube the erector 
 (Fig. 33) is made to screw. It consists of a tube 
 about 3 inches long, having a meniscus (concavo- 
 convex) at one end and a plano-convex at the 
 other, a diaphragm being placed about midway 
 between them. The convex side of each lens is 
 turned towards the eye-piece, this combination FlG 
 producing a second inversion of the image, so 
 that it is seen in its natural position. This is of great use 
 to the tyro dissector, as he has then but little difficulty in 
 the use of his dissecting instruments; but if any one 
 who has learned to dissect without it should attempt to 
 use the erector, he will find it is quite as hard to unlearn as 
 to learn. 
 
 The erector, when screwed into the lower end of the 
 draw-tube, enables the observer to employ a greater range 
 
60 PRACTICAL MICROSCOPY. 
 
 of magnifying power without changing the objective, and 
 this is especially useful in either dissecting or photography 
 by means of the microscope. 
 
 The field of view is also much increased, so that a very 
 large object can be included when using the half-inch objec- 
 tive, and by pulling out the draw-tube (containing the 
 erector, of course) a very considerable increase in amplifi- 
 cation is obtained ; thus, in the author's dissecting micro- 
 scope, when the erector is placed as near to the objective 
 as possible, the magnification obtained scarcely exceeds 
 8 diameters, while when the draw-tube is pulled fully out 
 the amplification is increased to 1 30 diameters. It should 
 be understood that the defining power of a microscope is 
 not increased by the addition of an erector. 
 
 The double nose-piece next claims our attention, and was 
 devised by Mr. Brooke for the purpose of quickly changing 
 
 FIG. 34. FIG. 35. 
 
 the objectives without the trouble of unscrewing and screw- 
 ing up again each time. This accessory is made in several 
 forms, but that shown in Fig. 34 is specially recommended, 
 the straight pattern being sometimes inconvenient, owing to 
 the one objective touching the stage before the other re- 
 quired for use is in focus. It is a very useful addition to the 
 
BULL'S-EYE CONDENSER. 
 
 6l 
 
 microscope, and should be purchased by all who can afford 
 it, when much work has to be done ; but on no account 
 should the beginner purchase one of those made to hold 
 three or four objectives they are too heavy, and often 
 nullify completely the action of the fine adjustment. 
 
 Some years ago Mr. Swift introduced a centering nose- 
 piece, which is shown in Fig. 35. In this accessory the 
 objective can be accurately centred after it has been 
 screwed into the nose-piece, which latter screws into the 
 lower end of the 
 body of the micro- 
 scope. The center- 
 ing screws are similar 
 to and act in the 
 same manner as those 
 connected with the 
 achromatic condenser. 
 Centering nose-pieces 
 are not very common ; 
 the author has seen 
 but one in use, and 
 that with high powers 
 only. 
 
 The student will 
 find the bull's-eye 
 condenser (Fig. 36), 
 or stand condenser, 
 as it is sometimes 
 called, a necessary ad- 
 junct, an instrument 
 which may be used 
 in a variety of ways ; but its proper use, and the methods of 
 illumination generally, can only be completely understood 
 by consulting a few diagrams of mirrors and lenses which 
 
 PIG. 36. 
 
62 PRACTICAL MICROSCOPY. 
 
 show their action upon various rays of light. An illustration 
 of the bull's-eye condenser is given at Fig. 36, from which 
 it may be understood that it is really a plano-convex lens of 
 crown glass, but mounted in various ways, and the student 
 should remember, on purchasing one, to select such a form 
 as may be turned and twisted in every desirable direction. 
 
 There are many uses for the bull's-eye condenser. It is 
 an indispensable instrument for the illumination of opaque 
 objects ; with it the microscopist is enabled to throw 
 parallel rays on to his mirror from the lamp ; he may use 
 it as a spot lens by fixing a small disc of dead-black paper 
 on the flat surface of the lens, and as an Amici prism for 
 the resolution of diatoms, Nobert's test lines, &c. 
 
 A smaller condenser, generally called a "condensing 
 lens " or " stage condenser " is supplied with some micro- 
 scopes, but its use is very limited, and the student is 
 advised to purchase only the independent stand condenser. 
 With the higher powers a more intense illumination can be 
 obtained by a combination of two condensers, the correct 
 method of using which may be made out by inspection of 
 the diagrams in the next chapter. 
 
 As to quantity of light, we have always found that 
 students have too much of it, and therefore it may be as 
 well to consider the diaphragm next. The diaphragm is 
 a thin plate of metal perforated with holes of various 
 shapes and sizes, and is used in order to cut off the super- 
 fluous rays from an object, or leading to an object, under 
 examination. At one time they used to be placed at 
 considerable distances beneath the object, but the practice 
 nowadays is to put them immediately beneath the slide, 
 which doubtless is their proper place. 
 
 The ordinary form is shown at Fig. 37, and is called a 
 wheel of diaphragms ; it is usually supplied to all student's 
 and third-class instruments. 
 
DIAPHRAGMS. 
 
 It is made of many degrees of excellence, and therefore 
 every cheap instrument purchased should be specially 
 examined with a low power (3 or 4-inch objective), to see 
 
 FIG. 37. 
 
 whether the apertures are concentric with the axis of the 
 instrument. Every part of the diaphragm should be well 
 blackened, in order to prevent the presence of reflected 
 light, which would interfere with the illumination. 
 
 Collin's graduating diaphragm, illustrated by Fig. 38, 
 was the first of its kind. It consists of four movable 
 shutters, acted upon by a lever, so that the whole of them 
 
 FIG. 39. 
 ^r 
 
 FIG. 38. 
 
 may be moved inwards or outwards simultaneously. The 
 opening thus produced is not circular, but this is of little 
 importance in actual working. 
 
 The graduating or " iris " diaphragm of Messrs. Beck is 
 illustrated in Fig. 39. It differs from that of Mr. Collins 
 only in the number of the shutters, which thereby produce 
 a nearly circular aperture. Mr. George Wale, of New 
 
6 4 
 
 PRACTICAL MICROSCOPY. 
 
 York, supplies a new form of iris diaphragm to all his 
 " working " microscopes. 
 
 It is now universally appreciated that the diaphragm must 
 be placed immediately beneath the object, in order to get 
 the best results. This has been attained by the " calotte " 
 
 diaphragms now made by 
 Messrs. Zeiss, Swift, and 
 others. This form is 
 placed over the achro- 
 matic condenser, on a 
 level with the stage, as 
 shown in Fig. 40 ; but the 
 simplest way to effect 
 this is by using a thin 
 plate of aluminium 3-inch 
 by I -inch, with the desired 
 aperture pierced in its 
 centre, and furnished 
 with two spring clips, so 
 
 that the slide may be placed upon it in any required posi- 
 tion, such as has been used by the author for the past 
 seven years. 
 
 There is another method of excluding the excess of 
 extraneous light, used by the author since 1873 with very 
 good results viz. that of slipping over the objective a 
 small perforated cardboard and aluminium nozzle, black- 
 ened inside, the central hole in the front being just a 
 trifle less than suffices to admit the rays passing from the 
 field of vision. 
 
 For many purposes it is necessary to concentrate the 
 light to a greater extent than can be done with a mirror 
 alone, and in such instances an achromatic condenser is 
 usually employed. This may be improvised from an 
 ordinary objective made to screw into an adapter below 
 
 FIG. 40. 
 
THE WEBSTER CONDENSER. 
 
 the stage, a ^-inch or ^-inch objective of wide angle 
 forming a very useful condenser. 
 
 A substage condenser consisting of a plano-convex lens 
 of j-inch focal length was used by Wollaston for illu- 
 minating the object upon the stage ; this was improved by 
 Goring, but still did not satisfy the requirements of micro- 
 scopists. In 1 840 the achromatic condenser was introduced, 
 and for many years afterwards continued to be made as a 
 low-angle objective, adapted in various ways to the stage 
 or substage. Whether 
 achromatic light for 
 illuminating purposes 
 is absolutely necessary 
 is a question we cannot 
 discuss here. 
 
 Messrs. Beck, Ross, 
 
 and Powell and Lea- 
 
 land, together with 
 other makers, have pro- 
 duced at various in- 
 tervals modifications 
 of the achromatic con- 
 
 FIG. 41. 
 
 denser ; but a departure from the usual custom was made in 
 1865 by Mr. Webster, who communicated a drawing of his 
 instrument to the pages of 'Science-Gossip/ and which 
 may be seen in Fig. 41. The diaphragm with which it was 
 furnished may be seen in Fig. 42. 
 
 Mr. Collins's " Webster " condenser is shown in Fig. 43, 
 and is a form extremely well-liked by all practical micro- 
 scopists ; it is made so that the diaphragm may be carried 
 quite close to the lens, and this can be further improved, 
 when dark-ground illumination is required, by placing a 
 circular piece of black paper on the lens itself. It can be 
 used with ease in combination with the polariscope. 
 
 F 
 
66 
 
 PRACTICAL MICROSCOPY. 
 
 The use of the condenser may be demonstrated in 
 various ways, but when employed in connection with the 
 diaphragm, one of its uses may be shown by taking a slide 
 
 FIG. 42. 
 
 of G. angulatum, and using the condenser with a small 
 central aperture. In this way it will be found very difficult 
 indeed to resolve the markings properly, but if the central 
 
 light be stopped out, so as 
 to utilise the oblique rays 
 only, the same effect will be 
 produced as by swinging 
 the mirror round to the 
 side and getting obliquity 
 in that way. 
 
 In using the achromatic 
 condenser, great care must 
 be taken to insure the co- 
 incidence of the optic axis with that of the microscope, 
 by manipulation of the two adjusting screws. This is 
 most easily accomplished by the use of the centering 
 
 FIG. 43. 
 
MESSRS. SWIFTS CONDENSER. 67 
 
 glass, made and sold by most opticians. The complete 
 condenser of Messrs. Swift and Son is a very ingenious 
 piece of apparatus ; it is made to supply the place of a 
 substage with all the ordinary compound substage ap- 
 paratus. It comprises an achromatic condenser with an 
 aperture of 140, a spot lens, a contracting diaphragm, 
 a revolving diaphragm and set of stops, polarising prism, 
 together with revolving mica and selenite films. The 
 polariscope is mounted on an eccentric arm, so that it can 
 be thrown in and out of use instantly, which is an important 
 feature, for it may be presumed that the polariscope would 
 be much oftener employed if it could be put in and out of 
 action as easily as shown in Fig. 44. 
 
 FIG. 44. 
 
 In the microscope itself Mr. Swift now inserts the 
 analysing prism of the polariscope in a brass box over 
 the Wenham prism, thus facilitating its use, as there is no 
 unscrewing of parts to fix the analyser in position. 
 
 Reade's double hemispherical condenser consists of a 
 
 F 2 
 
68 
 
 PRACTICAL MICROSCOPY. 
 
 plano-convex lens about ij inches in diameter, its flat side 
 being placed next to the object, and surmounted by a 
 smaller lens of the same form (hemispherical). A very 
 oblique illumination is possible with this condenser, and as 
 made by Messrs. Ross and Co. it is shown in Fig. 45. 
 
 Several makers are now producing oil-immersion con- 
 densers, in which the under side of the slide is connected 
 with the condensing lens by means of a film of castor oil, 
 oil of cedar wood, or glycerine. That made by Messrs. 
 
 FIG. 45. FIG. 46- 
 
 Powell and Lealand is shown in Fig. 46. It is not achro- 
 matic, but is able to utilise rays of 130 balsam angle. 
 Beneath the lens are fitted diaphragms of peculiar pattern, 
 and by its use the most difficult test objects may be re- 
 solved with the mirror in the optic axis of the microscope. 
 
 Messrs. Watson and Sons of Holborn produce an oil- 
 immersion condenser, in which the lens is mounted on a 
 plate of ebonite ; the object slide being placed above it, 
 the latter is held in position by a pair of clips, and is then 
 ready for examination. 
 
 The swinging substages of Messrs. Ross and Beck are 
 
THE TRAVERSING SUBSTAGE ILLUMINATOR. 69 
 
 useful for obtaining very oblique rays of light with the 
 help of the condenser. This has been accomplished in 
 another way by Messrs. Swift and Son, in their radial 
 traversing substage illuminator. While regretting that 
 this firm could not have found a shorter title for this acces- 
 sory, we must say it seems more generally applicable than 
 most other modes of producing obliquity of light. It is 
 shown in Fig. 47. 
 
 FIG. 47. 
 
 This apparatus has been constructed for the purpose of 
 increasing the resolving property of high-power objectives 
 by causing still more oblique pencils to impinge upon the 
 object than can be obtained by- most methods. The 
 arrangement consists first of an arc-piece, fixed below the 
 stage, radial to an imaginary line drawn through the axis 
 of the microscope objective, in the same plane with the 
 object. On this an achromatic condenser of special con- 
 struction is made to travel, thus keeping the rays of light 
 on the object during its entire traversing. These rays con- 
 verge and terminate in a focus through the front lens, in a 
 highly concentrated form. The condenser is illuminated 
 
70 PRACTICAL MICROSCOPY. 
 
 by a rectangular prism, for condensing light into the achro- 
 matic combination. The next part consists of a second 
 arc-piece placed at right angles to the former one ; this 
 also carries a similar achromatic condenser and illumi- 
 nating prism, which move radial to the centre. Both these 
 arc-pieces are so divided that each pencil of light can be 
 projected at a similar angle, and previous results can 
 always be recorded in the same way. Difficult test objects 
 are readily resolved, especially such diatoms as have rect- 
 angular striae or markings. With a -inch objective, the 
 diatom Navicula rhomboides is easily resolved into squares. 
 The markings on G. angulatum by the same means are 
 made to stand out in bold relief like half spheres. Those 
 usually considered easily resolvable only require one pencil 
 of light to show the markings. When this is the case, the 
 
 FIG. 48. 
 
 rectangular arc-piece with all its illuminating apparatus can 
 be turned away from the microscope stage as shown in 
 Fig. 48. The same illustration shows how opaque objects 
 may be illuminated, viz. by moving the condenser of the 
 first arc-piece above the stage of the microscope, when a 
 
MR. WEN HA M*S REFLEX ILL UMINA TOR. ^ I 
 
 pencil of light can be projected on to the object more perpen- 
 dicularly than with the bull's-eye condenser, thus preventing 
 shadows in coarse or deep objects which often produce dis- 
 tortion and false appearances. When the apparatus is 
 used for opaque objects with a lower power than the i-inch 
 objective, the achromatic combination can be removed and 
 the light directed from the prism, which can be made to 
 give convergent rays sufficient for use with a 4-inch 
 objective. 
 
 Wenham's reflex illuminator is valuable for use with 
 high powers ; but it possesses the disadvantage that all 
 objects for use with it 
 must either be selected 
 or specially mounted. It 
 has been described by the 
 designer at some length in 
 the seventh volume of the 
 ' Monthly Microscopical 
 Journal/ p. 237, in which 
 he states that by its use 
 the markings on A. pel- 
 lucida were brought out FlG 
 
 by an eighth objective, 
 
 which had never shown them before. Fig. 49 gives a 
 sectional . diagram of the illuminator, which has been 
 manipulated from Mr. Wenham's sketch. In using this 
 accessory, the glass cylinder is brought up level with the 
 stage, the centre of rotation is set truly by a dot on the 
 fitting, as seen with a low power. A drop of water is now 
 placed on the top of the cylinder, upon which the slide is 
 laid. The effect on the Podura scale is superb, the whole 
 surface appearing dotted with bright blue spots in a zigzag 
 direction. The plane mirror is the best for throwing up 
 the light, and when the finest effect has been obtained 
 
72 PRACTICAL MICROSCOPY. 
 
 upon any object, by simple rotation of the illuminator, an 
 exquisite unfolding of structure takes place. Objects on 
 the slide are brilliantly illuminated, while those on the 
 cover are nearly invisible. 
 
 Another illuminator has been devised by Mr. Wenham, 
 and is shown in Fig. 50. It looks very much like the 
 half of a broken button, which, never- 
 theless, collects and concentrates a sur- 
 prising amount of light. It consists of 
 a semicircular disc of glass J inch in 
 radius, the edge being well rounded and polished to a 
 transverse radius of ^ inch. This may be obtained from 
 Messrs. Ross and Co. and Messrs. Baker. 
 
 We have heard from several microscopists that they 
 have been unable to use this illuminator successfully, and 
 it has generally been the case where it has been mounted 
 for use in the substage. The best plan is to purchase the 
 article unmounted, and to make it adhere, for use, to the 
 underside of the slide, with a little glycerine and gum. 
 This illuminator does not require the addition of any 
 condensing lens, the necessary obliquity of light being 
 readily obtained by swinging the mirror to the side. 
 Mr. Wenham, in writing to the ' English Mechanic,' says 
 
 that while he was never success- 
 ful in the patient manipulation 
 required to bring out the striae 
 of Amphipleura pellucida, yet 
 with the new illuminator he 
 succeeded at once, and on every 
 subsequent occasion. 
 
 FlG The Amici prism ranks next. 
 
 It is made to exhibit one plane 
 
 and two lenticular surfaces, thus concentrating and reflecting 
 the rays at the same time. It is mounted so that it may be 
 
THE AMICI PRISM. 
 
 73 
 
 used in the substage, as shown in Fig. 51, or better 
 perhaps upon a separate stand, so that it is entirely inde- 
 pendent of the microscope or stage, Fig. 52. 
 
 In using this prism it is set beneath the stage at such a 
 distance from the axis of the microscope as to furnish rays 
 of sufficient obliquity, and in 
 order to produce the best 
 effect the stage should be 
 capable of rotating round the 
 fixed luminous rays, as with 
 line objects, such as the silici- 
 ous valves of diatoms, the 
 Navicula rhomboides, for in- 
 stance, there is nearly always 
 one position in which the 
 markings are shown to the 
 best advantage. 
 
 Colonel Woodward's prism 
 has been described upon p. 246, 
 vol. i. of the 'Journal of the 
 Royal Microscopical Society.' 
 It consists of a right-angle 
 prism of crown glass, the long 
 side of which measures J inch 
 by J inch wide ; it is cemented 
 into a base-piece of brass, 
 and supported on a stout 
 steel rod three or four inches long. Colonel Woodward 
 tells us that the whole apparatus ought not to cost 
 more than three or four shillings, but we are afraid he 
 has not consulted the optician in this matter. To use 
 it, the steel rod is slipped into a dark-well holder, and 
 putting a drop of oil on the upper face of the prism, it 
 is placed in contact with the under surface of the slide. 
 
 FIG. 52. 
 
74 PRACTICAL MICROSCOPY. 
 
 The light of a paraffin lamp is then to be condensed upon 
 the object through one of the faces of the prism, until it is 
 seen by inspection through the other face that the objective 
 is well illuminated. 
 
 Nachet's prism is shown in Fig. 53, the upper and lower 
 surfaces of which are convex, by reason of which the rays 
 of light proceeding from the mirror are con- 
 veyed by the lower surface, and after under- 
 going two reflections are finally brought to 
 a focus upon the object. The prism should 
 be so mounted that it may be revolved 
 for the same reasons as have been already 
 FlG - given when treating of the Amici prism. 
 
 The Nachet prism is not much used in 
 this country, and in its present form it is constructed with 
 the lower surface plane and not convex as in the original. 
 Then, again, there is the right-angle prism which finds 
 occasional use. The proportion of light reflected by a 
 prism is greater than can be obtained from the ordinary 
 plane silvered mirror, which always yields secondary 
 reflections from the surfaces of the glass. 
 
 Lord Osborne's illuminator or diatom exhibitor is made 
 by Messrs. Baker, of Holborn, and is much praised by many 
 microscopists as an aid in resolving markings on plane 
 surfaces ; it is somewhat similar to Reade's condenser in 
 the form of the lenses, but they are mounted differently. 
 
 The subject of condensers and prisms is one which 
 should be well studied by the beginner before he decides 
 to purchase ; always talk the matter over well with experts 
 before committing yourself to any particular form. 
 
 The illumination of opaque objects under high powers 
 has been attempted by many, but the most successful 
 appliances for this purpose are easily enumerated Powell 
 and Lealand's, and Beck's vertical illuminators, and Tolles' 
 
VERTICAL ILLUMINATORS. 
 
 75 
 
 interior illuminator. The best objects to show the method 
 of using these accessories the student will find to be the 
 Podura scale and the diatom Navicula rhomboides, or the 
 Amphipleura pellucida, which will be illustrated in the next 
 chapter. 
 
 Messrs. Powell and Lealand's vertical illuminator con- 
 sists of a highly polished plate of glass, set at an angle of 
 45 in an adapter which is screwed on over the objective. 
 There is an aperture in the side furnished with a revolving 
 diaphragm, through which the illuminating rays are made 
 to pass. These rays are reflected downwards, through the 
 objective, upon the object, as may be more easily under- 
 stood on reference to Fig. 54 a and b. 
 
 FIG. 54. FIG. 55. 
 
 Beck's vertical illuminator is very similar to the above, 
 but the plate of glass is replaced by a thin glass disc or 
 thin cover attached to a milled head, as shown in Fig. 55. 
 This seems to be a more handy form than the first, and for 
 ordinary instruments is perhaps the best. Still the author 
 must admit that with Messrs. Powell and Lealand's work- 
 manship their form of vertical illuminator is all that can be 
 desired. In December 1880, Mr. Powell exhibited at a 
 "Scientific evening" of the Royal Microscopical Society 
 Amphipleura pellucida lighted up with this illuminator, 
 
PRACTICAL MICROSCOPY. 
 
 and under their new twelfth objective the result was 
 superb. 
 
 This method of vertical illumination does not answer so 
 well with covered objects mounted dry ; there is a misti- 
 ness produced by the reflection from the covering glass, 
 while with objects mounted in balsam the illumination is 
 perfectly satisfactory. 
 
 The illuminator made by Tolles, and called the 
 " interior illuminator," may be seen in enlarged section at 
 
 Fig. 56. A prism is inserted 
 between the combination of 
 the objective, which collects 
 and throws down the light 
 through the objective on to 
 the object below. The curves 
 of the lenses figured form 
 that celebrated \ upon which 
 there was so much contro- 
 versy as to the real aperture 
 some few years since. 
 
 Another simple method 
 for illumination under high 
 powers was described by Mr. 
 James Smith at the March meeting of the Royal 
 Microscopical Society, 1880, extremely well suitable to 
 such objects as Podura scales, diatoms, &c., under powers 
 as high as the T^. 
 
 Mr. Smith uses the bull's-eye condenser only, and places 
 it with the plane side uppermost, just above the stage, 
 the lamp being set in front at a distance of two or three 
 inches. The light enters the condenser, and is reflected 
 very obliquely upon the slide from the plane surface of the 
 bull's eye. 
 
 An appliance often used to effect dark-ground illumina- 
 
 FIG. 56. 
 
SPOT LENSPARABOLOID. 
 
 tion is the spot lens : it is of very simple construction, 
 being a plano-convex lens, upon the upper flat surface of 
 which is drawn a circular spot of black varnish, so as to 
 exclude all central rays and prevent them passing into the 
 objective. It is shown in Fig. 57. 
 
 FIG. 57. 
 
 FIG. 58. 
 
 In the best instruments the paraboloid is the dark- 
 ground illuminator, as rays of greater obliquity can be 
 obtained by the use of this accessory than by the spot lens. 
 It is shown in Fig. 58. 
 
 In using the paraboloid the plane or flat mirror must 
 be used to throw parallel rays upwards, and these are 
 reflected from the internal 
 surfaces of the glass at such 
 an angle that with objectives 
 of moderate aperture the 
 field appears quite dark, the 
 rays simply illuminating the 
 object but not entering the 
 object glass. The track of 
 these rays may be seen on 
 reference to Fig. 59. 
 
 A central stop or dark 
 
 well is placed in the hollow 
 
 ? FIG. 59. 
 
 of the paraboloid, and is 
 
 capable of motion either upwards or downwards by means 
 
 of a pin which runs through a hole drilled in the glass ; 
 
78 PRACTICAL MICROSCOPY. 
 
 when this is pushed upwards it cuts off the less divergent 
 rays which would otherwise proceed from the apparatus. 
 When lamplight is used, the bull's-eye condenser should 
 be interposed between the lamp and the plane mirror, in 
 order to parallelise the rays which fall upon the latter. A 
 large mirror is requisite for the proper manipulation- of the 
 paraboloid, and this is not usually obtained in third-class 
 instruments. 
 
 When objectives of wide angle are used, a somewhat 
 different arrangement is necessary to secure dark-ground 
 illumination. In the ' Monthly Microscopical Journal ' for 
 
 July 1869, Mr. Wenham 
 reproduces the illumina- 
 tor which he first described 
 in 1856 as "A method 
 of illuminating opaque 
 objects under the highest 
 powers of the Micro- 
 scope." Fig. 60 will illus- 
 trate the subject of these 
 remarks. Cemented to a 
 
 glass slide with Canada-balsam is a nearly hemispherical lens 
 " with a segment removed so as to leave the thickness equal 
 to about one-third the diameter of the sphere. The circle 
 formed by the removal of the segment is blackened in order 
 to exclude all rays below the incident angle of total reflection. 
 This lens is intended to be used in conjunction with the 
 paraboloid as shown in Fig. 60. The rays pass through the 
 lens in a radial direction without refraction, and proceed 
 till they reach the upper surface of the thin glass cover, 
 where they are totally reflected upon the object." 
 
 An immersion paraboloid has since been devised by 
 Dr. Edmunds, and made by Messrs. Powell and Lealand ; 
 it is somewhat similar to the above in principle. 
 
PARABOLIC REFLECTOR LIEBERKUHN. 
 
 79 
 
 For the illumination of opaque objects several kinds of 
 apparatus are used, and of these we may consider first, the 
 parabolic reflector as made by several opticians. This is 
 most useful for low powers, from the 2-inch to the , and is 
 made to fasten on to the objectives by means of a spring 
 clip, so that it may slide up or down or be turned round to 
 secure the best illumination. 
 
 When this reflector is used with a lamp, the bull's-eye 
 condenser must be placed between them with the flat surface 
 towards the lamp, and its focal point 
 so adjusted that the rays emitted from 
 the bull's-eye shall be parallel. The 
 chief use of this reflector is to reflect 
 side light from all points of its surface 
 to a point situated on the plane of the 
 base in the focus of the objective. The form as made by 
 Messrs. Beck is illustrated in Fig. 61. 
 
 FIG. 61. 
 
 FIG. 62. 
 
 At A, B, C, and D, Fig. 62, are shown the accessories 
 called Lieberkuhns, or Lieberkuhn's reflectors, which are 
 used occasionally for the vertical illumination of opaque 
 objects. They are small silvered concave mirrors mounted 
 on short tubes, to admit of adjustment on the objective, 
 and thereby yielding the maximum illumination. A 
 separate Lieberkuhn is required for each object-glass, as 
 the focus of the concave mirror has to be adjusted to that 
 of the objective. 
 
 In using this appliance, parallel rays of light are thrown 
 
8o 
 
 PRACTICAL MICROSCOPY. 
 
 through the stage by means of the plane mirror, which on 
 meeting the Lieberkuhn are deflected upon the object, as 
 shown in Fig. 63. Lieberkuhns are not much used at the 
 present time, and can only be applied to objects which are 
 so mounted as to allow of the passage of marginal rays 
 through the slide. 
 
 FIG. 63. 
 
 FIG. 64. 
 
 Side reflectors, which are much used for the illumination 
 of opaque objects, are either mounted in the same manner 
 as stage-forceps, or as shown in Fig. 64, in a collar which 
 spans above the objective, as made by Mr. Swift. 
 
 The side reflector may be used to illuminate opaque 
 objects on the stage very successfully, and with such obli- 
 quity that many delicate markings which are unobserved 
 
DARK WELLSSTAGE FORCEPS. 8 1 
 
 with the Lieberkuhn are brought out without difficulty. In 
 use, the bull's-eye should be interposed between the reflector 
 and lamp, to render the light parallel, exactly the same as 
 with the parabolic reflector. 
 
 When the object is mounted on an ordinary slide, as a 
 transparent object, a dark ground may be produced by 
 using one of Lister's dark wells, which 
 are merely blackened stops, their deep 
 cup-shape insuring perfect blackness, 
 their diameter intercepting the rays 
 which would otherwise pass into the 
 objective. The engraving (Fig. 65) is 
 an illustration of a dark well in its sub- 
 stage mounting, as made by Messrs. 
 
 T> 1 
 
 Beck. 
 
 For these dark wells the author often uses small circles 
 of black paper mounted on the ordinary 3-inch by i-inch 
 slips, and for most purposes they answer admirably. 
 
 We now come to several very simple but important 
 additions to every microscope, the first of which is generally 
 supplied with all instruments. Fig. 66 delineates the stage 
 forceps, shown holding a fly for rough examination under 
 
 FIG. 66. 
 
 low powers. They are useful chiefly to beginners, with 
 such objectives as the 3-inch or 2-inch, but are altogether 
 unsuitable for high powers. 
 
 In the investigation of minerals it is often necessary to 
 examine small angular pieces which require to be viewed on 
 
 G 
 
82 
 
 PRACTICAL MICROSCOPY. 
 
 all sides. In order that this may be done easily, Messrs. 
 Beck make what is called a stage mineral-holder (Fig. 67), 
 one of the jaws being movable in a right line, so that it 
 may clamp any sized specimen, and by turning the milled 
 
 FIG. 67. 
 
 head of the jaw the mineral is made to revolve. Fig. 67 
 will perhaps show more clearly the action of this holder 
 than any description can do. 
 
 FIG. 68. 
 
 Morris's rotating stage (Fig. 68) often serves the purpose 
 of stage forceps. In its improved form it can be used for 
 both opaque and transparent objects. Small flies, larvae, 
 beetles, &c., can be affixed to the cork by means of a 
 small pin, or with gum, and as the stage moves upon a 
 secondary plate by means of a ball-and-socket joint, the 
 object can be placed in a variety of positions hardly 
 possible by any other means except the disc-holder of 
 Messrs. Beck. 
 
 Beck's disc-holder, shown at Fig. 69, is for the purpose of 
 holding for examination under the microscope the small 
 discs upon which objects have been temporarily or per- 
 
DISC HOLDER ROTIFER-TRAP. 83 
 
 manently mounted. The object is attached to the disc by 
 the aid of gum, or any other suitable adhesive material, 
 and when placed in the holder for observation, the disc can 
 be rotated in both 
 vertical and horizon- 
 tal directions. These 
 discs are very useful 
 for many objects, 
 especially those not 
 needing a cover, and 
 
 Messrs. Beck supply 
 
 ^ * FIG. 69. 
 
 boxes into which they 
 
 are fitted when not in use, so that they may be kept excluded 
 from the dust. 
 
 With many objects, in order to examine them minutely, 
 all that is necessary is to place them upon a glass slip, 
 add a drop of the right medium, and cover with a thin 
 covering glass. 
 
 This method of working is all very well for organisms 
 which are still, or comparatively so ; but when we come to 
 examine Rotifers, the Entomostraca, and other active forms 
 of life, we find means are required to keep them in one 
 position. Suppose, for instance, we wish to examine an 
 Entomostracon, which turns out to be Bosmina longirostris : 
 during its rapid motions through the water we would be 
 apt to come to false conclusions concerning it, but if we 
 prevent the organism from moving it can then be studied in 
 all its details. 
 
 The simplest and least expensive way of examining the 
 Infusoria and other moving micro-organisms is by the use 
 of the Rotifer-trap of Mr. F. Bedwell. This consists of a 
 few filaments of cotton wool placed upon the under glass of 
 a " live-box." The organism contained in a drop of water 
 is then run over it, and eventually becoming entangled 
 
 G 2 
 
8 4 
 
 PRACTICAL MICROSCOPY. 
 
 amongst the fibres, is kept comparatively still, by which its 
 form can be clearly made out. 
 
 Two forms of cages or live-boxes are shown in Figs. 70 
 and 71. They are, however, not all that can be desired. 
 Just so much pressure must be applied to the cap as is 
 
 necessary to keep the 
 animal still, and no more, 
 or it will be crushed and 
 distorted, so that the cap 
 requires much dextrous 
 manipulation. Often- 
 times such objects as 
 Entomostraca, &c., will 
 FIG. 70. not display themselves 
 
 to adVantage, so that the 
 
 cap requires loosening, to be again squeezed down at an 
 opportune moment. Moreover, it is generally found that 
 some particular organism will get near the periphery of 
 the cover, and in this all the interest may be concentrated, 
 
 yet the objective will 
 not reach it if it happens 
 to be of the form of 
 Fig. 71, and if we adopt 
 the form of Fig. 70 we 
 are often precluded from 
 using the achromatic 
 condenser to any portion 
 but the centre of the 
 slide. Instead of this 
 we may use the compressorium as made by Messrs. Beck, 
 Ross, Collins, and others, for use with high powers ; but 
 Piper's form, made by Mr. Swift, and illustrated in Fig. 72, 
 will be found more convenient. 
 
 The most delicate pressure can be applied by means of 
 
 1 
 
 FIG. 71. 
 
COMPRESSORIUM ZOOPHYTE TROUGHS. 
 
 these instruments, and all such intended for real use should 
 be reversible, so that the objects maybe easily viewed from 
 both sides, and this can be done with the form shown in 
 Fig. 72. 
 
 FIG. 72. 
 
 A form of compressor differing from all others has been 
 devised by Mr. Holman, U.S.A. ; the top or mica cover 
 is fixed while the lower thicker plate of glass is raised 
 or depressed by means of a screw-nut and spiral spring. 
 The employment of a thin mica cover is certainly an im- 
 provement, and one which English opticians would do 
 well to follow. In this we 
 imagine every practical 
 microscopist will concur, 
 as the breakage of a glass 
 cover in the middle of an 
 interesting observation is, 
 to say the least, vexing. 
 
 Zoophyte troughs may 
 be easily constructed by 
 the student ; the form 
 shown in Fig. 73 is made 
 
 FIG. 73. 
 
 of a thick glass base plate and ends, while two pieces of 
 thinner material furnish the front and back, which should be 
 of the same thickness as the thinnest slips are cut from. 
 This trough should measure T ^ of an inch in width, 
 
86 PRACTICAL MICROSCOPY. 
 
 2 inches in length, I J deep at the front, and 2 inches at the 
 back ; the base plate and ends being made from glass T % of an 
 inch in thickness and cemented together with marine-glue. 
 For higher powers, the form of trough shown in Fig. 74 
 is desirable. It consists of a glass slide, 3 x ij inches, 
 upon which is cemented with marine glue an ebonite or 
 glass semi-rectangular piece as shown in the figure ; the 
 
 half of a flat indiarubber 
 ring will answer admirably, 
 the front being formed of a 
 piece of thin glass. 
 
 In use, nearly fill the trough 
 with water, place it on the 
 FlG stage of the microscope, and 
 
 incline the body of the instru- 
 ment so that the observations may be made with comfort ; 
 adjust the lamp and concave mirror so that the most intense 
 and central light is thrown through the instrument; and 
 lastly, adjust the diaphragm until most of the marginal rays 
 of light are cut off, there remaining only just sufficient light 
 to work with. In all cases apply a larger aperture only 
 when absolutely necessary. 
 
 It may be here stated that the moderate use of the micro- 
 scope, either monocular or binocular, when employed in the 
 above manner, will not injure the eyesight of a healthy 
 person. When, however, an excessive glare of light is con- 
 stantly employed, the eye becomes less sensitive to ordinary 
 light; excess of illumination is a common fault with 
 beginners. 
 
 The several forms of zoophyte troughs such as those 
 shown in Figs. 73 and 74 may be obtained from any maker 
 or dealer in microscopic apparatus. 
 
 Fig. 73 is a wide trough, but it may be narrowed by 
 means of the wedge and spring, which drives a thin glass 
 
BOTTERILLS TROUGH AND LIFE-SLIDE. %7 
 
 partition close to the front plate; Fig. 74 is not adjustable, 
 but is easily made by the student. 
 
 Another adjustable form of trough is Botterill's, which 
 consists of two brass or ebonite plates bolted together, as 
 shown in Fig. 75, the plates of glass being separated, 
 according to the space required, by an ordinary indiarubber 
 ring of the requisite thickness. The trough can thus be 
 taken apart and the glasses cleaned, or a broken front 
 replaced without the trouble of cementing, the glass sides 
 being sufficiently thin to allow the use of high power 
 objectives. 
 
 FIG. 75. 
 
 A microscopic life-slide also devised by Mr. Botterill is 
 shown at Fig. 76 ; the advantages claimed for it are, the 
 facility with which it can be used and cleaned ; its reversi- 
 bility, allowing either side of the object to be examined 
 
 FIG. 76. 
 
 through thin glass ; the provision for renewing the supply 
 of water without disturbing any part of the apparatus, thus 
 enabling objects to be kept under examination for an 
 indefinite period ; the same arrangement also allowing of 
 
88 PRACTICAL MICROSCOPY. 
 
 the introduction of colouring matters, as carmine and 
 indigo ; and lastly, its moderate cost and durability. 
 
 For Confervae, small Infusoria, and similar organisms it 
 is sufficient to place the object on the bottom glass, with a 
 drop of water, and apply the covering glass in same manner 
 as when using a glass stage-plate. When a thicker layer of 
 water is required, a narrow ring of vulcanite, cork, or other 
 suitable material, of the requisite thickness, should be placed 
 on the lower glass, and the object put in position, the cover- 
 ing glass being finally applied as in mounting objects in a 
 cell. The supply of water can be maintained by putting a 
 drop occasionally in one of the side " wells," keeping the 
 slide, when not under examination, in a small damp cham- 
 ber, to prevent evaporation. To change the water, supply 
 through one "well," and draw out through the other by 
 means of a roll of blotting paper. 
 
 Messrs. Thompson and Capper, of Liverpool, were the 
 original makers of this slide, and also of BotterilFs zoophyte 
 trough, illustrated at Fig. 75. 
 
 The ordinary slip with a ledge of glass cemented to its 
 lower edge, as shown in Fig. 77, is very useful, and saves the 
 
 stage of the microscope 
 
 from corrosion when marine 
 
 . , . 
 
 organisms are being ex- 
 amined ; it may easily be 
 constructed by the student. 
 
 The glass for the construction of these troughs and slides 
 may easily be cut with a glazier's diamond, and the edges 
 ground parallel upon the flat face of an ordinary grindstone 
 kept well wetted with water, or even by rubbing them 
 upon a flat well-moistened piece of Yorkshire flagstone. 
 An emery wheel will also answer the purpose. Pieces of 
 superfluous glass may be removed by the use of a fine cut 
 file lubricated with oil of turpentine, and holes made with 
 
STEPHENSON'S SAFETY STAGE. 
 
 8 9 
 
 an ordinary drill lubricated with the same material. Glass 
 may be turned to any shape in the lathe by using a smooth 
 cut file, kept moistened with oil of turpentine, as the turning 
 tool ; but in order that this operation may be successful it 
 is necessary that the piece for turning be not of too large 
 diameter. 
 
 FIG. 78. 
 
 In working with high powers and expensive slides there 
 is often a risk of either one or the other getting damaged, 
 and this is especially the case 
 with immersion objectives, where 
 the kindly help of the dust on 
 the cover-glass is not obtainable. 
 It is never advisable to take high 
 powers or rare slides to conversa- 
 zione or other public meetings, 
 on account of the miscellaneous 
 character of observers ; but if such 
 a proceeding is imperative, the 
 exhibitor should certainly provide 
 himself with one of Stephenson's 
 new safety stages, shown in 
 Figs. 78 and 79, which may be the 
 means of saving him a few regrets. It is so constructed that 
 if by chance the object-glass is racked down on the thin cover, 
 
 FIG. 79. 
 
90 PRACTICAL MICROSCOPY. 
 
 no damage is done, on account of the object receding as 
 soon as contact is made, the springs shown in the figure 
 making that motion possible. The object is placed on the 
 two short arms C C, and is held in its place by the spring, 
 which is placed above and between them. In order to 
 make safety doubly sure Mr. Stephenson has devised a 
 second piece of apparatus to act with the former; it is 
 shown in Fig. 79, and consists of a square rod of brass which 
 
 FIG. 80. 
 
 must be adjusted to suit the various objectives used ; it is 
 held in its place by a pin passing through it, attached 
 to a screw at the outer side of the socket in which the rod 
 slides. This instrument is placed (in the Ross model) 
 beneath the bar which carries the microscope body, and, 
 when properly adjusted, allows the objective to touch 
 the object upon the stage, but arrests all further progress, 
 no matter with what degree of force the coarse adjustment 
 
MICROSCOPE LAMPS. 
 
 may be pressed, a property of considerable value to public 
 exhibitors. 
 
 Another very useful accessory is the revolving table, 
 several forms of which are now sold at a very cheap rate. 
 At one time the cheapest which could be obtained was 
 about 9/., and now they may be procured (with a slate top) 
 for less than one-fourth of that sum. 
 
 When two or more microscopists are pursuing any 
 investigation together, the constant rising from chairs must 
 often have been thought 
 a nuisance, but a cheap 
 revolving table enables 
 mutual observations to 
 be made with comfort. 
 The author's revolving 
 table is 2 feet 4 inches 
 in diameter, the top of it 
 is 2 feet 3 inches from the 
 ground, and four or even 
 six observers may com- 
 fortably sit round it. 
 
 And now a few words 
 as to illuminating ap- 
 paratus. The best light 
 which can be obtained 
 is that from a good white 
 cloud on a sunny day, 
 but unfortunately in our 
 towns and crowded cities 
 we get but little sun- 
 light undiluted with smoke, and students generally are 
 occupied the day through, so that it becomes necessary to 
 use artificial light. 
 
 When using light from the sky or from the sun, it should 
 
 FIG. 81. 
 
9 2 
 
 PRACTICAL MICROSCOPY. 
 
 be remembered that the rays are, for all practical purposes, 
 parallel, and thereby differ essentially from artificial light, 
 the rays of which converge strongly from the luminous 
 centre. For use at home there is nothing, perhaps, so 
 convenient as an argand gas reading lamp, sliding up and 
 
 down on a metal rod, 
 with a shade over it 
 to prevent extraneous 
 light from reaching 
 the eyes. Students 
 are very apt to work 
 with too much light, 
 and thereby impair the 
 sensitiveness of their 
 eyes ; they should 
 endeavour, however, 
 to work with only just 
 as much light as is 
 necessary to bring 
 out plainly the details 
 of the object under 
 examination, and no 
 more. 
 
 If an oil lamp is 
 desired, a very com- 
 mon one maybe made 
 to answer almost 
 every ordinary pur- 
 pose, provided it is low enough, as when it is required to be 
 raised, that may be readily accomplished by means of 
 blocks of wood of varying thickness. The ordinary form of 
 microscope lamp is shown in Fig. 8 1 ; it differs slightly in con- 
 struction in the hands of different makers, but the student 
 should eschew all forms in which the oil reservoir case is 
 
 FIG. 82. 
 
MR. SWIFTS MICROSCOPE LAMP. 
 
 93 
 
 soldered to the sliding ring ; all the author has seen from 
 different makers have come to pieces in a very short time. 
 Browning's oil lamp, with bull's-eye condenser and silvered 
 reflector, is shown at Fig. 82. It has a porcelain shade 
 covering the chimney to protect the eyes from the excessive 
 glare. This lamp (and in- 
 deed most oil lamps) is used 
 with paraffin oil, and the 
 brilliancy of the light may 
 be increased by dissolving 
 a little camphor in it. The 
 light is more intense when the 
 edge of the flame is turned 
 towards the object to be 
 illuminated ; but if quantity 
 of light is required rather 
 than intensity, the flat side 
 of the flame may be so 
 disposed. 
 
 A rather better lamp than 
 the above for general work is 
 that of Mr. Swift, and shown 
 in Fig. 83, which, however, 
 in the writer's estimation, 
 would be much improved by 
 a glazed porcelain chimney 
 with two opposite perfora- 
 tions, for in most examina- 
 tions (perhaps all) it is a very important point to avoid a 
 flood of extraneous light passing to the eyes. 
 
 There are several other lamps which may be mentioned 
 here : Collins's Bockett lamp and Fiddian's lamp, made by 
 Messrs. Ross and Co. The Fiddian lamp is supported by a 
 massive claw stand, from which rises a vertical support on a 
 
 FIG. 83. 
 
94 
 
 PRACTICAL MICROSCOPY. 
 
 ball-and-socket joint. A brass tube slides on the vertical 
 rod bearing the condenser and lamp with neutral tint shade 
 and " white cloud " reflector having telescope and clamping 
 screw adjustments. When these are placed in any desired 
 relation to each other, the whole can be vertically adjusted 
 by a rack and pinion with the greatest accuracy. Its price 
 
 is five guineas. Another 
 beautiful lamp has been 
 made by Messrs. Wood, of 
 Liverpool, for Messrs. Dallin- 
 ger and Drysdale. These 
 two observers, whilst work- 
 ing at the life-history of the 
 monads, appreciated the diffi- 
 culty of accurately centering 
 the image of the flame when 
 working with the Jy and ^ 
 objectives, and so devised 
 this lamp, which is illustrated 
 in the April number of the 
 'Monthly Microscopical 
 Journal' for 1876, vol. xv. 
 
 Parkes' microscope lamp 
 with cooling evaporator may 
 be seen in Figs. 84 and 85. 
 
 C is a bronzed copper cylin- 
 FIG. 84. , . . , , , ' 
 
 dncal shade 3^ inches m 
 
 diameter with a hood at the front to prevent the upward 
 reflection of light. At the back is a parabolic reflector 
 transmitting nearly parallel rays, made removable for the 
 purpose of cleaning. At the front is a tinted " light-modi- 
 fier," secured by a bayonet joint, and may be also removed 
 when desirable. D is the " cooling evaporator " ; a layer of 
 thick felt is placed inside for saturation. When the lamp is 
 
PARKED MICROSCOPE LAMP. 
 
 95 
 
 lighted, this vessel is filled with water, and so prevents the 
 radiation of heat upon the observer's head. The felt requires 
 moistening about once every five hours. 
 
 The light of the sun, a white cloud, or the electric light, 
 which the author has used, and will illustrate in a future 
 chapter, each give a light of remarkable purity. This is 
 not the case, however, with the light from gas or from oil 
 lamps. These last, especially gas 
 sources of illumination, give a very 
 objectionable yellow tone, while 
 some tints are nearly suppressed. 
 This effect has been noticed by all 
 observers, and in 1872 Mr. Collins 
 produced a light-corrector, and 
 exhibited the same at a soire'e at 
 the Quekett Club. It consists of a 
 brass stage-plate with a groove in 
 which rotates a diaphragm of 4 
 apertures one open, one fitted with 
 a finely ground glass, while the 
 others are fitted with two different 
 tints of blue. Rainey produced a light-modifier before 
 this, but it was of such construction that it required 
 fitting to each microscope; that of Mr. Collins, on the 
 other hand, can be used with any instrument, and without 
 fitting. 
 
 The effect of the blue glass is to effectually correct the 
 yellowness proceeding, from all artificial illumination, 
 rendering the light soft and agreeable, as well as to im- 
 prove the definition. To produce this effect, the writer 
 uses a simple 3 in. x i in. slide of blue glass, such as is 
 used by the chemist for the qualitative analysis of potash 
 salts. It was obtained from Messrs. J. J. Griffin and Sons, 
 Garrick Street, Covent Garden. 
 
 FIG. 85. 
 
96 PRACTICAL MICROSCOPY. 
 
 Dr. Woodward prefers to use the ammonia-sulphate of 
 copper cell, and then only for high power definition, and he 
 says he has been able to resolve the markings on Amphi- 
 pleura pellucida with objectives found incapable of doing it 
 with white light. Professor Smith, of Ashtabula, also 
 expresses his approval of the use of monochromatic light. 
 He says that with its use, and an eighth dry objective, he 
 has easily resolved the A. pellucida to beads, in balsam, 
 with deep eye-pieces ; and with the lowest eye-piece the 
 transverse and longitudinal striae were easily seen. 
 
 The white cloud illuminator is a contrivance made in 
 order to produce the same kind of illumination from 
 artificial light as is obtainable from a white cloud. It is 
 generally used with low powers only, and is made in 
 several ways a concave surface of plaster of Paris, a 
 mirror coated at the back with zinc-white paint, roughened 
 enamel, and white paper have all been used to produce 
 this effect, as well as the disc of ground glass found in 
 Mr. Collins's light-modifier. 
 
 Thus closes the chapter on accessories; but the student 
 must not think we have exhausted the subject : there are 
 many pieces of apparatus in occasional use which it has not 
 been thought necessary to include here, and many others 
 will be described in the subsequent chapters under the 
 headings in which they are more intimately concerned. 
 
CHAPTER V. 
 
 GENERAL REMARKS UPON OBJECTIVES TEST OBJECTS. 
 
 WHEN we consider the many adjustments of apparatus 
 needed ere a correct picture of an object can be placed 
 before the eye, it will be readily seen how necessary it is to 
 pay strict attention to details more especially of illumina- 
 tion, this being one of the first and most important lessons 
 the microscopist has to learn. 
 
 When rays of light pass through media with parallel 
 faces, such as the glass slips used by every worker with the 
 microscope, the emerging rays are parallel with those enter- 
 ing, the intermediate portion being bent away from both 
 these planes as shown in Fig. 86. If water be used above 
 the glass, the emergent ray will be bent up more towards 
 the perpendicular, while when cedar-wood oil, or any of the 
 homogeneous-immersion fluids are employed, the path of 
 the ray will be one continuous 
 line from the under side of the 
 glass slip. A diagram of the 
 passage of a light-ray through 
 glass is shown in Fig. 86. 
 
 Ordinary glass slides, and also 
 
 the thin covers, are made from 
 
 FIG. 86. 
 crown glass having a refractive 
 
 index varying from 1-5 to 1*525 referred to air as unity: 
 the following table of mean refractive indices of many sub- 
 stances used by the microscopist may not be uninter- 
 esting : 
 
 H 
 
PRACTICAL MICROSCOPY. 
 
 REFRACTIVE INDICES. 
 
 Air ................ I'ooo 
 
 Water ................ -336 
 
 Sea water .............. -343 
 
 Alcohol .............. -373 
 
 Glacial acetic acid .......... '380 
 
 Equal parts, glycerine and water . . . . ' 400 
 
 Glycerine .............. '475 
 
 Oil of turpentine ............ 478 
 
 Crown glass ............ I 5 to 525 
 
 Homogeneous-immersion fluid ...... 500 
 
 Chloride of cadmium in glycerine . . . . ' 500 
 
 Cedar- wood oil ............ '512 
 
 Canada balsam ............ -532 
 
 Flint glass .............. -575 
 
 Monobromide of naphthaline ...... '658 
 
 Bisulphide of carbon .......... '678 
 
 Oil of anise .............. i'8n 
 
 Sulphur .............. 2*115 
 
 Phosphorus .............. 2-224 
 
 Plane or flat mirrors reflect an image of the same size as 
 the object, the flame of a gas or oil lamp for instance, and 
 therefore the rays are parallel, and the image is not inverted. 
 When light is reflected from glass, the under side of which 
 is silvered, much of it is lost from several causes ; but when 
 polished metal is employed for the reflecting surface, the 
 rays do not enter the substance of the reflector, and there 
 is less loss of light than in the former instance. 
 
 We must now turn our attention to the concave mirror, 
 with which all respectable microscope stands are furnished. 
 In this kind, the focus is situated at a point at which the 
 reflected rays meet, and when rays parallel to the axis are 
 brought together after reflection, the meeting point or focus 
 is at an equal distance between the centre of curvature C 
 and the mirror itself, and, consequently, if a luminous object 
 be placed in this principal focus F, the rays emitted by the 
 whole surface of the mirror will be parallel, as seen in 
 Fig. 87. 
 
 If, however, the luminous point be at a greater distance 
 
CONCA VE MIRRORS. 
 
 99 
 
 from the mirror than the principal focus, or vice versd if the 
 luminous rays fall divergent upon the concave mirror, a 
 focus is obtained at another point called the conjugate focus. 
 In the first case the rays, instead of being parallel, will 
 converge towards L (Fig. 88), while in the second the focal 
 
 FIG. 87. 
 
 point of light will be removed further away from the mirror, 
 and the rays proceeding from a lamp may be brought to a 
 focus until the distance between the source of illumination 
 and the mirror has been lessened to the centre of curvature, 
 the rays being then reflected on to themselves. 
 
 FIG. 88. 
 
 FIG. 89. 
 
 If the source of light be placed between the principal 
 focus and the mirror the reflected rays will be divergent, as 
 shown in Fig. 89. 
 
 Let us now consider the action of lenses upon illuminating 
 rays. In a double convex lens the refracted rays from a 
 parallel pencil of light form a focus very near to the centre 
 of curvature of the lens, and conversely when a lamp is 
 placed in its principal focus a double convex lens may be 
 made to appear the source of light, as shown in Fig. 90. 
 
 H 2 
 
100 
 
 PRACTICAL MICROSCOPY. 
 
 It will be seen that a double convex lens has a principal 
 focus on either side of it, and therefore the light may be 
 parallelised on either side, but if the source of illumination 
 be placed further away than the principal focus, the rays 
 
 FIG. 90, 
 
 will be no longer parallel, but centred in a point at some 
 distance from the opposite side of the lens, as shown in 
 Fig. 91. 
 
 FIG, 91. 
 
 These points (/ and L) are called conjugate foci, and do 
 not lie in any fixed plane, but are dependent the one upon 
 the other; it is this movement of the conjugate foci which 
 yields a long working distance from the objective when the 
 body of the microscope is shortened, and requires the 
 object-glass to be approached nearer to the object when 
 the draw-tube is used. 
 
 Diverging rays can be produced by placing the illumi- 
 nating point between the principal focus and the lens, and 
 
THE PLANO-CONVEX LENS. 
 
 101 
 
 when converging rays fall upon a double-convex lens they 
 are brought to a focus at a point between the principal 
 focus and the lens itself, as shown in Fig. 92. 
 
 The action of a plano-convex lens, of which our bull's-eye 
 condenser, Fig. 36, is a type, may be studied in the same 
 diagrammatic man- 
 ner. This may be 
 considered as a 
 double-convex lens 
 split down the centre, 
 and so forming two 
 plano-convex lenses ; 
 it is generally used 
 for purposes of microscopy on account of the great work- 
 ing distance of its focus. As already described, parallel 
 rays falling upon a double-convex lens come to a focus 
 very near the centre (radius) of its curvature, but when 
 the same rays fall upon the curved surface of a bull's-eye 
 condenser they are brought to a focus at a distance equal to 
 the diameter of the curvature, or twice the distance of a 
 double-convex lens, as may be seen in Fig. 93 ; and con- 
 versely if we wish to produce rays of parallel light from 
 
 FIG. 92. 
 
 FIG. 93. 
 
 a lamp, the ordinary bull's-eye condenser must be placed 
 twice as far from the luminous point as would be neces- 
 sary in the case of a double-convex lens, a condition of 
 
102 PRACTICAL MICROSCOPY. 
 
 extreme importance when we consider the heat given out 
 during combustion in most oil lamps. 
 
 These remarks upon the behaviour of certain lenses and 
 mirrors towards the rays of light may be considered super- 
 fluous, nevertheless, as the student proceeds, he will find 
 that not one word too much has been written. False 
 appearances are often produced by the bad employment of 
 light, and the student is advised to practise many kinds of 
 illumination upon objects with which he may be familiar, so 
 as to acquaint himself with the various appearances which 
 diverse applications of it will afford. 
 
 When the action of the various mirrors and lenses has 
 been fairly grasped, the student should proceed with some 
 work capable of giving him experience of the manner in 
 which various objects are delineated or depicted under 
 various objectives. In the days of Dr. Goring (1832) when 
 objectives even of high amplification had not surpassed an 
 air angle of 55, and even when achromatics were despised 
 by nearly all working microscopists, it would not have been 
 a difficult task to test an objective for its spherical and 
 chromatic aberrations, by means of the tests we now possess ; 
 but time has changed all things microscopical ; really bad 
 lenses are rarities, and taking objectives to, and including 
 the -inch, it is remarkable how few imperfections they 
 possess. 
 
 In order to correct perfectly the aberrations of objectives, 
 the practical optician employs the globule of mercury or 
 "artificial star" as a test object, while the accuracy of their 
 setting is examined by studying the reflected image of a 
 flame or the window bars, while the mount with lenses 
 in situ is revolving in the lathe. 
 
 Beyond mention of it, the " artificial star " test need not 
 be described here; it has been fully treated upon by 
 Dr. Goring in the 'Microscopic Cabinet/ to which the 
 
WORKING DISTANCE. 103 
 
 reader is referred, while the introduction of a good series 
 of test objects renders the general employment of the 
 former scarcely necessary. 
 
 It must not be forgotten that great differences exist 
 between test objects. Amongst the slides of Pleurosigma 
 angulatum, sold for this purpose, some are so extremely 
 coarse as not to be a test in any sense of the word, while 
 others are so finely marked that they can only be resolved 
 with the greatest difficulty under a J-inch objective of high 
 air angle. This is also the case with the diatoms Navicula 
 rhomboides and A mphipleura pellucida, used as tests for the 
 highest powers ; so that no reliance should be placed upon 
 statements that such and such a diatom was resolved 
 under a certain objective. 
 
 Object-glasses for use with the microscope are usually 
 spoken of as possessing the following qualities : 
 
 1. Working distance of the front lens from the object ; 
 
 2. Defining power ; 
 
 3. Flatness of field and freedom from distortion ; 
 
 4. Penetrating power ; 
 
 5. Resolving power ; 
 
 and it is to ascertain their excellence, or otherwise, 
 in these directions that test objects are brought into 
 use. 
 
 WORKING DISTANCE. It has already been shown that 
 the nomenclature of objectives does not presuppose any 
 working distance from the front lens ; in fact, such a thing 
 would be impossible, seeing that the enlargement of the 
 aperture reduces the distance of the front lens from the 
 object, while the amplification remains the same. Their 
 designation, such as a " i-inch objective," indicates only that 
 such an object-glass should possess the same magnifying 
 power as a single lens of i-inch focus, the distance the 
 
104 PRACTICAL MICROSCOPY. 
 
 front of the system focusses from the object not being 
 considered at all. 
 
 Gundlach, in a rather abstruse article in the 'American 
 Monthly Microscopical Journal,' ii., 1881, tells us that 
 "working distance" depends upon (i) the focal distance 
 (nominal, it is presumed), (2) the aperture, (3) the number 
 of lenses of which the objective is composed, (4) the pro- 
 portionate curves of the lenses, and (5) the thickness of 
 the lenses. 
 
 Great working distance is valuable in an objective only 
 when circumstances demand it. Thus, for dissecting, or for 
 the examination of opaque objects, a certain amount of 
 distance is requisite for manipulation and illumination ; but 
 when an object has been prepared and mounted, no more 
 working distance is absolutely required than will admit of 
 the use of the thickest covering-glass, and of the examina- 
 tion of a moderate depth of object. 
 
 High-angle objectives of low power and consequent 
 shorter working distance will define much better than the 
 smaller apertures, and there is sufficient working distance, 
 even for dissecting, with the i-inch of 25 air angle. 
 
 There is some difficulty in selecting a i-inch objective. 
 A glass of 40 air angle possesses considerable working 
 distance, being a power well suited for dissections, used in 
 conjunction with the erector ; while a J-inch objective of 
 80 air-angle scarcely gives o 03 inch of working distance, 
 focussing closer to the object than an ordinary J-inch objec- 
 tive of 85. 
 
 With the i-inch and all higher powers the working 
 distance is very small, so that often the microscopist is 
 precluded from using covering-glasses of the ordinary 
 thickness. This is the case with all extremely high aper- 
 tures used as dry objectives. Immersion objectives, for 
 the same degrees of amplification, afford much longer 
 
DEFINING POWER. 
 
 105 
 
 working distances than dry lenses, so that it is often pos- 
 sible to use an immersion ^-inch where the covering-glass 
 is too thick for a dry Jth. 
 
 The author would like to see objectives catalogued by 
 the makers in somewhat the following manner ; the oculars 
 too might be included : 
 
 Designation. 
 
 Aperture. 
 
 At 10 inches 
 with A ocular. 
 
 Price, 
 
 Remarks. 
 
 Numerical. 
 
 Air angle. 
 
 Working 
 distance. 
 
 M 
 
 a 
 II 
 
 I -inch 
 ^-inch 
 
 1-inch 
 ^2 -inch 
 
 0*64 
 
 0*94 
 
 I*OO 
 
 16 
 
 25 
 40 
 60 
 
 8 o 
 
 140 
 180 
 
 0-750 
 O*42O 
 0*300 
 0*I50 
 0*032 
 0*080 
 0*038 
 0*024 
 O*OO7 
 
 50 
 56 
 100 
 
 106 
 no 
 
 200 
 2IO 
 
 600 
 6l 5 
 
 * 
 
 Triplet. 
 Dry objective. 
 
 > > 
 
 Water-immersion. 
 ) Homogeneous- 
 ) immersion. 
 
 Oculars 
 
 A or I 
 
 Bor2 
 
 C or 3 i D or 4 
 
 Eor 5 
 
 For 6 
 
 Amplifying power) 
 in diameters / 
 
 5*0 
 
 rs 
 
 I0'0 
 
 20-0 
 
 30*0 
 
 40*0 
 
 DEFINING POWER. This property is of the first import- 
 ance in objectives, and has been described by Dr. Goring 
 to mean " nothing more than a destitution of both kinds of 
 
 FIG. 94, 
 
 aberration." A well-corrected objective focusses the indi- 
 vidual rays of a pencil of light, both from the centre and 
 periphery, to the same plane as shown at F in Fig. 94 ; but, 
 nevertheless, a more or less distinct image is produced for 
 
io6 
 
 PRACTICAL MICROSCOPY. 
 
 some distance from each side of this focal plane. If, how- 
 ever, the rays are not thus corrected, the outlines of edges 
 of the image will be thick and confused, and the glass is 
 said "to be wanting in definition." 
 
 This fault may be shown diagrammatically in Fig. 95, 
 which is an under-corrected glass, the peripheral rays being 
 
 FIG. 95. 
 
 brought to a focus at ///, between the central focus F and 
 the lens itself. Lenses in their primitive state are very 
 much " under-corrected," and can only be employed when 
 it is possible to cut off the peripheral rays by a diaphragm. 
 An over-corrected lens is shown in Fig. 96, from which it 
 may be seen that the marginal rays are thrown further away 
 from the glass, being brought to a focus at /// respectively, 
 while F represents the focus of the central portion. 
 
 FIG. 96. 
 
 An objective free from both these defects is said to be 
 free from spherical aberration or aplanatic. 
 
 These defects in cheap low-angle objectives are corrected 
 (if the term will apply) by the interposition of a diaphragm 
 behind the back lens cutting off the marginal rays. These 
 rays cannot then enter into the formation of the picture, 
 the result being a dark, not very well defining glass of 
 
DEFINING POWER. 
 
 107 
 
 low angle, but long working distance, though not suffi- 
 ciently corrected to work with deep eye-pieces. In the best 
 objectives of high angle the marginal rays are not cut off, 
 but corrected to the very edges by the application of a 
 wider back lens than usual ; the aperture is therefore larger, 
 but the objective possesses less penetration than one of 
 lower aperture, and the working distance has been materially 
 reduced. 
 
 A small aperture objective may be constructed from 
 one of these more perfectly corrected lenses by the addition 
 of a diaphragm ; such an objective would bear deep eye- 
 pieces and possess a fair amount of penetration, though the 
 working distance may not be sensibly increased, owing to 
 the thickness of the lenses and their various curves not 
 being specially planned with this end in view. 
 
 The defining power of an objective may be examined by 
 the employment of certain test objects obtainable from 
 Messrs. Norman or 
 Wheeler, until the 
 student has learned how 
 to prepare them for 
 himself. The pollen of 
 the Hollyhock (Althea 
 rasa), shown in Fig. 97, 
 is a useful test ; it must 
 be illuminated as an 
 opaque object, and with 
 a deep eye-piece (the 
 Huyghenian D), the 
 minute spines should 
 be readily and clearly 
 defined. 
 
 A well cut wood-section, such as is shown in Fig. 98, is 
 also an excellent test of definition, the borders of each 
 
 FIG. 97. 
 
io8 
 
 PRACTICAL MICROSCOPY. 
 
 vessel and cell should be clearly and sharply delineated, 
 there must be no mistiness or blackness of edge. A dark 
 
 FIG. 98. 
 
 image shows at once that too much of the peripheral 
 pencil has been cut off, the definition of a small aperture 
 
 objective being never equal 
 to one" of large angle. 
 The figure shows a sec- 
 tion of the Horse-chestnut 
 stem (^Esculus hippocasta- 
 num). 
 
 Triplets, such as are 
 shown in Fig. 28, gene- 
 rally break down under 
 deep eye-pieces. 
 
 The proboscis of the 
 Blow-fly, shown in Fig. 99 
 a favourite preparation 
 of the late Mr. Topping 
 is an excellent object for 
 testing the defining power 
 of an objective of low 
 amplification ; the outlines 
 
 may be fairly sharp, yet the details of the pseudo-tracheae 
 will not be clear, well defined, and free from colour under 
 
TESTS OF DEFINITION. 
 
 109 
 
 a deep eye-piece, unless the corrections have been well 
 cared for. 
 
 The student should, if possible, compare this object under 
 two objectives, one of foreign make yielding an amplifica- 
 tion of 50 diameters with the A eye-piece, the other a i-inch 
 of English construction, possessing an air angle of 30. 
 
 Another exceedingly good test of definition is a well 
 mounted specimen of the tracheal system of Dytiscus 
 marginalis, delineated in Fig. 100. 
 
 In this instance the spiral threads should be visible with- 
 out any halo of colour, and clearly separated so as to appear 
 a continuous fibre 
 rolled between two 
 membranous walls. 
 
 The engraving 
 shows the illusive ap- 
 pearance generally 
 perceived in this ob- 
 ject that of watered 
 silk produced by 
 the contact of the 
 back and front of the 
 spiral, at different in- 
 clinations, when the 
 object is flattened and 
 mounted in the usual 
 way in balsam. 
 
 In order to discover how the correction for colour has 
 been performed, several objects may be employed ; Dr. 
 Carpenter's test is the section of pine-wood shown in Fig. 
 101 ; it should be mounted dry, and the small circles 
 (glandulcz) must be well defined and free from colour 
 even with the D eye-piece. Perhaps absolute freedom 
 from colour under deep eye-pieces does not yield the 
 
 FIG. 100. 
 
1 10 
 
 PRACTICAL MICROSCOPY. 
 
 utmost perfection in resolution; but authorities differ on 
 this point. 
 
 For higher powers a white petal of the Pelargonium may 
 serve as a test object, it is a moderately severe test for a 
 
 FIG. 101. 
 
 FIG. 102. 
 
 J-inch ; while for higher powers still, the diatom Meridion 
 circulare will show directly whether the corrections have 
 been well executed. 
 
 Insect scales are generally used for judging the defining 
 power of higher objectives, such as the scale of the Morpho 
 Menelaus shown in Fig. 102, and that of the Podura, 
 Fig. 103. 
 
 The former exhibits lines in a longitudinal direction with 
 transverse markings, attributed to the corrugation of the 
 internal surfaces of the lining membrane, and which are 
 only to be noticed by the use of a good objective. 
 
 The Podura scale forms an excellent test of definition ; 
 it was known for this purpose before the appearance of 
 
TESTS OF DEFINITION. 
 
 Ill 
 
 Pritchard's 'Microscopic Cabinet,' published in 1832; but 
 the true character of the markings was not then known. 
 This scale was then included amongst the " line tests," 
 whilst now, with objectives of wide aperture, it presents 
 
 FIG. 103. 
 
 FIG. 104. 
 
 the appearance shown in the figure. Central light from 
 an achromatic condenser is the best for exhibiting this 
 scale, or it may be illuminated as an opaque object by 
 means of the lamp and bull's-eye condenser. 
 
 Other insect scales are to be found in use as test-objects, 
 such as those of the Lepisma saccharina shown in Fig. 104, 
 and the battledoor scales of the Polyommatus argus de- 
 lineated by Fig. 105. 
 
 These are considered much easier tests than those of the 
 M. Menelaus and Podura (Lepidocyrtus curvicollis\ but not 
 so variable in quality. Fig. 106 shows one of the ordinary 
 scales of the Morpho Menelaus, being, however, magnified to 
 but one-half the extent of Fig. 105. 
 
112 
 
 PRACTICAL MICROSCOPY. 
 
 In the use of these test objects, great attention must be 
 paid to the illumination and more particularly to the ad- 
 justment of the lenses for the thickness of the covering 
 glass. But little correction is needed with the screw collar 
 
 FIG. 105. 
 
 FIG. 106. 
 
 adjustment in the water-immersion objective, and still less, 
 if any, is required with the homogeneous system ; never- 
 theless, it should always be added, as then correction is 
 possible, should it ever be required to meet exceptional 
 cases. In the lenses made by Messrs. Ross and Co., all the 
 powers from the ^--inch upwards can be used either as 
 ''dry " or "water-immersion," by merely moving the lenses 
 by means of the adjusting collar near to the mark "wet," 
 thus avoiding the cost of extra fronts and the inconvenience 
 in changing them. Great care is required in adjusting 
 them exactly, so as to get the best performance. 
 
 3. FLATNESS OF FIELD AND FREEDOM FROM DIS- 
 TORTION. These properties in objectives may be tested 
 in several ways ; for low powers, a section of a large 
 spine of Echinus, such as shown in Fig. 107, may be used ; 
 a well cut and perfectly flat wood-section ; or perhaps 
 better still, one of Mr. Dancer's exquisite micro-photo- 
 graphs. The whole field should be well defined under 
 
SECTION OF ECHINUS SPINE. 113 
 
 one focussing, the margin as well as the centre. For 
 higher powers similar objects may be used, but of course 
 of smaller dimensions, while freedom from distortion can 
 
 FIG. 107. 
 
 be tested for, by observation of the micrometer placed upon 
 the stage, or a series of lines ruled by Wheeler, varying 
 from one thousand to ten thousand to the inch. 
 
 4. PENETRATING POWER. " Penetration," as it is 
 understood now, signifies that property which an objec- 
 tive possesses whereby several planes of an object are 
 
 I 
 
114 PRACTICAL MICROSCOPY. 
 
 brought into focus simultaneously. Until very recently 
 the property of penetration was shrouded in mystery and 
 its usefulness often exaggerated, but thanks to Professor 
 Abbe, who has made it a special study, most of the diffi- 
 culties surrounding the subject have now been cleared 
 away. 
 
 The greatest use of "penetration" is perhaps in the 
 employment of the binocular microscope, for it is only 
 when an object can be seen in its entirety that a true 
 stereoscopic image can be obtained. There is no doubt 
 also that this penetrating power is very useful for general 
 work, such as dissecting; still it should be remembered 
 that a low - angle lens with much penetration will not 
 usually stand deep eye-pieces. Dr. Blackham writes of 
 "depth of focus" as "only a residual error at best" and 
 "that it can be left in a wide-angle lens as well as in a 
 narrow-angled one." Whether this is practically correct, 
 perhaps opticians will be able to tell us, but it seems to the 
 author much more difficult to leave spherical aberrations 
 uncorrected and practically unnoticed in a wide-angle lens 
 than in one of narrow angle. 
 
 Professor Abbe has demonstrated the fact that penetra- 
 tion or " depth of vision " depends upon two circumstances : 
 first, the accommodation depth of the eye, and secondly the 
 depth of focus, varying with the quality of the images pro- 
 duced from certain distances on each side of the exact 
 focal plane. The eye, being insensible to small defects in 
 the various images, can practically discern the object in its 
 several depths, provided the images compare with sufficient 
 exactness. 
 
 The accommodation depth is very great with low ampli- 
 fications. Under a magnifying power of 10 diameters it 
 amounts to nearly 2 I millimetres, while with higher 
 powers the image passes quickly into a mere transverse 
 
PENETRATION. 
 
 115 
 
 section. The depth of focus does not diminish at such a 
 rapid rate, but the thickness of an object which can be 
 seen under one focussing decreases accordingly as the 
 amplification increases, and therefore it is most import- 
 ant, where binocular vision is essayed, to use the lowest 
 power sufficient for distinctly recognising the object ; and 
 with transmitted light to employ as narrow a pencil as will 
 sufficiently illuminate it. 
 
 The following table by Professor Abbe will sufficiently 
 illustrate these remarks : 
 
 Amplification. 
 0-50 N.A. 
 
 a. 
 
 Diameter of 
 Field. 
 
 b. 
 
 Accommoda- 
 tion Depth. 
 
 C. 
 Focal Depth. 
 
 d. 
 Depth of 
 Vision. 
 
 & + C. 
 
 Ratio a to d. 
 
 a 
 ~d 
 
 
 mm. 
 
 mm. 
 
 mm. 
 
 mm. 
 
 
 10 
 
 25-0 
 
 2'08 
 
 0-073 
 
 2'153 
 
 ii "6 to i 
 
 30 
 
 8'3 
 
 0'23 
 
 0*024 
 
 0-254 
 
 32'7 , 
 
 100 
 
 2-5 
 
 0-02 
 
 0-0073 
 
 0-0273 
 
 91-6 , 
 
 300 
 
 0-83 
 
 0-0023 
 
 O'OO24 
 
 0*0047 
 
 176*6 , 
 
 1000 
 
 0-25 
 
 0*00021 
 
 0-00073 
 
 0-00094 
 
 266 , 
 
 3000 
 
 0-083 
 
 O*OOOO2 
 
 O'OOO24 
 
 O-OOO26 
 
 3*9 , 
 
 The higher the numerical aperture of an objective the 
 less will the penetration be, though the defining and re- 
 solving power, with quantity of light admitted, increase 
 with the absolute aperture of the objective, provided the 
 aberrations are well corrected. 
 
 The following table (see next page) has been abstracted 
 from the 'Journal of the Royal Microscopical Society' 
 for August 1 88 1, wherein may also be found Professor 
 Abbe's paper from which we have largely quoted. 
 
 From the foregoing considerations, "tests" for pene- 
 tration would seem to be superfluous, seeing that it results 
 from two almost fixed conditions ; nevertheless, it is well 
 to know how it may be observed. A section of frog's lung 
 or of human liver (Fig. 108) is useful for this purpose, as 
 when mounted, the various parts will be found to have con- 
 
 I 2 
 
PRACTICAL MICROSCOPY. 
 
 NUMERICAL 
 APERTURE. 
 (n sin = a.) 
 
 Penetrating 
 Power. 
 
 (i) 
 
 Illuminating 
 Power. 
 (') 
 
 NUMERICAL 
 APERTURE. 
 (n sin u = a.} 
 
 Penetrating 
 Power. 
 
 (v) 
 
 Illuminating 
 Power. 
 (M 
 
 52 
 'SO 
 
 658 
 667 
 
 2-310 
 2*250 
 
 I'OO 
 
 0-98 
 
 000 
 020 
 
 I'OOO 
 
 0-960 
 
 48 
 
 '676 
 
 2-190 
 
 0-96 
 
 '042 
 
 0-922 
 
 46 
 
 685 
 
 2' 132 
 
 0-94 
 
 064 
 
 0-884 
 
 '44 
 
 694 
 
 2-074 
 
 0-92 
 
 OS? 
 
 0-846 
 
 42 
 
 704 
 
 2'0l6 
 
 0*90 
 
 III 
 
 0-810 
 
 40 
 
 714 
 
 960 
 
 o'88 
 
 136 
 
 0-774 
 
 38 
 
 725 
 
 904 
 
 0-86 
 
 I6 3 
 
 0-740 
 
 36 
 
 '34 
 
 746 
 
 850 
 796 
 
 0-84 
 0-82 
 
 I 9 
 '220 
 
 0-706 
 0-672 
 
 "33 
 
 752 
 
 770 
 
 0-80 
 
 250 
 
 0-640 
 
 3 2 
 
 758 
 
 742 
 
 0-78 
 
 282 
 
 0-608 
 
 30 
 
 769 
 
 6 9 
 
 0*76 
 
 316 
 
 0-578 
 
 28 
 
 7 8l 
 
 638 
 
 0-74 
 
 351 
 
 0-548 
 
 26 
 
 794 
 
 5 88 
 
 0-72 
 
 389 
 
 0-518 
 
 24 
 
 806 
 
 '538 
 
 o'7o 
 
 429 
 
 0-490 
 
 22 
 
 820 
 
 "488 
 
 0-68 
 
 471 
 
 0-462 
 
 20 
 
 833 
 
 440 
 
 o'66 
 
 'SIS 
 
 0-436 
 
 18 
 
 847 
 
 392 
 
 0-64 
 
 562 
 
 0-410 
 
 16 
 
 862 
 
 346 
 
 0-62 
 
 '613 
 
 0-384 
 
 14 
 
 877 
 
 3 00 
 
 0*60 
 
 667 
 
 0-360 
 
 '12 
 
 893 
 
 254 
 
 0-58 
 
 724 
 
 0-336 
 
 io 
 
 909 
 
 210 
 
 0*56 
 
 7 86 
 
 0-314 
 
 08 
 
 926 
 
 166 
 
 0-54 
 
 8 5 2 
 
 0-292 
 
 06 
 
 943 
 
 124 
 
 0-52 
 
 923 
 
 0-270 
 
 04 
 
 962 
 
 082 
 
 0-50 
 
 2-000 
 
 0-250 
 
 '02 
 
 980 
 
 04O 
 
 
 
 
 traded somewhat, producing corrugations or folds, and 
 consequently the rays proceed from different planes, so 
 that the test should be to see how much or how little of 
 the total depth can be seen under one focussing, without 
 indistinctness. 
 
 As an instance of the work specially suited for low 
 angles and consequent penetration, the cyclosis in Vallis- 
 neria spiralis is often cited. The author can assure his 
 readers that this may be easily seen with advantage under 
 a J-inch objective of 80 air angle (0*64 numerical aper- 
 ture), the largest yet made for this power in this country. 
 
 5. RESOLVING POWER. Without entering into any of 
 the theories of this property in objectives, it may be briefly 
 
RESOLVING POWER. 
 
 117 
 
 stated that it depends entirely upon large aperture, com- 
 bined, of course, with accuracy of the corrections for 
 sphericity and chromatism. The several pieces of appa- 
 ratus mentioned in the previous chapter are often essential 
 with objectives of wide 
 aperture, for it is ob- 
 vious that the advan- 
 tages would be lost if 
 sufficiently oblique rays 
 did not enter into the 
 formation of the image. 
 The Ross - Zentmayer 
 stand, used with a i-inch 
 or 2-inch objective as a 
 condenser, the radial 
 substage condenser of 
 Messrs. Swift and Son, 
 or the oil - immersion 
 condenser of Messrs. Powell and Lealand, are all capable 
 of producing light-rays of sufficient obliquity. 
 
 Diatom frustules, as a rule, furnish tests for the resolving 
 property of medium and high-power objectives, to which 
 may be added the insect scales already shown ; but these 
 natural tests are all of very variable quality. Gyrosigma 
 formosum and G. angulatum, shown by Figs. 109 and no 
 respectively, are tests of the resolving property of the 
 \ and |-inch objectives, both of which have been engraved 
 from photographs taken by the late Dr. Redmayne, of 
 Bolton. 
 
 Navicula rhomboides, shown in Fig. in, is used as a test 
 for the -|th objective and higher powers. It is rather a 
 difficult diatom to resolve properly without accessories, but 
 with the Powell and Lealand oil-immersion condenser it 
 may be managed without much trouble. 
 
 FIG. 1 08. 
 
n8 
 
 PRACTICAL MICROSCOPY. 
 
 Amphipleura pellucida, shown in Fig. 112, is a most 
 difficult diatom to resolve ; indeed, it cannot be accom- 
 plished by any dry objective save 
 of the widest aperture, and even 
 then it requires most careful 
 attention to the details of illu- 
 mination. 
 
 Dr. Woodward considers this 
 frustule to be the most useful 
 test for immersion objectives 
 of \ power and higher. The 
 resolution into lines is not so 
 
 FIG. 109. 
 
 FIG. no. 
 
 FIG. in. 
 
 FIG. 112. 
 
NOBERTS TEST PLATE. 
 
 119 
 
 difficult, when compared with that into dots. Mr. Wenham, 
 when describing his new illuminator for diatoms, states 
 that he was never successful in the patient manipulation 
 required to resolve this diatom by the old methods of 
 illumination. 
 
 Allusion has already been made to the variations likely 
 to occur in the markings upon the frustules of diatoms 
 and the scales of insects. In order to avoid these irregu- 
 larities, the late Herr Nobert of Pomerania issued a series 
 of test lines ruled upon glass, each band containing lines of 
 a definite number to the inch. The most popular is that 
 known as the 19-band plate, containing lines to the inch as 
 under : 
 
 
 Band. 
 
 Number of Spaces 
 per Inch, about. 
 
 Band. 
 
 Number of Spaces 
 per Inch, about. 
 
 
 
 I. 
 
 11,300 
 
 XI. 
 
 68,000 
 
 
 
 II. 
 
 17,000 
 
 XII. 
 
 73,000 
 
 
 
 III. 
 
 22,500 
 
 XIII. 
 
 79,000 
 
 
 
 IV. 
 
 28,000 
 
 XIV. 
 
 84,000 
 
 
 
 V. 
 
 34,000 
 
 XV. 
 
 90,000 
 
 
 
 VI. 
 
 39,800 
 
 XVI. 
 
 96,000 
 
 
 
 VII. 
 
 455o 
 
 XVII. 
 
 101,000 
 
 
 
 VIII. 
 
 51,200 
 
 XVIII. 
 
 106,500 
 
 
 
 IX. 
 X. 
 
 56,800 
 62,500 
 
 XIX. 
 
 112,000 
 
 
 Herr Nobert often expressed his opinion that the last 
 four bands of this plate would never be resolved by any 
 objective ; but after inspecting Dr. Woodward's photo- 
 graphs of the whole series, he produced another "plate" 
 ruled to the twentieth band, the tenth on which cor- 
 responds to the nineteenth on the old, the twentieth band 
 being ruled at the rate of 200,000 lines to the inch. 
 
 Herr Moller produces what is called a " test-platte," 
 containing 20 diatoms, mounted dry or in balsam; they 
 are arranged upon the slide in a row, at the beginning and 
 end of which is a specimen of Eupodiscus argus. The 
 
120 
 
 PRACTICAL MICROSCOPY. 
 
 following is a list of the diatoms on this " test-platte," 
 with the number of striations to the inch, as given by 
 Morley : 
 
 Diatom. 
 
 Number of Striae to the Inch. 
 
 T 
 
 Triceratium favus 
 
 
 
 
 
 2 
 
 060 
 
 to 
 
 
 080 
 
 
 
 
 
 
 
 IO 
 
 ,800 
 
 
 T' 7 
 
 
 a 
 
 
 
 
 
 
 16 
 
 -7QO 
 
 
 rS 
 
 COO 
 
 A 
 
 
 
 
 
 
 2? 
 
 ,OOO 
 
 
 07 
 
 ,000 
 
 6. 
 
 8.' 
 9- 
 
 TO 
 
 Pinnularia interrupts 
 Stauroneis Phoenicenteron 
 Grammatophora marina . . 
 Pleurosigma Balticum 
 ,, acuminatum . . 
 
 
 
 
 
 26 
 H 
 
 31 
 
 42 
 42 
 
 ,500 
 
 ,100 
 
 ,300 
 
 ,500 
 ,700 
 
 ,QOO 
 
 
 
 26 
 
 33 
 
 34 
 
 ,800 
 
 ,000 
 
 ,300 
 
 ,-200 
 
 II. 
 
 12. 
 T7. 
 
 Pleurosigma angulatum .. 
 Grammatophora subtilissima 
 Surirella gemma 
 
 
 
 
 
 43 
 61 
 
 ,800 
 ,200 
 ,4.OO 
 
 > 
 
 61 
 
 ,700 
 
 ,800 
 
 M 
 
 
 
 
 
 
 63 
 
 ,OOO 
 
 
 6T 
 
 , 300 
 
 T 5 
 
 
 
 
 
 
 -^ 
 
 , CQO 
 
 
 56 
 
 
 T6 
 
 Surirella/ gemma 
 
 
 
 
 
 67 
 
 ooo 
 
 
 ^O 
 
 ADO 
 
 17- 
 
 1 8. 
 TO 
 
 Cymatopleura elliptica 
 Navicula crassinervis 
 
 . 
 
 . 
 
 
 
 . 
 
 63 
 
 79 
 
 ,300 
 
 ,400 
 
 )> 
 
 82 
 S 1 
 
 ,200 
 
 ,7OO 
 
 20. 
 
 Amphipleura pellucida 
 
 
 
 
 
 
 
 
 
 92 
 
 ,700 
 
 
 92 
 
 ,900 
 
 It has already been mentioned that the resolving 
 power of objectives depends entirely upon their aperture, 
 with the excellence of their corrections for colour and 
 sphericity. 
 
 Objectives of low angle are generally made with posterior 
 lenses of such a size as to exclude the extreme uncorrected 
 marginal rays, or if this is not done the margins are cut off 
 by a diaphragm. The utilised portion is very fairly 
 corrected for colour, but nevertheless the spherical aberra- 
 tions, though small, must exist ; on the other hand, wide 
 apertures require large back lenses, the rays from which 
 cannot be cut off by a diaphragm without reducing the 
 angle, and therefore the corrections have to be applied to 
 the more oblique pencils ; and chromatic aberration can 
 scarcely be corrected without at the same time affecting 
 the spherical in a very great degree. 
 
IMMERSION OBJECTIVES. 121 
 
 The value of wide pencils was first put into practical 
 form by Hartnack, who made in the ordinary course of busi- 
 ness water-immersion objectives utilising pencils of light 
 approaching to 170 in air; a drop of water was placed be- 
 tween the objective and the object, and thus by passing 
 through a denser medium, rays of light entered the object- 
 glass which could not possibly enter from air, giving at the 
 same time a considerable working distance for the higher 
 powers. Some years afterwards Mr. J. W. Stephenson, 
 whose name has been already associated with the erecting 
 binocular, conceived the idea of substituting for water, in the 
 immersion objective, a fluid having the same refractive and 
 dispersive power as crown glass ; fourfold systems upon 
 this plan were calculated by Professor Abbe and made by 
 Carl Zeiss, the optician of Jena, of ^ and -|- equivalent 
 foci. These objectives had a balsam angle of 113: 
 greater than the maximum of 180 in air, in the ratio 
 of 5 to 4. 
 
 Messrs. Powell and Lealand have recently constructed a 
 homogeneous - immersion objective of T Vmch equivalent 
 focus, with a numerical aperture of I "43 or 140 balsam 
 angle, with two extra fronts, one of which gives an aperture 
 of I * 28 or 1 1 5 balsam angle, while the other provides an 
 aperture of 1*0, or 82 in balsam. With an aperture of 
 ,1*43 the working distance is 0*007 inch; the aperture of 
 I -28 gives a focal distance of 0*016 inch ; while with the 
 numerical aperture of 1*0 the working distance is 0*024 
 inch. 
 
 It was the existence of these immersion objectives and 
 their various angular values which led Professor Abbe to 
 investigate the general principles of microscopic vision. 
 He tells us that "the very first step of every understanding 
 of the microscope is to abandon the gratuitous assumption 
 of our ancestors, that microscopical vision is an imitation of 
 
122 PRACTICAL MICROSCOPY. 
 
 macroscopical, and to become familiar with the idea that it 
 is a thing sui generis, in regard to which nothing can be 
 legitimately inferred from the optical phenomena connected 
 with bodies of large size." 
 
 Professor Abbe discovered the fact that the microscopical 
 image is the result of diffraction, or the consequence of 
 those changes which are produced in rays of light by their 
 interception by minute particles ; the rays are collected at 
 the back of the objective, where they depict the direct and 
 spectral images of the source of light, reaching in their 
 further course the plane which is conjugate to the object, 
 and give rise there to an interference phenomenon, which 
 gives the ultimate image observed by the eye-piece, and, 
 therefore, the image depends essentially on the number and 
 distribution of the refracted beams which enter the objec- 
 tive.* From this it appears that the larger the number of 
 diffracted rays admitted into the objective the greater like- 
 ness to the object will the image possess, a true image being 
 only produced when all the diffracted rays from the object 
 are admitted. 
 
 Dr. G. Blackham, in a paper read before the Microscopical 
 Congress at Indianapolis, August 15, 1878, said, "Now, 
 if it is the function of the objective to collect and bring to 
 a focus rays of light too divergent to be received by 
 the unaided eye . . . the more of these lost rays that 
 a given glass can so collect and bring to a focus the 
 better the glass," and " one would naturally expect to find 
 that the improvement or evolution of the microscope was 
 accompanied by an increase of the angular aperture of the 
 objectives, and this, indeed, we find to be the case." Un- 
 
 * It is clearly beyond the scope of a work such as this to enter fully into the 
 details of this most important question. Those who wish for a more complete 
 dissertation are referred to the April number of the ' Journal of the Royal 
 Microscopical Society' for 1881, where also Professor Abbe's paper "On the 
 Estimation of Aperture " may be found.^ 
 
THE VALUE OF WIDE APERTURES. 12$ 
 
 aided, the human eye will only admit pencils of about 10, 
 and as light is dispersed from every point of an object to 
 an angle of 180, those glasses which approach infinitely 
 near this latter angle must give a more correct image of the 
 object that those of small apertures. 
 
 When we appreciate the above facts we shall be able to 
 estimate the value of immersion objectives, which enable us 
 to collect and gather to a focus rays which cannot possibly 
 enter the microscope when a film of air exists between the 
 objective and object. The editors of the 'Journal of the 
 Royal Microscopical Society ' have given diagrams of the 
 relative diameters of the utilised back lenses of dry and 
 immersion objectives of the same power, commencing with 
 an air angle of 60 and ending with the homogeneous 
 hemisphere of 1 80 balsam angle, which has nearly the same 
 refractive index as crown glass. They also add, " Thus, if 
 we commence with an air angle of 10 and proceed by 
 successive additions of 10 up to 180 air angle, passing 
 then to 82 balsam angle, and again progressing to the 
 nearest practicable approximation to 1 80 balsam angle, 
 the emergent pencils will show a continuous increase ; there 
 is no break at 180 air angle, nor does anything abnormal 
 appear at that point, but we have a regularly progressive 
 series from the lowest air angle to the highest balsam angle." 
 
 It has been urged by some, that all those rays equivalent 
 to more than 180 air angle are not image-forming rays, 
 but this assertion has also been dealt with in the same 
 journal. "The simplest experiment of all is to take a 
 homogeneous-immersion objective of large aperture, say 
 i "25 (i 10 balsam angle), and place a stop of tin-foil on the 
 back lens, leaving only a small clear annulus of the extreme 
 marginal rays. With sufficient obliquity of the illumination 
 the image of the object will be seen perfectly delineated 
 either on a bright or dark field." 
 
124 PRACTICAL MICROSCOPY. 
 
 An immense amount of discussion took place in reference 
 to these lenses in England, nearly all the opponents to the 
 system averring that by the use of an immersion fluid the 
 aperture was cut down ; that, in fact, rays which were 
 equivalent to more than 180 in air were of no practical 
 utility, even if they could be made to enter an object-glass 
 and form an image. The editors of the 'Journal of the 
 Royal Microscopical Society,' on page 305 of the ' Journal/ * 
 write : " The * aperture question ' will ever hold a most 
 prominent place in the history of the microscope, represent- 
 ing as extraordinary a series of mistakes as were ever com- 
 mitted in any branch of science, and in which (down to 
 comparatively recent times) both the leaders and the rank 
 and file were equally involved. * Aperture ' may be said to 
 have been the haschische of the microscopist ; when that has 
 formed the subject of consideration, the simplest and oldest 
 established optical principles have not been disregarded 
 merely, but their very converse tacitly assumed, as if the 
 great optical physicists of this and the previous century had 
 never lived or had written nothing that was worthy of con- 
 sideration ! " 
 
 Since penning the foregoing remarks, the author has 
 been informed by Mr. J. B. Dancer, of Manchester, that 
 for some years he has practically effected the reduction of 
 aperture in somewhat a similar manner to that indicated 
 on page 107. Instead, however, of screwing in a diaphragm 
 of definite aperture behind the back lens of the objective, 
 he uses an ingeniously constructed graduating diaphragm, 
 screwing into the lower end of the microscope body as an 
 adapter, into the lower end of which the objective is made 
 to fit. 
 
 Mr. Dancer constructed this, some years ago, to give 
 penetration to wide angle lenses, and has sent the author 
 
 * Series ii. vol. i. part 2. 
 
PROFESSOR ABBE'S NOMENCLA TURE. 1 2 5 
 
 the apparatus in question. There has scarcely been time 
 to thoroughly test the apparatus while this sheet is passing 
 through the press the author has, however, tried it upon 
 a ^-inch objective of wide aperture, and this was cut down 
 in such a manner as to enable it to be used with the 
 Wenham binocular without producing any distortion. 
 
 The working distance of the front lens was not in the 
 least altered by the contraction of the diaphragm, so that 
 the objection to most wide-aperture lenses still remains, 
 when distance from the object, either for illumination or 
 for use of dissecting instruments, is required. 
 
 Having become somewhat confused in our nomenclature 
 of apertures, on account of the unequal value of the same 
 as expressed in degrees, Professor Abbe introduced a 
 system based on his own experiments and used in harmony 
 with existing but older optical laws. Under his hand the 
 air angle of 180 was identical with the water angle of 97 
 and the balsam angle of 82, but instead of giving them 
 three separate values he introduced the term " Numerical 
 Aperture," equivalent to I o in each of the three above 
 instances. The numerical aperture is easily obtained by 
 multiplying the sine of the semi-angle by the refractive 
 index of the fluid in which that angle has been measured : 
 this is the meaning of the formula : 
 
 n sm u = a, 
 
 where n = the refractive index of the medium ; sin u = 
 the sine of the semi-angle, while a = the numerical aper- 
 ture. 
 
 A table of natural sines for each degree from i to 90 
 may be found in Chapter IX. 
 
 The following table has been printed for many months 
 upon the cover of the ' Journal of the Royal Microscopical 
 Society ' (see next page). 
 
126 
 
 PRACTICAL MICROSCOPY. 
 
 Diameters of the 
 Back Lenses of various 
 Dry and Immersion 
 Objectives of the same 
 Power (i in.) from 
 0*50 to 1*52 N. A. 
 
 NUMERICAL 
 APERTURE. 
 (n sin = a.) 
 
 Angles of Aperture (= 2 it). 
 
 Illumi- 
 nating 
 Power. 
 O 2 -) 
 
 Theoretical 
 Resolving 
 Power, in 
 Lines to an 
 Inch. 
 (A. = 0-5269 |x 
 = line E.) 
 
 Dry 
 
 Objectives 
 
 (=!.) 
 
 Water- 
 Immersion 
 Objectives 
 (= i*33) 
 
 Homo- 
 geneous 
 Immersion 
 Objectives. 
 ( = i -52.) 
 
 
 
 o / 
 
 o / 
 
 o / 
 
 
 
 
 ;52 
 
 .. 
 
 .. 
 
 180 o 
 
 2-3I 
 
 146,528 
 
 
 48 
 
 
 
 
 
 161 23 
 153 39 
 
 2-25 
 
 2-16 
 
 144,600 
 142,672 
 
 
 4 6 
 
 .. 
 
 . . 
 
 147 42 
 
 2-13 
 
 140,744 
 
 
 44 
 
 .. 
 
 .. 
 
 142 40 
 
 2-07 
 
 138,816 
 
 
 42 
 
 .. 
 
 . . 
 
 138 12 
 
 2'02 
 
 136,888 
 
 
 40 
 
 .. 
 
 .. 
 
 134 10 
 
 1-96 
 
 134,960 
 
 
 38 
 
 .. 
 
 .. 
 
 130 26 
 
 1-90 
 
 133,032 
 
 
 36 
 
 .. 
 
 .. 
 
 126 57 
 
 I-8 5 
 
 131,104 
 
 
 '34 
 
 .. 
 
 
 123 40 
 
 I -80 
 
 129, 176 
 
 
 33 
 
 . . 
 
 180* o 
 
 122 6 
 
 I'77 
 
 128,212 
 
 
 32 
 
 .. 
 
 165 56 
 
 120 33 
 
 I'74 
 
 127,248 
 
 
 30 
 
 .. 
 
 155 38 
 
 H7 34 
 
 I-6 9 
 
 125,320 
 
 
 28 
 
 .. 
 
 148 28 
 
 114 44 
 
 1-64 
 
 123,392 
 
 
 26 
 
 .. 
 
 142 39 
 
 in 59 
 
 i'59 
 
 121,464 
 
 
 24 
 
 
 
 147 36 
 
 109 20 
 
 i'54 
 
 119,536 
 
 
 22 
 
 . , 
 
 133 4 
 
 1 06 45 
 
 1-49 
 
 II7,6o8 
 
 
 '20 
 
 .. 
 
 128 55 
 
 104 15 
 
 1-44 
 
 115,680 
 
 
 18 
 
 .. 
 
 125 3 
 
 101 50 
 
 i*39 
 
 113,752 
 
 
 16 
 
 . . 
 
 121 26 
 
 99 29 
 
 i'35 
 
 111,824 
 
 
 * 14 
 
 , , 
 
 118 oo 
 
 97 ii 
 
 1-30 
 
 109,896 
 
 
 12 
 
 10 
 
 
 
 114 44 
 in 36 
 
 94 56 
 92 43 
 
 1^25 
 
 107,968 
 106,040 
 
 
 08 
 
 ,, 
 
 108 36 
 
 90 33 
 
 ri7 
 
 104,112 
 
 
 06 
 
 . . 
 
 105 42 
 
 88 26 
 
 I'I2 
 
 102,184 
 
 
 04 
 
 .. 
 
 102 53 
 
 86 21 
 
 I -08 
 
 100,256 
 
 
 O2 
 
 .. 
 
 100 10 
 
 84 18 
 
 I'O4 
 
 98,328 
 
 
 o 
 
 180 o 
 
 97 3i 
 
 82 17 
 
 I'OO 
 
 96,400 
 
 
 0-98 
 
 157 2 
 
 94 56 
 
 80 17 
 
 9 6 
 
 94,472 
 
 
 0*96 
 
 147 29 
 
 92 24 
 
 78 20 
 
 92 
 
 92,544 
 
 
 0'94 
 
 140 6 
 
 89 56 
 
 76 24 
 
 88 
 
 90,6l6 
 
 
 0'92 
 
 133 5i 
 
 87 32 
 
 74 30 
 
 85 
 
 88,688 
 
 
 0*90 
 
 128 19 
 
 85 10 
 
 72 36 
 
 81 
 
 86,760 
 
 
 O'88 
 
 123 17 
 
 82 51 
 
 70 44 
 
 '77 
 
 84,832 
 
 
 0-86 
 
 118 38 
 
 80 34 
 
 6854 
 
 ;74 
 
 82,904 
 
 
 0-84 
 
 114 17 
 
 78 20 
 
 67 6 
 
 
 80,976 
 
 
 0:82 
 
 no 10 
 
 76 8 
 
 65 18 
 
 67 
 
 79,048 
 
 
 0-80 
 
 106 16 
 
 73 58 
 
 63 3i 
 
 64 
 
 77,120 
 
 
 0-78 
 
 102 31 
 
 7i 49 
 
 61 45 
 
 61 
 
 75,192 
 
 
 0-76 
 
 9856 
 
 69 42 
 
 60 o 
 
 58 
 
 73,264 
 
 
 0-74 
 
 95 28 
 
 6736 
 
 58 16 
 
 '55 
 
 
 
 0-72 
 
 92 6 
 
 65 32 
 
 56 32 
 
 52 
 
 69,408 
 
 
 0*70 
 
 88 51 
 
 63 3i 
 
 54 50 
 
 '49 
 
 67,480 
 
 
 0-68 
 
 85 41 
 
 61 30 
 
 53 9 
 
 46 
 
 65,552 
 
 
 0-66 
 
 82 36 
 
 59 3 
 
 51 28 
 
 '44 
 
 63,624 
 
 ft 
 
 0*64 
 
 0'62 
 
 0-60 
 
 79 35 
 7638 
 73 44 
 
 57 3i 
 55 34 
 53 38 
 
 49 48 
 48 9 
 46 30 
 
 : i 
 
 61,696 
 59,768 
 57,840 
 
 v_y 
 
 0-58 
 0*56 
 
 IVl 
 
 51 42 
 49 48 
 
 44 51 
 43 14 
 
 34 
 31 
 
 55,912 
 53,984 
 
 
 '54 
 
 65 22 
 
 47 54 
 
 4i 37 
 
 29 
 
 52,056 
 
 [\~\ 
 
 0-52 
 
 62 40 
 
 46 2 
 
 40 o 
 
 27 
 
 50,128 
 
 \L/ 
 
 0-50 
 
 60 o 
 
 44 1 
 
 38 24 
 
 25 
 
 48,200 
 
CHAPTER VI. 
 
 THE COLLECTION OF OBJECTS. 
 
 IT has been the author's endeavour to persuade the student 
 to take up some special branch of study with the aid of the 
 microscope, and with this end in view the following chapter 
 has been written, showing where certain objects are to be 
 found, what apparatus is requisite for their collection, what 
 to collect, how to collect, and when gathered, how to 
 preserve them for future examination under the micro- 
 scope. 
 
 Collectors of experience will not require to be informed 
 on many of these points, and therefore to make the chapter 
 interesting to more than the mere student a list of works 
 treating on each subject has been appended, and also the 
 names of several species under each heading in order that 
 the possessor of a microscope may know what slides to 
 purchase should he desire to fill a cabinet in that manner. 
 
 The author would strongly advise the young student to 
 refrain from flitting hither and thither over the whole range 
 of microscopical objects. It is not enough to be able to 
 name a few rotifers or rare diatoms, such knowledge is of 
 the shallowest kind ; but if he sets himself to work to study 
 the life-history of some hitherto obscure organism, or the 
 anatomy of an insect, the outward form of which he is alone 
 familiar with, he may rely upon it, he will be useful in his 
 generation. 
 
 Most collectors have their own method of gathering 
 specimens, and are very conservative on this point, but the 
 
128 
 
 PRACTICAL MICROSCOPY. 
 
 telescopic walking-stick with all its fittings as shown in 
 Fig. 113, is an article generally used by all. There are 
 generally supplied with it, a ring to carry a fine muslin net, 
 a ring to hold a bottle, a weed knife, a spoon, and a drag 
 hook for weeds. 
 
 FIG. 113. 
 
 Mr. Baker, of Holborn, supplies the article in rather a 
 different form : the bottom ring is not clamped by a screw 
 as shown in the figure, but is furnished inside with a thread, 
 into which is made to screw the neck of one of the York 
 Glass Co.'s bottles. 
 
 For many purposes a pond scoop is required, such as for 
 scraping the surface of the mud at the bottom of pools 
 when searching for Oscillatoria, &c., and if it is made to 
 screw into the end of the collecting stick it will be .very 
 convenient. It is simply a ring of 
 tinned iron about 5-inches in dia- 
 meter and i -inch deep. Both edges 
 are "wired," as the tinsmiths call 
 it, so that a piece of thin muslin or 
 stout gauze may be stretched tightly 
 over it. It is shown in Fig. 114. 
 
 Some collectors prefer to secure the muslin over the 
 scoop with a firm elastic band, so that after collecting it 
 may be removed and folded up for transport home and 
 perhaps this is the better plan. 
 
 FIG. 114. 
 
THE TOW-NET. 
 
 129 
 
 The tow-net, Fig. 1 1 5, is of great use in collecting marine, 
 and even river or lake objects. It is made of fine but strong 
 muslin, tied at the large end round a wooden hoop, while 
 the nethermost extremity is secured round a small wide- 
 mouthed bottle, so that the more deli- 
 cate organisms may find their way 
 into it, and so be out of the way of 
 the currents caused by the passage 
 of the net through the water. 
 
 The tow-net, as illustrated, is fur- 
 nished with an interior net, which, 
 acting as a valve, prevents the escape 
 of organisms which have once been 
 enclosed. 
 
 Aquatic organisms, whether animal 
 or vegetable, are met with in all kinds 
 of water ; even the tap water supplied 
 by some of our corporations is ex- 
 tremely rich in specimens, while in 
 clean ponds the collector will not fail 
 to find a host of treasures ; in impure 
 streams and pools, containing sewage 
 and other decomposing matters, only 
 such common animalcula as Para- 
 mecium aurelia are to be found. 
 Other objects are fixed upon stones 
 and weeds under water, and little 
 pieces of dead stick are often found 
 covered with interesting objects. 
 
 When the water is not rich in specimens, it may be 
 necessary to concentrate them by straining off the super- 
 fluous water, which may be effected by using the filter 
 shown in Fig. 1 16. It consists of two small funnels passing 
 through a cork as shown in the figure, the one which is 
 
 K 
 
 FIG. 115. 
 
130 
 
 PRACTICAL MICROSCOPY. 
 
 inverted in the bottle being covered at the mouth with very 
 fine muslin. The water containing the organisms is poured 
 in at the top funnel, while water only issues from the stem 
 of that inverted in the water. 
 
 
 FIG. 116. 
 
 FIG. 117. 
 
 This operation may be continued until the bottle is well 
 stocked, when the contents may be carried homewards for 
 examination. 
 
 When an organism is required to be removed from a 
 
DIPPING TUBES COLLECTING CASE. 131 
 
 bottle of water, a tube or tubes of the form shown in 
 Fig. 117 will be found necessary. They may be cut from 
 ordinary glass tubing by making a cut with the edge of a 
 three-square file, and breaking it in two with the fingers. 
 The sharp edges should then be fused by holding in the 
 flame, finally allowing to cool gradually. The bent tubes 
 may be made by taking a length sufficient for two tubes 
 and softening the middle portion in the flame of an 
 ordinary gas burner or spirit lamp, and when sufficiently 
 softened the two extremities are to be pulled asunder so as 
 to form a couple of tubes of the form of B, Fig. 117, they 
 can then be cut asunder with the file and the edges fused. 
 The form A is produced in a similar manner, the softened 
 portion being drawn out obliquely. 
 
 It is a great mistake to load oneself with a host of 
 paraphernalia. The labour of carrying a heavy pack often 
 destroys what might otherwise have been an enjoyable 
 excursion. 
 
 FIG. 1 1 8. 
 
 A set of half-a-dozen small corked bottles or tubes, and 
 as many small tinned boxes, will complete the collector's 
 outfit. A small but handy pocket collecting case was 
 introduced several years ago by Stanley, of London. (See 
 Fig. 1 1 8.) 
 
 The objects having been collected, the next thing is to 
 
 K 2 
 
132 PRACTICAL MICROSCOPY. 
 
 find out what they are, genus and species, often no easy 
 task for the beginner. 
 
 One way of getting over the difficulty is by consulting 
 the books mentioned under each heading nearly always to 
 be had at the free libraries often a long, laborious, and 
 unsatisfactory task ; while the other is by sending the 
 specimens in a tube to a friend or naturalist of repute. In 
 the event of one not being known, the author has much 
 pleasure in suggesting the name of Mr. Thomas Bolton, 
 who for several years has established a naturalist's studio 
 in Birmingham.* A word to such inquirers never forget 
 to enclose a stamp for reply : many forget this, and thus 
 the willingness of the naturalist to furnish information 
 gratis becomes a serious tax upon his pocket. 
 
 We may now pass on to the enumeration of many 
 objects of interest ; but let it not be for a moment 
 supposed that it is possible to give a complete list of 
 objects suitable for microscopic study. The main wish 
 of the author is, to put before the reader something he 
 may collect easily, in the hope that he will become 
 interested in the study of the details of some one of 
 them. 
 
 ALG^E. The members of this class of Thallophytes may 
 be found almost anywhere, in ditches, streams, ponds, and 
 even in the small pools of water lying in the hoof-prints of 
 animals upon clayey or boggy soils. One of the most 
 interesting of the Algae is the Volvox globator (Fig. 119), 
 which, however, is very uncertain in its habitat. Wherever 
 found it is usually plentiful. All the fresh-water Algse may 
 be collected by the use of the appliances already mentioned. 
 Many Oscillatorise grow upon the surface of the mud at the 
 bottom of pools, and so require the scoop shown in Fig. 1 14. 
 The whole collection, including mud, should be wrapped up 
 in the muslin, and carried home in that state for examina- 
 
 * 57, Newhall Street, Birmingham. 
 
ALG^EANIMALCULA. 133 
 
 tion. The remainder of the Algae may be carried home in 
 tubes or bottles, and upon arrival should be emptied into 
 small aquaria formed of wide-mouthed bottles or small 
 propagating glasses turned upwards, the knob resting in a 
 hollow support. Whether 
 minute or not, the gatherings 
 should be examined on the 
 spot with a platyscopic lens, 
 to prevent the loading of one's 
 satchel with useless speci- 
 mens. 
 
 Marine Algae furnish many 
 beautiful objects for the 
 microscope, and can be easily 
 
 collected upon many shores. 
 
 ' FIG. 119. 
 
 Perhaps of all places, Tenby, 
 
 Torquay, and the Mumbles near Swansea are the best 
 hunting grounds. The various species of Cladophora, 
 Ptilota, Dasya, Bangia, Ceramium, and Griffithsia all form 
 good objects. 
 
 Books which may be consulted: Rabenhorst's ' Flora 
 Europaea Algarum ' ; Griffiths and Henfrey's ' Micro- 
 graphic Dictionary ' ; Johnstone and Croall's ' British Sea- 
 Weeds ' ; Hassall's ' Fresh-Water Algae/ 
 
 ANIMALCULES. Taking this term to apply to the 
 Infusoria and Rotatoria the student will find a good field 
 for study. It is scarcely possible to find a drop of water 
 which has been for any length of time exposed to the 
 air, not containing either Infusoria or Rotatoria. In some 
 waters they are found in but few numbers, while other 
 localities literally swarm with them. In the former case 
 the pond-filter shown at Fig. 116 will be found valuable. 
 The organisms may be taken from the pond or stream by 
 means of the stick and bottle, and after straining, the 
 residual water carried home in the cork tubes or bottle 
 
134 
 
 PRACTICAL MICROSCOPY. 
 
 which the collector may have with him. A word of advice 
 to the student : Do not overcrowd the organisms, and do 
 not leave any portion of the bottle or tube filled with air 
 
 if they are to be exposed to 
 shaking or concussion. On 
 arriving home the contents of 
 the tubes may be emptied into 
 small aquaria improvised from 
 broken wine glasses, or better 
 perhaps the tube can be stuck 
 through the centre of a large 
 cork and floated in a vessel 
 of water to maintain an equal 
 temperature, when the organ- 
 isms can be easily abstracted as 
 required by means of a dipping 
 tube. 
 
 Amongst the Infusoria the 
 Eiiglena viridis, Paramecium 
 aurelia, and Coleps hirtus are 
 good objects for study ; of the 
 Rotatoria, A nurcsa longispina 
 has been found in the tap water 
 furnished by the Birmingham 
 corporation, and others are to be 
 met with in the same habitat, 
 notably Triarthra longiseta and 
 Salpina redunca. 
 
 Melicerta ringens, the tube- 
 building rotifer (Fig. 120) is a 
 beautiful object, and should be carefully searched for ; it is 
 frequently found attached to water plants, such as the 
 Potamogeton crispus, or large-leaved pond-weed; the Ana- 
 charis alsinastrum and Myriophyllum spicatum. 
 
 FIG. 1 20. 
 
ARACHNIDA ANIMAL PREPARATIONS. 135 
 
 Books which may be consulted: W. Saville Kent's 'A 
 Manual of the Infusoria ' ; Griffiths and Henfrey's ' The 
 Micrographic Dictionary'; Pritchard's 'History of the 
 Infusoria.' 
 
 ARACHNIDA. This class of animal life containing the 
 spiders may become very interesting and instructive objects. 
 It seems hardly necessary to say where they may be found, 
 or how to collect them ; but it may be necessary to enjoin 
 keeping them moist when they are required for permanent 
 objects or for dissection ; diluted glycerine or diluted acetic 
 acid will effect this. 
 
 The respiratory system, the circulating system, the spin- 
 ning organs, and even the eggs, are very interesting, but a, 
 knowledge of dissection must be gained before the student 
 can make a successful study of this branch. 
 
 The Arachnida are very plentifully distributed the mites 
 or Acarini, such as the Acarus domesticus (cheese mite) and 
 the Acarus farince (flour mite) are good objects for the 
 J-inch objectives used binocularly, either alive or when 
 mounted without pressure. 
 
 Books which may be consulted: ' Micrographic Dictionary ' ; 
 Blackwall's ' British Spiders ' (Ray Society) ; Walker's 
 ' British Spiders ' (Ray Society). 
 
 ANIMAL PREPARATIONS. The number of these objects 
 is legion ; and little else can be done here than to say that 
 animal preparations, as a rule, require special preparation 
 and treatment. Still there is the raw material to collect, 
 and this should be carefully preserved, in order that when 
 examined, its characters shall be faithfully delineated. 
 
 The hairs of animals and scales of fish present no unusual 
 difficulties; but such subjects as skin, tongue, liver, lung, 
 &c., should be reserved until the student has become a 
 moderately expert experimentalist. Frogs, mice, rats, rab- 
 bits, and guinea-pigs are generally pressed into this service. 
 
136 
 
 PRACTICAL MICROSCOPY. 
 
 Books which may be consulted : 'How to Work with the 
 Microscope/ Beale ; Brunton, Foster, Klein, and Sander- 
 son's ' Handbook for the Physiological Laboratory ' ; Syl- 
 vester Marsh's ' Section Cutting ' ; Rutherford's ' Practical 
 Histology.' 
 
 CRUSTACEA. In this branch are specimens innumerable, 
 the Entomostraca being included under this head. They 
 may all be taken with the appliances already mentioned, 
 and what will do for Infusoria will also be sufficient for 
 Crustacea. Daphnia pulex, the water flea ; Cyclops quadri- 
 cornis ; Cypris tristriata ; A rgulus foliaceus, the fish louse ; 
 Asellus vulgaris, the water wood-louse ; Gammarus pulex, 
 the fresh- water shrimp; Bosmina longirostris (Fig. 121); 
 
 FIG. 121. 
 
 Chirocephalus diaphanus, the fairy shrimp, are all to be 
 found in easily accessible ponds during the spring, summer, 
 and autumn. 
 
 Books which may be consulted: Baird's 'British Entomo- 
 straca' ; 'The Micrographic Dictionary.' 
 
DIATOMACE&. 137 
 
 DlATOMACE^E. This probably has been the most attrac- 
 tive class to nearly all microscopists. Diatoms are a family 
 of Confervoid Algae, in which the protoplasm is enclosed in 
 silicious valves, generally covered with very fine markings, 
 the nature of which has not yet been satisfactorily made 
 out. They are found in fresh, brackish, and salt water, 
 adhering to plants and stones, or scattered amongst peat, 
 water mosses, or Oscillatoriae, and even upon damp ground. 
 Nothing is easier than their collection, but of course it is 
 not always possible to meet with the specimens desired. 
 
 Diatoms are often found in the stomachs of fish, especially 
 crustaceans and molluscs, and several species have been 
 found in the internal arrangements of Noctiluca miliaris, a 
 small exceedingly transparent organism of the size of a 
 grain of mustard seed, causing a phosphorescence in the 
 sea. 
 
 A little experience will enable any one to find and to 
 gather all he may desire. Those living in the city can 
 easily procure many beautiful varieties by simply fastening 
 a muslin bag like an umbrella cover to the hydrant. After 
 securing a quantity of the sediment, empty it into a large 
 fruit jar or other receptacle nearly filled with water, and let 
 it settle. 
 
 The green, brown, or fawn-coloured scum on the surface 
 of pools, bogs, and marshes, is mostly diatoms, and it may 
 be taken up by means of a spoon or bottle and preserved, 
 always in alcohol and water, or dried upon paper. The 
 living weeds should be taken carefully from their location 
 without much compressing or washing. The finer water 
 plants yield the richest harvest. Fresh-water forms are 
 sometimes found hanging in green-coloured masses from 
 drains, sluices, and water-pipes. To gather from the lake, 
 a net of fine muslin, having an opening in the bottom in 
 which a wide-mouthed phial is tied, may be towed at the 
 
138 
 
 PRACTICAL MICROSCOPY. 
 
 stern of a steamer. The sediment left in the bottom of 
 pails, barrels, and other vessels contains a good supply. To 
 obtain varieties not found at home, open a correspon- 
 dence with gatherers in other localities, who will gladly 
 exchange. 
 
 Dr. Redmayne, in a short communication to 'Science- 
 Gossip' in 1875, described the simple arrangement for 
 diatom collection shown in Fig. 122. 
 
 FIG. 122. 
 
 A cork must be provided which fits the collecting bottle 
 tightly ; this is to be bored with two holes : in each is fitted 
 a glass tube as shown in the figure, one having a slight 
 curve a, the other b bent at right angles an inch from 
 the end. To the tube b is attached a piece of indiarubber 
 tubing about the length of the collecting-stick, and the free 
 end c may be held in the hand or fastened to the stick 
 with a small elastic band. 
 
 To use the apparatus, the thumb of the right-hand must 
 
DR. REDMAYN&S APPARATUS. 
 
 139 
 
 press the tube firmly against the stick at c and the bottle be 
 lowered until the mouth of the tube is within a quarter of 
 an inch of the diatoms ; the thumb is then to be raised, and 
 if the water is deep the bottle will fill by atmospheric pres- 
 sure, carrying in the diatoms at the same time. In shallow 
 water suction will be necessary to exhaust the air in the 
 bottle, in which case the bulb pipette shown at B in the 
 same figure will be useful as a mouthpiece. 
 
 In the collection and recognition of 
 diatoms, the student will find Professor 
 Brown's pocket microscope a useful ad- 
 junct, as it is furnished with a deep 
 eye-piece and objectives of an inch, and 
 a fifth of an inch focus. It is shown in 
 Fig. 123. 
 
 Great care should be taken in the 
 collection of diatoms, so as to have them 
 in as pure a state as possible, as it is 
 not easy to separate them from foreign 
 matter when it is mixed up with them. 
 The late Dr. Redmayne placed the 
 gathering in a long bottle in the sun for 
 a few hours, the lower half of the bottle 
 being covered with black paper. The 
 free diatoms separate themselves from 
 the mud and come to the surface, and 
 can thus be removed. 
 
 Fossil Diatomaceae also exist in im- 
 mense quantities in various places. The large deposits of 
 guano, the Bermuda deposits, the Berg-mehl in Norway, 
 the Mourne Mountain deposit in Ireland, the recent dis- 
 covery of diatoms in the London clay by Mr. Shrubsole, 
 and the still more recent discovery in Llyn Arenig Bach, 
 about midway between Bala and Festiniog, in North Wales, 
 
 FIG. 123. 
 
PRACTICAL MICROSCOPY. 
 
 show that the Diatomaceae are, and have been, very widely 
 distributed. 
 
 Some collectors may consider the pocket microscope 
 shown in Fig. 123 not steady enough for general use, and 
 therefore may prefer the form shown in Fig. 124 as made 
 
 FIG. 124. 
 
 by Mr. Browning and others ; it is exceedingly portable 
 and very steady, as the author can testify from its practical 
 use when travelling in North Wales. 
 
 Amongst the diatoms which may be singled out for 
 examination are Pleurosigma angulatum (Fig. no), P. 
 formosum (Fig. 109), Navicula firma (Fig. 125), N. lyra 
 (Fig. 126), N. rhomboides (Fig. in), Isthmia enervis, 
 Arachnoidiscus Ekrenbergii, Meridian circular e y Diatoma 
 vulgare, and a host of others. 
 
 Whilst writing this chapter the author has received a 
 tube of diatoms from Mr. Bolton of Birmingham, consist- 
 ing of a number of species found attached to algae in the 
 canal of that neighbourhood ; the most easily recognised 
 
DIA TOMSECHINODERMA TA. 
 
 141 
 
 were: Bacillaria paradoxa, Nitzschia sigmoidea, N. lanceo- 
 lata, Grammatophora marina, A mphiprora alata, Pinnularia 
 radios a, and P. viridis. 
 
 FIG. 125. 
 
 FIG. 126. 
 
 Books which may be consulted: Rabenhorst's 'Flora 
 Europaea Algarum ' ; J. Smith's ' British Diatomaceae ' ; 
 Donkin's ' British Diatomaceae ' ; and Schmidt's ' Diato- 
 macean Atlas.' 
 
 ECHINODERMATA. The marine objects, star- fishes, sea- 
 eggs, or sea hedgehogs, may always be taken at- low water 
 after a spring tide. In their earlier stages they are ex- 
 tremely interesting, being infusoria-like organisms, and 
 often appearing without any internal structure whatever. 
 They furnish the microscopist with abundance of material. 
 The prickles or spines, hooks, and the pedicellaria make 
 interesting and instructive objects. 
 
 A section of Echinus spine is used as a test for the 
 flatness of field in low-power objectives, while a section of 
 a small spine may be used for the same purpose with higher 
 
142 PRACTICAL MICROSCOPY. 
 
 powers. A section of one of these may be seen delineated 
 in Fig. 107. 
 
 Books which may be consulted: Forbes's ' British Star- 
 Fishes ' ; Agassiz's ' Echinodermata Viv. et Foss.' 
 
 FERNS require no special apparatus for collecting save a 
 sharp knife and a tin collecting box ; they form a very 
 interesting study. The stem may be double stained, as 
 described in the chapter on the staining and injecting of 
 objects. 
 
 How many microscopists are there who possess fern 
 preparations in their cabinet, spores and sori, stems in 
 cross and vertical section, double and single stained, and 
 yet are totally unacquainted with the life-cycle of a single 
 species ; who have looked at sori and spores innumerable, 
 and yet never made the effort of allowing these to ger- 
 minate, and to observe them in their various and strange 
 mutations. 
 
 The Lastrea filix-mas, or male fern, is one of the best 
 species to study for the beginner, and there are many 
 others easily found, such as A thyrium filix-fcemina (lady 
 fern), Scolopendrium vulgare (hart's tongue), Pteris aqui- 
 lina (common bracken),- A diantum capilhis- Veneris (maiden 
 hair), and many others. 
 
 Books which may be consulted : Moore's ' Index Filicum ' ; 
 'Handbook of British Ferns' ; Newman's ' British Ferns ' ; 
 J. Smith's ' Ferns, British and Foreign ' ; Hooker and 
 Baker's ' Synopsis Filicum.' 
 
 FORAMINIFERA. These gelatinous, structureless ani- 
 mals are mostly sought after for the sake of the shells, 
 serving them as a covering. The shells are pierced with 
 holes, through which the animal protrudes its pseudopodia, 
 using them as a means of locomotion. They are found 
 in largest numbers in the sand and mud from the sea- 
 bottom, but may also be found on sea-weeds, and in 
 
FORA MINI PER A . 
 
 the fossil state in chalk, limestone, and other mineral 
 deposits. From sea-soundings they may be procured by 
 dissolving out the tallow in which they are collected, by 
 means of benzine any sort of benzine or benzoline serving 
 this purpose. To obtain fossil Foraminifera from chalk, 
 the pieces must be broken up small by means of a hammer, 
 and then gently crushed in an iron mortar. The powder is 
 then to be placed in a piece of coarse calico, tied up like a 
 pudding, and put into a large basin of water, and well 
 kneaded, until reduced to one-third its original bulk. The 
 milky fluid is then to be poured off, until only one-fourth 
 remains, and the operation of washing, by stirring up with 
 
 FIG. 127. 
 
 fresh water, and allowing to settle, repeated many times, 
 until a portion of the residue, on examination under the 
 microscope, shows that most, or all, of the extraneous 
 matter has been eliminated. 
 
144 PRACTICAL MICROSCOPY. 
 
 The illustration Fig. 127 shows a section of chalk from 
 Gravesend with Foraminifera in situ. 
 
 Amongst others, Lagena squamosa, Orbitolites compla- 
 natus, Polystomella crispa, and Nodosaria raphanus, are 
 very good objects. 
 
 Books which may be consulted: Williamson's ' Recent 
 Foraminifera ' (Ray Society) ; Carpenter's ' Introduction 
 to the Study of Foraminifera.' 
 
 FUNGI. Micro-fungi may be found everywhere, and 
 make a splendid study. Many of them, however, can only 
 be examined successfully when in the fresh state, such as 
 Penicillium crustaceum and Aspergillus glaucus, the common 
 moulds and mildews of our houses. Nearly every plant 
 and tree is attacked at one time or another by some parti- 
 cular species of micro-fungus, so that the student will find 
 plenty of work in this class alone. We have the Puccinia 
 graminis upon the leaves and stems of standing corn, as 
 well as Tilletia caries and Ustilago segetum or smut, which 
 fill up and destroy the whole contents of the ear ; the 
 JEcidium on the berberry bush ; Triphragmium on the 
 leaves of the meadow-sweet ; the blackberry brand, Aregma 
 bulbosum; Coleosporium synantherarum on the colt's-foot ; 
 Cystopus candidus on cabbages ; Peronospora infestans on 
 our potatoes ; Peronospora gangliformis on lettuces ; and 
 Peronospora vici<z on peas : a host of others being within 
 easy reach. 
 
 The micro-fungi shown in Fig. 128, are as follow: 
 
 a. Stachybotrys lobulata. 
 
 b. S. atra. 
 
 c. Penicillium sitophilum (Oidium aurantiacutn). 
 
 d. Myxotrichum deflexum. 
 
 e. Polyactis fascicularis, 
 
 f. Sporocybe alternata (Aspergillus alternate). 
 
 g. Rhopalomyces pallidus. 
 
 h, Papulaspora sepedonioides. 
 i. Acremonium alter natum. 
 
MICRO-FUNGIINFUSORIA . 
 
 They have all been found upon moist cotton goods or in 
 analogous situations. 
 
 All that is necessary in collecting micro-fungi is to well 
 isolate each specimen, preferably by wrapping in soft paper, 
 and placing separately in a small box. 
 
 FIG. 128. 
 
 Books which may be consulted: 'Outlines of British 
 Fungology/ by Rev. M. J. Berkeley, F.R.S. ; ' Handbook of 
 British Fungi/ by M. C. Cooke ; ' Rust, Smut, Mildew, and 
 Mould/ by M. C. Cooke; 'Selectae Fungorum Carpologia/ 
 3 vols., Tulasne. 
 
 INFUSORIA AND ROTATORIA. Nearly all that is neces- 
 sary to say under this head has been given when treating 
 of animalcules. Fresh-water infusoria may be collected in 
 wide-mouthed bottles, and the individuals selected for 
 examination removed by means of one of the dipping tubes 
 shown in Fig. 117. The members of this class of animals 
 are generally to be found attached to weeds. The beautiful 
 
 L 
 
146 
 
 PRACTICAL MICROSCOPY. 
 
 Stephanocerus Eichhornii is one of this class ; it is shown in 
 
 Fig. 129. The author has before him at the present 
 
 moment some leaflets of Myriophyllum spicatum, the 
 
 common water -weed, completely 
 covered with Melicerta ringens, Flos- 
 cularia cornuta, Philodina megalo- 
 trocha, Limnias ceratophylli, Eu- 
 chlanis dilata, and Codosiga botrytis. 
 Most of these organisms may 
 be obtained from Mr. Bolton's 
 studio. 
 
 Books which may be consulted (see 
 Animalcules). 
 
 INSECTS afford an inexhaustible 
 series of treasures to the micro- 
 scopist; but in order to examine 
 these perfectly, a knowledge of dis- 
 section must be gained. The head, 
 eyes, legs, wings, proboscis, spiracles, 
 and tracheae, all make instructive 
 objects. Many are the kinds of 
 insects that can be pressed into the 
 microscopist's service, the Siphonop- 
 tera, or fleas; the Parasitica, or 
 lice ; the Diptera, or flies ; the 
 Hymenoptera, bees and wasps ; 
 Lepidoptera, butterflies and moths ; 
 Orthoptera, grasshoppers and cric- 
 kets ; the Coleoptera, or beetles, are 
 
 all too well known to require instructions when, how, and 
 
 where to collect. 
 
 Fig. 130 shows the male Dytiscus marginalis, or great 
 
 water beetle, a very interesting insect to the microscopist, 
 
 while Fig. 131 is a picture of the female. 
 
 FIG. 129. 
 
INSECT A. 
 
 The larvae too are an interesting study ; this stage in the 
 gnat, dayfly, and even of the Dytiscus, Fig. 132, will amply 
 repay the observer for the attention he bestows upon it. 
 
 FIG. 130. FIG. 131. 
 
 When required for immediate examination, no special 
 care is requisite; but if for dissection and permanent 
 mounting afterwards, they should 
 be immersed in a mixture of 
 equal parts of glycerine and 
 water, dilute acetic acid, or even 
 dilute alcohol (for some things 
 which require hardening), in 
 order to ensure preservation. It 
 must be understood, however, 
 that this is not universally ap- 
 plicable. There are some objects 
 which would be spoiled by im- 
 mersion in a fluid, and these, of 
 course, must be prepared while 
 in the fresh state. FlG - I32< 
 
 The scales of several insects are much used as test objects, 
 notably those of the Lepisma saccharina, Morpho menelaus, 
 
 L 2 
 
148 PRACTICAL MICROSCOPY. 
 
 the Polyommatus argus, the Lepidocyrtus curvicollis, and 
 Podura plumbea. These scales are shown in Chapter V. 
 The Podura plumbea is a small insect found in damp shady 
 
 places, under stones in 
 cellars, where they may 
 be caught by sprinkling 
 a little oatmeal near 
 their haunts. They are 
 
 F commonly called spring- 
 
 tails ; and in order to 
 
 help the student in finding them, an illustration is given 
 in Fig. 133, and of the Lepisma saccharina in Fig. 134, each 
 magnified about 12 diameters. 
 
 FIG. 134. 
 
 It is very interesting at times to watch the development 
 of insects and the changes they undergo during their cycle 
 of existence ; for this purpose a " vivarium " is necessary, so 
 that while furnishing them with sufficient air they may be 
 prevented from crawling or flying away, and the respired 
 carbonic acid find easy exit. 
 
 The best kind of vivarium is that shown in Fig. 135, and 
 is so simple that an ordinary tinman can construct one for 
 a trifling cost. 
 
 The framework is made of perforated zinc with a bottom 
 of the same material, on which rests an inner circle of zinc but 
 perforated more closely. This is not fastened to the bottom 
 
VIVARIUMLICHENS. 
 
 149 
 
 but can be raised at will ; it is covered with a round piece of 
 flat glass. On this stands a saucer of well moistened clay 
 stuck round the edge 
 with such leaves as the 
 insects feed on. In the 
 centre of this saucer is a 
 small vase rilled daily 
 with fresh flowers and 
 grasses for the butter- 
 flies. 
 
 It is easy in this ap- 
 paratus to raise moths, 
 butterflies, and other 
 winged insects, such as 
 saw-flies and the like, 
 from the egg; and the 
 many changes may be 
 watched through the 
 glass, from the emerg- 
 ence of the caterpillar 
 from the egg to the exit 
 of the imago from the 
 pupa case. 
 
 LICHENS. These in- 
 teresting vegetable pro- 
 ductions require but an 
 old knife and a few pill- 
 boxes for their collec- 
 tion, with occasionally a hammer and chisel. The purer 
 the atmosphere of the district the greater variety to be 
 found, while in a smoky and gas - polluted atmosphere 
 they are either not found at all, or only to be met with 
 in the gonidial state, when they may be easily mistaken 
 for protophytal algae. Lichens are to be found growing 
 
 FIG. 135. 
 
150 
 
 PRACTICAL MICROSCOPY. 
 
 upon rocks, stones, trees, old railings, twigs, bushes, heath, 
 moss, and in many other places. 
 
 Lichens are mostly of large size, and require thin sections 
 to be cut ere the structures can be satisfactorily made out ; 
 but some should be always mounted as opaque objects, to 
 show what the natural form of the plant is. 
 
 FIG. 136. 
 
 FIG. 137. 
 
 Fig. 1 36 shows a piece of fencing upon which is growing 
 Lecanora cerina, while the next illustration, Fig. 137, shows 
 Usnea barbata, one of the filamentous species. Among 
 the more familiar kinds are Parmelia parietina, Lecidea 
 
MINERALS. 
 
 canescens, Physcia ciliaris, Cladonia pyxidata, and Pertu- 
 saria communis. 
 
 Books which may be consulted: 'History of British 
 Lichens/ W. L. Lindsay, M.D. ; ' Lichenes Britannici,' 
 Crombie ; ' The Lichen Flora of Great Britain and Ireland/ 
 Rev. W. A. Leighton. 
 
 MINERALS. Of late years much has been discovered in 
 the mineral kingdom by the aid of the microscope, but 
 owing to the nature of the substances to be examined, 
 much preparatory work has to be done ere a satisfactory 
 examination can be made. Sections have to be cut and 
 semi-polished ere the structure can be well made out, and 
 this will be described in our next chapter. Barbadoes rock 
 showing Polycistina in situ, oolitic and nummulitic lime- 
 stone, slags from iron and copper furnaces, fossil wood, 
 
 FIG. 138. 
 
 minerals used in smelting, basalt, boiler incrustations, coal, 
 shale, lava, and many other minerals, furnish instructive 
 objects, and may be collected in plenty in the proper 
 localities. 
 
 A section of porphyrine is shown in Fig. 138, which 
 
152 
 
 PRACTICAL MICROSCOPY. 
 
 forms an illustration of the production of crystalline forms 
 
 when molten vitreous matter is allowed to cool slowly. 
 
 This mineral is of a beautiful crimson colour, and under a 
 
 binocular microscope few objects 
 can vie with it for beauty. 
 
 The two figures, 139 and 140, 
 show the artificial production of 
 similar crystals during the manu- 
 facture of glass. When the 
 " metal " is cooled slowly, crys- 
 tals of certain forms are obtained, 
 which vary in form according to 
 the differences existing in the 
 quantities of the materials from 
 which the glass is made. 
 Books which may be consulted: 'Sur les Crystallites/ 
 
 Vogelsang ; Allport on the " Microscopical Examination 
 
 FIG. 140. 
 
 of Rocks and Minerals," p. 98, 'Monthly Microscopical 
 Journal' ; 'Mineralogy and Study of the Rocks/ Rutley. 
 MOLLUSCS. The entire series of the Mollusca form very 
 
MOLLUSC A. 153 
 
 interesting objects for the microscope, the structure of the 
 viscera, the spermatozoa, and the tongue or odontophore 
 being the chief. Fresh-water and land snails should be 
 avoided by the student until he has gained sufficient 
 experience in the manipulation of limpets and whelks, from 
 which the extraction of the odontophore is a comparatively 
 easy operation. The marine molluscs may be carried long 
 distances folded in damp sea-weed, while fresh-water snails 
 should be conveyed in a similar manner in damp Anacharis. 
 When the animals are not immediately required, they may 
 be dropped into glycerine, dilute acetic acid, or into alcohol. 
 Edwards advises that they be dropped into caustic potash 
 solution (say one part of caustic potash and two of water), 
 until they begin to decompose ; but of course this is only 
 admissible when nothing but the odontophore is required. 
 
 This odontophore is the so-called tongue or lingual 
 ribbon, really the masticatory apparatus, a long ribbon-like 
 organ furnished with a com- 
 plicated system of teeth, gene- 
 rally set upon flattened plates. 
 The form and arrangement of 
 the teeth furnish characters 
 of much importance in classi- 
 fication, and therefore should 
 be studied by all those who 
 are interested in this depart- F IG . I4I . 
 
 ment of natural history. 
 
 Fig. 141 shows a short length of the odontophore of the 
 common limpet, Patella vulgata. 
 
 Books which may be consulted. ' British Mollusca/ 
 Forbes and Hanley ; " Notes on Victorian Molluscs and 
 their Palates," C. M. Mapleston, 'Monthly Microscopical 
 Journal/ vol. viii. p. 45 ; Alcock, ' Proceedings of Man- 
 chester Literary and Philosophical Society.' 
 
154 PRACTICAL MICROSCOPY. 
 
 MOSSES. These require but few instructions for collect- 
 ing. They are of little use for the purposes of scientific 
 inquiry without fruit, and therefore the collector should 
 always endeavour to procure the plant in fructification. 
 Polytrichum commune, Sphagnum squarrosum, Hypnum 
 purum, Tortula (Barbula) muralis, are amongst the more 
 common species. 
 
 Every month produces some species to be collected ; on 
 old walls, the roofs of tiled and thatched buildings, on our 
 garden walks, on our downs and commons, on chalk and 
 sandstone, in bogs and on the mountain-top, mosses may 
 be found everywhere. The necessary apparatus for col- 
 lecting consists of an old pocket-knife, a platyscopic lens, 
 as shown in Fig. 2, a satchel or small bag, and a good 
 supply of thin envelopes, or square pieces of tissue or 
 other thin paper, in which to wrap each species. 
 
 Books which may be consulted. Hooker, Taylor, and 
 Wilson's ' Bryologia Britannica ' ; R. Braithwaite's ' British 
 Moss Flora ' ; Stark's ' Popular History of British Mosses ' ; 
 Berkeley's ' Handbook of all British Mosses ' ; Unwin's 
 ' Dissections and Illustrations of British Mosses/ 
 
 POLYCISTINA. These animals are a family of Rhizo- 
 poda Radiolaria, the silicious skeletons of which form a 
 series of very interesting objects for the microscope. They 
 exist on every ocean floor and embedded in rocks, fossil 
 Polycistina having been found at Oran, Bermuda, and 
 Barbadoes, as well as in many other places. The silicious 
 skeletons, or shells, as they are sometimes termed, with 
 their prolongations, are aids in discriminating between 
 Polycistina and Foraminifera, which former some of the 
 species resemble. A section of Barbadoes rock, showing 
 Polycistina in situ, is often a pretty, interesting, and in- 
 structive object. These objects may be obtained from 
 Barbadoes earth, by boiling with its own weight of washing 
 
POL YCISTINAPOL YZOA. 1 5 5 
 
 soda and a similar weight of water for one hour. After 
 allowing to settle, the " flock " must be poured off and the 
 boiling with soda repeated, with intermediate washing 
 several times. Rhopalocanium ornatitm, Podocyrtis Schom- 
 burghii, and Astromma Aristotelis are, perhaps, the most 
 beautiful of this class. 
 
 Books which may be consiilted : Haeckel's ' Die Radio- 
 larien ' ; ' The Micrographic Dictionary.' 
 
 POLYZOA. These interesting objects have, by the 
 researches of modern inquirers, become much more known ; 
 they are both marine and fresh-water, and may be found in 
 many rivers and canals. 
 
 On the sea-shore they are very plentiful, forming a crust 
 on submerged rocks, or attached to stones, shells, and sea- 
 weed. The individual animal is termed zpolypide, and the 
 colony a ccencecittm, which latter consists of an aggregation 
 of cells or cups, often taking elegant and vegetable forms. 
 Most Polyzoa are fixed organisms, but one at least the 
 Cristatella mucedo is capable of locomotion. 
 
 One beautiful form, the Lophopus crystallinus, may be 
 found constantly in the Gorton Canal, near Manchester, 
 and is much sought after by microscopists, visitors to the 
 neighbourhood ; it is shown in Fig. 142. 
 
 The study of these animals is an interesting one. In 
 L. crystallinus, as shown in the figure, a is the region of the 
 mouth ; , the oesophagus ; c y the stomach ; d, the intestine ; 
 e are the retractory muscles ; /, a statoblast ; h, the mouth ; 
 i, tentacles retracted, partly within cell ; k, the outer trans- 
 parent envelope ; /, the perigastric space ; m, the lopho- 
 phore ; and at n the tentacles have been excised, to show 
 mouth. 
 
 Of marine Polyzoa, the sea-mat, or Flustra foliacea, may 
 be taken as a type ; it is most plant-like and flexible. The 
 cells are narrow at the base and rounded at the end, with 
 
156 PRACTICAL MICROSCOPY. 
 
 scattered marginal spines ; when rubbed betwixt the fingers 
 it exhales an odour resembling oil of lemon. An illus- 
 tration of this common object of the sea-shore is given at 
 
 FIG. 142. 
 
 Fig. 143, while in the next figure (144) is shown a portion, 
 much enlarged. 
 
 When collected, they must be preserved in bottles or 
 
POLYZOA VEGETABLE PREPARATIONS. 1 57 
 
 tubes with some of the water they were taken from, while 
 it has been stated that they may be preserved with 
 expanded tentacles by dropping alcohol into the water; 
 but this is not always successful. 
 
 FIG. 143. 
 
 FIG. 144. 
 
 Books which may be consulted: W. Saville Kent's 
 * Manual of the Infusoria'; Johnstone's ' British Zoo- 
 phytes ' ; ' Micrographic Dictionary ' ; Allman, ' Fresh-water 
 Polyzoa' (Ray Society). 
 
 VEGETABLE PREPARATIONS. The raw material for this 
 branch of study may be found everywhere, the vegetable 
 kingdom being able, perhaps, to supply more objects for 
 the microscope than all the other classes together. Algae, 
 diatoms, ferns, fungi, lichens, and mosses, have already 
 been mentioned, but the phanerogams alone are able to 
 furnish matter for an immense amount of observation. The 
 
PRACTICAL MICROSCOPY. 
 
 stems of trees and shrubs, the pine, fir, hornbeam, box, 
 birch, beech, oak, chestnut, and elder, being easily ac- 
 cessible, are interesting when cut into sections. The leaves, 
 seed, pollen, roots, hairs, cuticles, raphides, and a host of 
 other preparations, may be obtained from almost any plant, 
 whether it be a choice specimen from the greenhouse or a 
 common weed from the garden. 
 
 The starches form a study in themselves, and are specially 
 interesting from many points of view ; they are easily pre- 
 pared and should be kept dry, in small homoeopathic tubes, 
 for observation. The grains, such as wheat and barley, 
 may be bruised and set aside for a few days to ferment, 
 when, upon squeezing through a fine cotton cloth, the 
 milky liquid contains the starch. Roots, rhizomes, and 
 tubers require to be rasped, and the milky fluid 
 strained in the same manner. After a time, the starch 
 granules subside, when the supernatant fluid must be 
 poured off and fresh water added, the whole stirred up, 
 and allowed to settle again. After pouring off the water, 
 the granules should be allowed to drain upon blotting- 
 paper and dried at the temperature of the air in a warm 
 room. Fig. 145 shows several of the commoner forms of 
 starch. 
 
 Nothing special is required for the collection of raw 
 material for vegetable preparations, without it be a tin 
 case, for holding leaves, stems, or the whole plant, and 
 squares of soft tissue paper, in which to carefully fold 
 specimens. In collecting pollen, it is well to gather the 
 complete flower, and carefully isolate the specimens in 
 order that no confusion of the granules may take place. 
 The pollen of a species of the mallow tribe is often used 
 as a test object for low-power objectives. It is shown in 
 
 Fig- 97- 
 
 Works which may be consulted : Ma6t and Decaisne's 
 

 FIG. 145. 
 
i6o 
 
 PRACTICAL MICROSCOPY. 
 
 ' Descriptive and Analytical Botany/ by J. D. Hooker ; 
 Sachs' 'Text-Book of Botany' (Clarendon Press); Balfour's 
 ' Manual of Botany/ 
 
 ZOOPHYTES. This division includes the Hydrozoa and 
 the Actinozoa, both of which furnish many objects for 
 study. In the first class we find the Hydra viridis and 
 H. fusca, which may be collected without much trouble 
 from streams and pools; it is visible to the unassisted eye, 
 though it can only be satisfactorily examined by the aid 
 of the microscope. Fig. 146 shows H. viridis as it usually 
 occurs attached to duckweed, and in the same manner it 
 is often found on Anacharis alsinastrum and other water 
 plants. 
 
 FIG. 146. 
 
 Another order of the Hydroid Zoophytes is the Tubu- 
 larida, of which Tubularia ramea is a specimen. It is com- 
 monly called the "branched pipe coralline," and is a 
 marine organism ; in fact, all the Tubularida are marine 
 with the single exception of the genus Cordylophora, which 
 inhabits fresh water. The Tubularia ramea may be seen 
 in Fig. 147. 
 
 Amongst the Actinozoa are the sea-anemones, the coral 
 polypes, and the Cydippe (Pleurobrachia pileus). 
 
ZOOPHYTES. 161 
 
 The life-history of the zoophytes is extremely interesting, 
 and the student will scarcely be able to appreciate that the 
 ovoid ciliated mass, seen escaping from the ova of the parent, 
 would ever lose its cilia and develop into the parental 
 form. 
 
 FIG. 147. 
 
 When it is desired to keep them for preservation and 
 mounting, the same method may be employed as for 
 Polyzoa, to drop alcohol into the water in which they have 
 been collected, which is stated to kill them while causing 
 but little retraction of the tentacles. 
 
 Books which may be consulted: 'The Micrographic Dic- 
 tionary'; Johnstone's 'British Zoophytes'; Hincks' 'British 
 Hydroid Zoophytes/ 
 
 M 
 
CHAPTER VII. 
 MICRO-DISSECTIONS. 
 
 MANY of the objects mentioned in the preceding chapters 
 cannot be examined under the microscope without sub- 
 division or previous preparation, either on account of their 
 size, or because the parts lie iri different planes, the trans- 
 parent portions being hidden from view by others of an 
 opaque character. 
 
 This is so with most insect life, especially the larger 
 species, though, on the other hand, the more minute kinds, 
 such as the Acarus domesticus, or cheese-mite, are generally 
 so transparent as to require no special treatment. 
 
 Beetles and other insects, flies, snails, frogs, and newts 
 are very good examples of the former class, and the student 
 will do well to practise the dissection of these objects. He 
 will find it absolutely necessary to acquire a good know- 
 ledge of dissection, in order to gain a correct insight into 
 the relative structure of the insect economy. 
 
 We can hardly describe in words how to proceed in each 
 individual case. Experience will come by practice, and 
 the student will find that each subject becomes more and 
 more easy, especially if, before commencing in haste with 
 the needles and scissors, he will study the general arrange- 
 ment of organs in his subject, by reference to some one or 
 other of the many standard works in existence, obtainable 
 at any free library. 
 
 One remark, however, is necessary. Do not hurry on 
 with imperfect dissections of a host of subjects ; stick to 
 
SIMPLE DISSECTING MICROSCOPES. 
 
 163 
 
 one insect until a good knowledge of its anatomy has been 
 gained, and by no means take the trouble to prepare and 
 mount any imperfect specimens. Persevere until the dis- 
 sections are perfect, and then spare no trouble or pains in 
 preserving them for future reference. 
 
 Dissections may be carried on with but few instruments ; 
 a few small-sized troughs, 
 knives, scissors, needles, and 
 camel-hair pencils are nearly 
 all the requisites. The dis- 
 secting microscope must be 
 left to the taste of the ope- 
 rator, who will find many 
 forms to select from. 
 
 Fig. 148 shows Collins' 
 cheap dissecting microscope, IG * * 4 
 
 of which a large number are in use in Professor Henslow's 
 botanical classes ; while the next figure (149) is an illustra- 
 
 FIG. 149. 
 
 tion of Houston's botanical dissecting microscope, which 
 may suit botanists who wish for nothing more than a steady 
 stand for a pocket magnifier. 
 
 This ingenious little instrument is intended to provide 
 working botanical students with a convenient and service- 
 able dissecting microscope at a moderate cost. The box 
 measures, when closed, 9 inches long, 4 inches wide, and 
 
 M 2 
 
1 64 
 
 PRACTICAL MICROSCOPY. 
 
 2 inches deep, and is so constructed that, by using a divided 
 sliding lid (acting as a support for the dissecting stage), a 
 rest for the wrists is secured while the hands are employed 
 in dissecting. 
 
 The duplex lens, giving three powers, 4, 6, and 10 dia- 
 meters, is screwed to the end of a brass focussing tube 
 moving upon a brass pillar attached to a sliding bar at the 
 bottom of the box. The lens may at any time be un- 
 screwed and carried in the pocket. 
 
 FIG. 150. 
 
 The dissecting stage is a cork slide, plain on one side for 
 general work, but provided with a shallow cell on the other, 
 for the dissection of such objects as small glossy seeds, which 
 " fly " under the needles. A pitted glass slide, to be used 
 when the object is best dissected under water, is also pro- 
 vided. A cutting needle, two dissecting needles, and a 
 pair of small forceps are also included, and the whole is 
 sold at the moderate price of 6s. 6d. 
 
 Fig. 1 50 is a representation of Lawson's dissecting micro- 
 scope as made by Mr. Collins a very handy and compact 
 instrument, containing, as it does, in the unfolded case the 
 knives, needles, and scissors for the operator's immediate use. 
 
BINOCULAR DISSECTING MICROSCOPE. 
 
 I6 5 
 
 Recognising the advantages of binocular vision for the 
 purposes of dissection, as well as the erection of the image, 
 Mr. Baker and also Messrs. Swift and Son have introduced 
 a cheap form of the Stephenson binocular, as shown in 
 Fig. 151, the details of which have already been described 
 on page 35. 
 
 FIG. 151. 
 
 If the erection of the image be desired, it can be obtained 
 by the use of the draw-tube and erector already illustrated 
 by Figs. 32 and 33, and this method has many advantages 
 over the use of the Stephenson binocular. The erector 
 screws into the end of the draw-tube, and using the A eye- 
 piece with a J-inch objective any amplification from 2-5 to 
 66 diameters may be obtained, or from 12 to 260 diameters 
 
i66 
 
 PRACTICAL MICROSCOPY. 
 
 with the D ocular. It must not be forgotten, however, that 
 the use of the erector disturbs the corrections of the objec- 
 tive, producing spherical and chromatic aberrations. This 
 is so great that, when using the A eye-piece and a i-inch 
 objective, an object may be brought to an indifferent focus 
 at any distance between i inch and 2^ inches from the front 
 lens upon the instrument shown in Fig. 24 ; but at \\ inches 
 perhaps the sharpest image is formed. The way to remedy 
 the effect of these aberrations is to use the C or D eye- 
 pieces, when the object runs in and out of focus very 
 sharply, and as the peripheral rays are not gathered in, 
 there is but little aberration of either kind visible. 
 
 The following table will show the use of the erector and 
 draw-tube, used upon the stand in Fig. 24 with a -inch 
 objective of 50 air angle. 
 
 
 A Eye-piece. 
 
 D Eye-piece. 
 
 Position of 
 Draw-tube. 
 
 Distance 
 of Front 
 Lens from 
 Object. 
 
 Size of 
 Object in 
 Field. 
 
 Amplifi- 
 cation in 
 Diameters. 
 
 Distance 
 of Front 
 Lens from 
 Object. 
 
 Size of 
 Object in 
 Field. 
 
 Amplifi- 
 cation in 
 Diameters. 
 
 
 in. 
 
 in. 
 
 
 in. 
 
 in. 
 
 
 Full home 
 
 1*30 
 
 0'75 
 
 2'5 
 
 I'05 
 
 0*40 
 
 12*0 
 
 Withdrawn \ inch 
 
 0-60 
 
 o'40 
 
 7'0 
 
 0-44 
 
 OT5 
 
 30-0 
 
 1 
 
 0-36 
 
 O'2O 
 
 II'O 
 
 0'36 
 
 0*09 
 
 50-0 
 
 * 
 
 0-23 
 
 0'12 
 
 20'0 
 
 0-23 
 
 0'05 
 
 QO'O 
 
 ^ ;, 
 
 0-17 
 
 0*06 
 
 40-0 
 
 0-17 
 
 0'03 
 
 iSo'O 
 
 3 
 
 0-15 
 
 0*04 
 
 60-0 
 
 0-IS 
 
 0'02 
 
 260 'o 
 
 For cheapness, there is nothing better than the watch- 
 maker's or engraver's eye-glasses. These may be fixed 
 into any form of stand the ingenuity of the student may 
 devise, and with these alone very much work can be done, 
 quite as much perhaps as he will be able to execute for 
 some time. 
 
 The subjects for dissection are usually operated upon 
 under water or some other fluid, in dilute alcohol, or even in 
 glycerine. This is a very convenient medium in which to 
 
DISSECTING TROUGHS. 167 
 
 carry on minute dissections, as the operation can be per- 
 formed with much more certainty than is the case in more 
 mobile fluids. 
 
 In whatever fluid the specimen for dissection be im- 
 mersed, a trough is necessary to hold it, such as shown 
 in Fig. 152, and this may be either of guttapercha or 
 glass, not too large, but roomy enough for working, and 
 also for the disposal of loose matter. Half an inch in 
 depth is ample (except for special subjects), as if deeper, 
 the sides are apt to interfere with the free use of the 
 needles and fingers. 
 
 If the trough is of glass, a suitable bedding may be run 
 in to a depth of a 
 quarter of an inch, to 
 which the subject can 
 be pinned down. A 
 translucent bottom 
 may be made of a 
 mixture of napthalin 
 
 and stearine, an FIG ^ 
 
 opaque bedding of 
 
 equal parts of resin and beeswax, thinned to the neces- 
 sary consistency with unsalted lard, and coloured black 
 with lamp-black, or white with oxide of zinc or dried 
 china-clay. 
 
 While dissecting, no instruments are more handy than 
 ordinary sewing needles, thrust with the eye first into 
 cedar-wood handles. They may be bent to any required 
 shape while heated in the gas or a spirit-lamp flame, 
 and afterwards rehardened by heating and. plunging, while 
 hot, into oil. They must be kept well polished, as if any 
 roughness prevail on their surface it is next to impossible 
 to produce anything but torn and disfigured dissections. 
 
 Camel-hair pencils are indispensable agents for the 
 
i68 
 
 PRACTICAL MICROSCOPY. 
 
 removal of loose matter, torn and unrequired portions of 
 the insect anatomy, and also for the arrangement of the 
 dissected portions. 
 
 The knives used in dissecting should be of good steel, 
 and kept in order by the occasional application of a 
 Washita oilstone. Some of the most useful forms are 
 shown in Fig. 153 two or three will perhaps be selected ; 
 the author prefers the forms shown at a, b, d, f and h. 
 
 Nearly every microscopist prefers to work his own way, 
 and with his own choice of instruments. The spear-head 
 needles sold by Mr. Ward of Manchester will be found 
 exceedingly useful. 
 
 Three kinds of scissors are generally required by the dis- 
 sector, the curved, Fig. 1 54, elbow, Fig. 155, and plain, Fig. 
 156. They must be well made, and kept carefully cleaned 
 and free from rust. The application of mercury ointment 
 
SCISSORS SPRING SCISSORS. 
 
 169 
 
 will usually go far in protecting steel instruments from this 
 enemy. 
 
 Another pair of scissors is also much used in minute dis- 
 sections, one leg of which is fixed in a light ebonite handle, 
 
 FIG. 154. FIG. 155. 
 
 FIG. 156. 
 
 the blades being kept apart by means of a spring. The 
 pressure of the finger on the loose leg causes the blades to 
 close, and it will be found after a little practice that the 
 instrument may have many applications. It is shown in 
 Fig. 157. 
 
 FIG. 157. 
 
 The steel forceps, shown in Fig. 158, are necessary 
 adjuncts to the dissector, and he should be careful to 
 select those of but medium strength in the spring, and 
 such as can be depended upon for seizing an object 
 finely yet firmly, and not at all liable to twist aside and 
 spoil the subject under dissection. A pair of curved 
 
I/O PRACTICAL MICROSCOPY. 
 
 forceps, as well as a pair of the straight variety, with fine 
 points, are necessary. 
 
 A bull's-eye condenser for concentrating light upon the 
 object, and a small glass syringe for washing subjects and 
 removing or adding to the liquid contents of the trough, 
 complete the dissector's outfit. 
 
 And now having his apparatus ready, the student will 
 naturally be looking about for something to dissect. He 
 need not seek long at any season of the year, but in the 
 
 FlG - 
 
 event of his not being able to fix on what he shall com- 
 mence with, the blow-fly, Musca vomitoria, is suggested. 
 
 Plenty of work will be found in the blow-fly if it be done 
 properly, and after this the student may take in hand 
 the water-beetle, Dytiscus marginalis ; the grasshopper, 
 Locus fa mridissima ; or the common house cricket, Acheta 
 domestica. 
 
 In the above, the student will find the tongues, antennae, 
 eyes, wings, legs, segments, spiracles, and tracheae, an 
 interesting study, and besides these organs, gizzards will 
 be found in the last three. 
 
 rftie insect (if not too large) should first be held in the 
 stage forceps as shown in Fig. 66, or in any other con- 
 venient manner, and examined with a low power (say a 
 2-inch objective), to show its general character, and give an 
 insight into the manner in which the appendages should be 
 dealt with. 
 
 The proboscis of the fly may be obtained by pressing 
 the thorax, so as to cause protrusion, placing the organ 
 
DISSECTING THE BLOW-FLY. 17 1 
 
 upon a strip of glass, covering with a thin square cover, 
 and severing with a sharp knife. If the insect has been 
 killed with chloroform, the organ will generally be found 
 protruding. Just a word en passant to encourage the 
 student to display his dissections naturally, in order to 
 give observers an idea of the real use of the various organs 
 in the insect economy. This cannot be better illustrated 
 than by reference to this proboscis, one of the late Mr. 
 Topping's favourite preparations. The more natural con- 
 dition should be mounted in glycerine, and though not so 
 pretty an object, is at least truthful. 
 
 Put no insect to pain. Kill it at as early a stage in the 
 inquiry as is possible, either with chloroform, bruised laurel 
 leaves, or by means of the cyanide of potassium bottle now 
 so often used. 
 
 Proceeding with the blow-fly, the wings may be detached 
 from the thorax by means of the knife, scissors, or forceps, 
 the legs taken off at the thigh, the halteres or poisers 
 detached, and the antennae cut from the head, completing 
 the list of appendages. The carcase must now be pinned 
 down in the trough, or fixed to the bedding by warm- 
 ing a spot with a hot iron, fixing the subject into the 
 melted stratum, and the integument carefully slit up with 
 a fine pair of scissors, upon both sides. The chitinous 
 skeleton must then be raised with the forceps, and the 
 attachments cleared away with the aid of a blunt needle 
 and a spear-headed instrument, when, if tolerably well per- 
 formed, the whole of the organs will be seen in situ. The 
 subject should now be left in a mixture of glycerine and 
 water (equal parts of each), for about twelve hours, after 
 which treatment the organs may be readily dissected. Dilute 
 alcohol is very useful when dissecting the nervous system 
 of insects. A more or less prolonged immersion hardens 
 the nerve fibre, which the student will find requires very 
 
172 
 
 PRACTICAL MICROSCOPY. 
 
 delicate handling. It is not difficult to find and take away 
 the tracheal system (though the beginner will find this 
 easier to prepare from the silk-worm or caterpillar), and 
 the muscles which are used for raising and depressing the 
 wings during flight may be found without much trouble. 
 
 FIG. 159. 
 
 FIG. 160. 
 
 The digestive apparatus varies somewhat in different 
 insects, and as an aid to the student the arrangement of 
 these organs is given as they appear in situ in the water- 
 beetle (Fig. 159) and the blow-fly (Fig. 160). 
 
 The fly lives by suction, and therefore the food does not 
 require any unusual amount of mastication. It therefore 
 
DISSECTIONS. 173 
 
 has no gizzard. The water-beetle, on the other hand, has 
 a gizzard placed at the end of the oesophagus or gullet, its 
 object being to more completely triturate the food before it 
 passes into the stomach. The gizzard is composed of hard 
 muscular tissue, and nearly always covered internally with 
 hard growths called teeth. 
 
 In Fig. 1 59, A is the oesophagus or gullet, B the gizzard, 
 D the stomach, E the small intestine, while the large oval- 
 shaped sac at the extreme left is the large intestine. 
 
 If the gizzard only is required, the best plan is (after 
 killing) to hold the insect under water, and with the forceps 
 to draw the head from the body. Most of the internal 
 organs will by this means be drawn out, when the gizzard 
 can be detached with the scissors from its place below the 
 gullet, washed, and opened out with knife and needle. 
 
 After having proceeded so far, the student will do well to 
 examine the nervous system, and last of all, when the inside 
 has been cleared out, the segments and spiracles may follow 
 in their turn. 
 
 Insects intended for dissection should never be allowed 
 to become dry, and if they cannot be treated at once they 
 should be preserved in dilute glycerine, dilute acetic acid, 
 or weak spirit, according to what is required of them after- 
 wards. 
 
 The student perhaps may not have patience at first 
 to go through the whole set of dissections from one 
 insect, and, therefore, such objects as the saws of the 
 different saw-flies may be attractive. Several different 
 varieties are shown in Fig. 161. 
 
 The variation in the form of saw from the different 
 species, as illustrated in figure, has been carefully studied 
 and the drawings made by Mr. J. W. Gooch. No. I is the 
 saw of the large green saw-fly ; 2, the black saw-fly ; 3, 
 small black saw-fly ; 4, a brownish saw-fly ; 5, black saw- 
 
174 
 
 PRACTICAL MICROSCOPY. 
 
 fly, with white-banded abdomen ; 6, large yellow saw-fly ; 
 7, yellow saw-fly with black thorax. 
 
 The saw-flies are common everywhere, especially in the 
 neighbourhood of gooseberry bushes ; the saws are really a 
 part of the ovipository arrangement, and are attached of 
 course to the abdomen of the females. 
 
 FIG. 161. 
 
 The sting and poison-bag of the bee is not difficult to 
 obtain (that of the humble-bee is shown in Fig. 162), 
 though the student will find perhaps that it requires deli- 
 cate manipulation to separate the long tubular gland from 
 the tracheae ; this may, however, be done with very smooth 
 
5 TINGING A PPA RAT US OF HUMBLE-BEE. 1 7 5 
 
 needles under an amplification of about 10 diameters in 
 water and using a small camel's-hair pencil to brush away 
 loose matter. 
 
 FIG. 162. 
 
 The wasp may also be pressed into the service of the 
 dissector, and here he will find some remarkable differences 
 over the bee ; the poison-bag is separated from the body of 
 
PRACTICAL MICROSCOPY. 
 
 the sting by a long tube, and the bag itself is so well covered 
 with muscular fibres that it is impossible to separate them 
 
 FIG. 163. 
 
LARVA OF CRANE-FLY. 
 
 177 
 
 from it without tearing the whole to pieces. The sting, 
 lancet, and poison-bag of wasp may be seen in Fig. 163. 
 
 The object of dissecting, after all, is not to be able to 
 prepare pretty slides merely, 
 but to gain a knowledge of the 
 anatomy of our subject, so 
 that we may understand more 
 thoroughly the various trans- 
 formations which take place. It 
 may not be possible always to 
 isolate each organ we wish, and 
 in that case a careful study 
 should be made of the organs 
 in situ sometimes by polarised 
 light, and what we have actually 
 seen may be transferred to paper 
 by any of the methods described 
 in the chapter on " the Delinea- 
 tion of Objects." 
 
 An instance of this may be 
 found in Fig. 164, where the 
 internal organisation of the larva 
 of the crane-fly is delineated. 
 To lay out the various organs as 
 there shown would be a task of 
 supreme difficulty ; but a draw- 
 ing may be made of them from 
 the student's observations. 
 
 Another study having an in- 
 terest with many is that of the 
 tongues, palates, lingual ribbons, 
 or odontophores, of molluscs. FlG ' l64 ' 
 
 The subjects for dissection should be killed by drop- 
 ping them into glycerine, and so preserved until they are 
 
 N 
 
PRACTICAL MICROSCOPY. 
 
 required. The dissection should be carried on under 
 water, in the usual way, though the mollusc needs but little 
 pinning down. 
 
 Let the student start with the common periwinkle, 
 Littorina littoralis, or, perhaps better still, with Patella 
 vulgata, or common limpet. In the former, the lingual 
 ribbon will be found coiled up like a watch-spring by open- 
 ing the back of the animal, and this place will be found 
 generally the best of all to examine first. 
 
 In Patella vulgata it is only necessary to remove the 
 
 foot, or broad flat 
 disc forming the lower 
 surface of the body, 
 when the lingual rib- 
 bon is exposed to 
 view, and appears as 
 shown in Fig. 165. 
 
 The Trochus zizi- 
 pkinus, or pearly-top, 
 may also form a sub- 
 ject, as it is found in 
 tolerable profusion on 
 our shores ; and the 
 whelk, Buccinum un~ 
 datum, will also fur- 
 nish new specimens. 
 
 In T.ziziphinus,\he 
 floor of the mouth 
 
 must be exposed from above, when the lingual ribbon will 
 be found lying upon it. In the whelk, the trunk contains 
 the whole of the ribbon, and may be seen by opening the 
 back just behind the tentacles. 
 
 In Fig. 1 66 the periwinkle is well displayed : / is the 
 foot, m the muscle for withdrawing the animal into his 
 
 FIG. 
 
DISSECTION OF VEGETABLE MATTER. 
 
 179 
 
 shell, g the spittle glands, th the throat, s the stomach, r the 
 
 odontophore, br the breathing gills, a anus, and o the ovary 
 
 carrying eggs. 
 
 The next illustration shows an oyster lying in its shell 
 
 (Fig. 167) ; m is the lower half of the mantle, wt a piece of 
 
 upper half, g the breathing gills, 
 h the heart, Iv the liver, Ip the 
 lips, o the opening of the mouth, 
 a the anus, ms muscle holding 
 shells together, and c elastic 
 cushion keeping shells apart. 
 
 FIG. 166. 
 
 Dissection of vegetable matter is usually preceded by pro- 
 longed immersion in water, in order to soften the parts to 
 be separated ; but very often indeed the tissues withstand 
 this action, and so recourse is had to various other solu- 
 tions which are found necessary. Caustic soda in dilute 
 solution is a favourite reagent for the differentiation of 
 vegetable matter. It is the solution used by the paper- 
 maker for the disintegration of the leaf of esparto grass, 
 the fibres of which furnish him with a valuable paper-making 
 material. 
 
 Fibro-cellular tissue may be conveniently studied in the 
 
 N 2 
 
180 PRACTICAL MICROSCOPY. 
 
 leaves of orchids, where it is easily found, underneath the 
 cuticle, after maceration. Woody tissue, often the chief 
 component of certain plants used in the arts, is composed 
 of fibro-vascular vessels aggregated in bundles, as in flax 
 for instance ; and the same may be said of jute, china- 
 grass, and many other products. These fibres may be 
 examined by macerating in water, during which a fermen- 
 tation sets in, and the fibrous bundles consequently split 
 up ; the same effect may be produced by boiling with 
 dilute caustic soda solution. 
 
 Spiral fibres also form interesting objects for study. 
 They occur sometimes in cells alone, and at others in con- 
 junction with what have been styled bordered pores, as in 
 the yew and araucaria, while the pores are found alone in 
 the pine. Most woods, when in thin shavings, are easily 
 decomposed by boiling with dilute nitric acid, when the 
 fibres can be pulled asunder, or by boiling with caustic 
 soda solution under pressure. 
 
 Spiral vessels are even more interesting than any of the 
 foregoing, and easily procured. From the stem of the leek 
 they are separated with ease, while from the petiole of the 
 common garden rhubarb they can be obtained in plenty by 
 searching in a pot of this preserve. 
 
 Perhaps of all exercises the complete dissection of a moss 
 is the best for botanical students ; the various parts 
 mounted on an ordinary slip under a three-quarter thin 
 glass cover are at once a type slide and an object of 
 beauty. 
 
 Scalariform vessels are to be met with in the roots of 
 ferns. The Pteris aquilina perhaps displays them as well 
 as any other plant ; but it is a moot point whether they are 
 better seen by the examination of a dissected portion, 
 rather than a section made in a diagonal direction. It is 
 true that much can be made out from sections of the 
 
THE VALUE OF DISSECTIONS. l8l 
 
 various parts under study ; but without dissection we 
 should be very apt to arrive at erroneous conclusions con- 
 cerning the form and situation of parts, our views often 
 being modified by the light thrown upon our subject by its 
 employment. 
 
CHAPTER VIII. 
 SECTION-CUTTING. 
 
 IN the preceding chapter the necessity of dissection has 
 been shown, in order to gain an insight into the economy 
 of things. It is none the less important, however, to be 
 able to cut a thin slice of any given object in order to show 
 the details in situ. 
 
 We should be very careful not to form hasty opinions, 
 from the observation of sections alone, as vessels will 
 appear of different shapes according to the plane in which 
 they have been cut. Circular vessels cut through obliquely 
 give an oval outline ; but in the direction of their length, 
 squares. 
 
 Section-cutting may conveniently be divided into three 
 methods : 
 
 1. Without the use of the microtome (section-cutter), and 
 even before hardening or otherwise preparing the subject. 
 
 2. With the microtome, such subjects as the stems of 
 plants, leaves, animal preparations, and the like. 
 
 3. The cutting of hard substances, coal, rock, bone, and 
 subjects of this nature. 
 
 To proceed with the first method, we find some workers 
 cutting slices on or between pieces of cork without the use 
 of any appliance whatever save a knife or razor. Others 
 use even more primitive methods, and perhaps by long 
 continued practice may arrive at fair results, though the 
 author has never seen uniformly thin and good specimens 
 cut by the hand alone. 
 
 Some when examining animal tissues, " prefer to snip off 
 
VALENTIN'S KNIVES. 
 
 183 
 
 a piece with a pair of sharp scissors," or " cut a piece off 
 with a sharp scalpel," but all slides prepared in this manner 
 are mere fragments compared with the splendid sections of 
 Marsh, Cole, Wheeler, Norman, Ward, and others. 
 
 FIG. 168. 
 
 Fresh animal tissues, such as kidney or liver, are 
 frequently cut with Valentin's knife (Figs. 168 and 169). 
 
 FIG. 169. 
 
 This instrument is formed of two narrow blades lying 
 parallel to each other, their distance being regulated by 
 means of a fine screw. The knife is used immersed in 
 water ; it is drawn through the tissue to be cut, in a saw- 
 like fashion, the sections being afterwards disengaged by 
 shaking the blades gently in water. Dr. Maddox's form of 
 this knife is one with triple blades, so that a double section 
 might be cut, to show opposite but contiguous surfaces. It 
 is shown in Fig. 170. 
 
 FIG. 170. 
 
 Dr. Sylvester Marsh, who has written a small manualette 
 upon the subject of section-cutting, has devised a simple 
 but useful spoon for lifting thin sections. It is shown in 
 Fig. 171. 
 
 After all, these methods of cutting are exceedingly 
 
1 84 
 
 PRACTICAL MICROSCOPY. 
 
 limited in their application. They may be necessary at 
 times, when it is desired to make a hurried examination ; 
 
 but the student is certainly 
 advised never to make 
 hurried examinations. 
 
 We now come to the 
 second division, where sec- 
 tions are cut in the micro- 
 tome, of which there are 
 several forms, constructed in 
 accordance with the require- 
 ments of the originators. 
 The most common form of section-cutter is shown in 
 Fig. 172. It is generally used for cutting sections of wood, 
 stems, and other semi-hard substances. The substance to 
 
 FIG. 171. 
 
 FIG. 172. 
 
 FIG. 173. 
 
 be cut is kept firmly in position by means of the side screw, 
 and the quantity necessary for each section sent up by the 
 screw below. 
 
 Another section-cutting machine used for the same 
 
RUTHERFORD'S MICROTOME. 
 
 purpose as the preceding has been devised by Mr. Hailes, 
 and is sold by Messrs. Baker, of Holborn. All the faults 
 of the old form have been remedied, and for cutting semi- 
 hard substances it is the best of its kind (Fig. 173). 
 
 The microtome which the real worker in sections should 
 procure, is that of Professor Rutherford, inasmuch as it has 
 special uses in itself, and can also be made to do whatever 
 
 FIG. 174. 
 
 has been done with any other machine. It can be used 
 with a cereous bedding or as a freezing microtome at will. 
 The woodcut Fig. 174 shows the instrument. 
 
 Mr. Dancer, of Manchester, makes a good microtome for 
 use with a cereous bedding. The well is large and square, 
 
1 86 
 
 PRACTICAL MICROSCOPY. 
 
 the plug of considerable length, moved upwards by means 
 of a good firm screw, while the cutting plate is of steel. 
 If this microtome were so arranged that it could be used in 
 a freezing mixture, the writer would not hesitate to place 
 it in the first rank, and even before that of Professor 
 Rutherford. The well being square the subject cannot 
 revolve, and no "rise" takes place when the correct bedding 
 agent is employed. 
 
 A form of microtome designed by Mr. Williams and 
 made by Messrs. Swift and Son, is shown in Fig. 175. It 
 
 FIG. 175. 
 
 is specially designed for use in the freezing process, and 
 has been admirably described in the Journal of the Quekett 
 Club. Not having used it the author can but give his 
 opinion that the principle upon which it is constructed is 
 good, though there seems to be very little superiority over 
 Professor Rutherford's. 
 
RAZOR-GUARDS. 187 
 
 The student having become' furnished with a microtome, 
 his next selection must be a knife or razor, and in his 
 choice he must remember that it is absolutely necessary 
 for the whole of the back and edge to lie in the same plane 
 both must slide together over the top plate with perfect 
 smoothness of motion. The knife or razor should be 
 hollow-ground, flat-ground knives and razors being re- 
 served for cutting wood or bone, where great strength is 
 required. The cutting instruments must be kept to a very 
 keen edge by use of a Washita oil-stone, combined with 
 the application of a good razor-strop. It requires practice 
 to put on the keenest edge. Perhaps a lesson from a 
 barber would on the whole be a cheaper and speedier way 
 of learning. 
 
 Mr. M. H. Stiles has described an arrangement by which 
 the blade of the razor is kept from contact with the plate 
 of the machine, by two small screw-clamps he terms " razor- 
 guards " (Fig. 176). These slide on the blade, one being 
 fixed at each end, and kept in position 
 by a small screw in the upper side of 
 each. They are f ths of an inch wide 
 and are made from sheet brass ^th of FlG " I7<5 ' 
 
 an inch thick. They ensure a smoother and more steady 
 motion than by cutting in the old way, and the edge of the 
 razor is preserved in much better condition as it touches 
 nothing but the substance to be cut. 
 
 Let us now consider the cutting operation. If we wish 
 to cut a section of the stem of the horse-chestnut (sEscufas 
 hippocastanum), Fig. 98, say in a line with the axis of 
 growth, we shall find it rather difficult, without first 
 embedding in some agent to hold it firmly, and without 
 undue pressure upon any one part. Formerly a mixture 
 of equal parts of beeswax and olive oil was used for this 
 purpose, and Professor Rutherford advises a mixture of 
 
1 88 PRACTICAL MICROSCOPY. 
 
 five parts of paraffin with one part of hog's lard. Both of 
 these mixtures are liable to become loose in the cylinder, 
 often rotating during the cutting operation, and also 
 " rising," and thereby spoiling the work by uneven 
 thickness. 
 
 Mr. John Barrow has improved this bedding by making 
 a mixture of naphthalin and stearine in certain proportions, 
 which vary according to the temperature of the air and 
 its consequent behaviour under the knife. It can be mixed 
 in quantity and kept in a large glue-pot, or even a stone- 
 ware jar or preserve-pot, and remelted by standing in hot 
 water when required for use. 
 
 This mixture does not become loose in the well of the 
 microtome like the paraffin mixture, and never " rises," so 
 that sections are easily cut of a uniform thickness. 
 
 Having soaked the stem in water, in order to soften it 
 somewhat, it should be dried externally and dipped into 
 the following solution, which has been carefully filtered : 
 
 Finest gum-arabic . . . . 60 grains. 
 
 Glycerine 5 drops. 
 
 Alcohol I o drops. 
 
 Water 2 ounces. 
 
 The stem must then be withdrawn and allowed to drain 
 upon blotting-paper until surface dry, when it is held in 
 the fluid bedding agent in the well of the microtome, until 
 the naphthalin mixture has become hard, the plug having 
 been previously depressed, by means of the screw, to the 
 depth required. 
 
 When quite cold the cutting may be commenced, and 
 the first cut or two made with an ordinary razor and dis- 
 carded, being only intended to level down and to ascertain 
 if all be right. After levelling, the second cut with the 
 section razor should be examined under a low power, and 
 if it is not thin enough more care must be taken with the 
 
CUTTING VEGETABLE SECTIONS. 189 
 
 subsequent cuttings. After every cut, the necessary thick- 
 ness must be sent up by means of the screw below, 
 and if the cutting has been done properly, i. e. by a firm 
 diagonal push from point to handle of the knife, keeping 
 this also back and edge at the same time upon the cutting 
 plate, the section will finally look like the illustration in 
 Fig. 98. 
 
 During the cutting operation the knife or razor should 
 be kept flooded with dilute glycerine or weak alcohol, and 
 the section may be easily liberated from the knife by 
 gently shaking in a basin of water. The glycerine and 
 gum surrounding the sections dissolves after a few minutes, 
 allowing them to fall to the bottom, while the naphthalin 
 mixture floats on the surface of the water. 
 
 Most vegetable substances can be cut in this way, leaves 
 and stems among the rest ; but some will require prepara- 
 tion before inserting into the microtome. Those which are 
 too hard must be soaked in water until soft enough to cut, 
 or even immersed in boiling water if necessary. Excess of 
 water may be abstracted by soaking in alcohol (methylated 
 spirit) for a time, or by partial desiccation. Whenever it 
 is required to eliminate resinous substances methylated 
 spirit will perform the operation, but it must not be for- 
 gotten that alcohol extracts the colouring matters from 
 most vegetable substances. 
 
 Very good sections of certain woods can be made with 
 an ordinary smoothing plane, such as is used by joiners. 
 Deal may be cut in very thin ribands by this means, and 
 when mounted dry, constitutes Dr. Carpenter's test for the 
 colour correction of objectives. 
 
 A word of. advice to the beginner may here be neces- 
 sary : discard all sections not showing the leading features 
 intended ; they are worthless from a scientific point of 
 view, yet it is strange how many there are in existence. 
 
PRACTICAL MICROSCOPY. 
 
 Fig. 177 is an illustration of a section of a lichen thallus, 
 and Fig. 178 a similar slice from the apothecium: mounted 
 sections should show the details as well as these. 
 
 FIG. 177. 
 
 FIG. 178. 
 
 Animal tissues require different treatment. They are 
 generally too soft and pulpy for immediate cutting, so 
 require to be soaked for various periods in some hardening 
 solution ; while others, such as porcupine-quill, whalebone, 
 and horn, require immersing in hot water to soften them. 
 
 For hardening animal tissues, alcohol, and chromic acid 
 solution are most generally used, while some prefer bi- 
 chromate of potash, or bichloride of mercury. Alcohol is 
 perhaps the safest of all hardening agents ; it being a 
 powerful abstractor of water, coagulating albumen, and 
 acting also as a preservative agent. 
 
 Chromic acid is to be obtained in beautiful dry carmine 
 crystals. It is more conveniently kept as a stock solution, 
 I ounce being dissolved in 50 ounces of water, and diluted 
 as occasion requires. 
 
 It must not be forgotten that tissues are easily over- 
 hardened and rendered brittle by prolonged immersion in 
 chromic acid, and therefore the weaker a solution can be 
 used the better. Some tissues require hardening by special 
 
HARDENING ANIMAL TISSUES. 191 
 
 means. Rutherford advises brain to be soaked in the 
 following solution : 
 
 Chromic acid 15 grains. 
 
 Bichromate of potash 31 grains. 
 
 Water 43 ounces. 
 
 Small pieces are first immersed for twenty-four hours in 
 methylated spirit, drained on blotting-paper, and then 
 soaked for five or six weeks in a large quantity of the 
 above solution, changing it several times in that period. 
 Adipose tissue may be hardened in methylated spirit ; 
 liver prepared for cutting by soaking in alcohol, commenc- 
 ing with weak methylated spirit and finishing in absolute 
 alcohol ; lung in chromic acid, muscle in chromic acid, as 
 well as tongue, stomach, and spinal cord the last in one 
 part of the stock solution diluted with nine of water, as it 
 is extremely liable to over-hardening. The actual opera- 
 tion of hardening may be performed in the following 
 manner : Cut the substance kidney, for instance into 
 pieces half an inch square, and about the length suitable 
 for the well of the microtome. Place these in methylated 
 spirit diluted with an equal bulk of water for three days, 
 drain well upon bibulous paper, and then immerse in a 
 solution of chromic acid prepared by diluting one part of 
 the stock solution with seven parts of water. Allow the 
 pieces to remain in this for three days, then pour it off and 
 replace it by fresh. At the end of ten days a piece may 
 be abstracted and a rough section cut in order to see whether 
 it has become sufficiently hardened; if not, the chromic 
 acid must be again poured off and the pieces covered with 
 fresh solution, making an examination of it with the razor 
 every three days. Always harden insufficiently in the 
 chromic acid, and when just under that degree required, 
 take it out and put into methylated spirit to cleanse. 
 
1 92 PRACTICAL MICROSCOPY. 
 
 Pour off the spirit every day and replace it with fresh 
 until the excess of chromic acid has been abstracted, known 
 by the spirit remaining clear and colourless. 
 
 Injected kidney, and, indeed, most other injected tissues, 
 must be hardened entirely in alcohol, as the chromic acid, 
 being a powerful oxidiser, would in all probability cause a 
 decomposition of the colouring matter. Kidney is often 
 injected with Prussian blue. In this case it is as well to add 
 a few drops of hydrochloric acid to the alcohol used in 
 hardening. 
 
 The hardened tissue is now ready for cutting, and this 
 operation may be illustrated by employing the Rutherford 
 microtome, illustrated in Fig. 174. 
 
 The substance when taken out of the spirit must be 
 placed on blotting paper, and allowed to become surface 
 dry. When this is effected it must be dipped into the gum 
 solution before mentioned, and, after removal, is to be again 
 laid upon the paper until dry. 
 
 The microtome having been screwed to the table, and the 
 plug lowered by means of the screw, the melted mixture of 
 naphthalin and stearine is to be poured into the well. 
 When just about to set, the substance is inserted carefully, 
 and held in position until the bedding has sufficiently 
 solidified. After an hour or more, according to the tempera- 
 ture of the atmosphere, the substance will be in a fit state 
 for cutting, and may be performed in exactly the same 
 manner as described for vegetable stems. 
 
 The section knife is best kept in order on an ordinary 
 razor-strop, with an occasional touch on a fine Washita oil- 
 stone. 
 
 Fig. 179 shows a longitudinal section of the injected 
 kidney of a rat, a being the arterial trunk, b the venous 
 trunk, and c the glomerulus ; while Fig. 180 is a section of 
 human muscle showing Trichina spiralis in situ. 
 
CUTTING ANIMAL SECTIONS. 
 
 193 
 
 Rutherford's microtome is also capable of being used as 
 a freezing instrument, in a manner easily understood by 
 reference to the ac- 
 companying illustra- 
 tion, it being a section 
 of the instrument 
 already figured. 
 
 The freezing box 
 is surrounded with 
 several layers of 
 flannel, and the ma- 
 chine screwed to the 
 table. The plug 
 K being unscrewed, 
 pour methylated spirit 
 into the tube C, oil 
 the sides of the plug, 
 replace it, and depress 
 the screw to the desired extent. Remove all spirit which 
 has come above the plug K, and carefully close the margin 
 with some hog's-lard to pre- 
 vent the spirit reaching the 
 cavity above the plug. 
 
 The embedding fluid is 
 made by soaking five 
 ounces of picked gum 
 arabic in ten ounces of 
 water, and when it has 
 dissolved add two drachms 
 of camphorated spirit and 
 one drachm of glycerine, 
 after which it is to be strained 
 through calico, and kept in a bottle, free from dust. This 
 mixture, when frozen, cuts very much like a Gruyere cheese. 
 
 O 
 
 FIG. 179, 
 
 FIG. 180. 
 
194 
 
 PRACTICAL MICROSCOPY. 
 
 In working, place in the freezing box alternate layers of 
 finely powdered ice and common salt, taking care that they 
 are pushed well round the tube of the machine ; attach an 
 indiarubber tube to H and conduct the water into a jar or 
 pail, seeing also that it is kept open in order that the liquid 
 may find easy egress. The mixture of ice and salt must 
 be added at intervals, and the contents of the box stirred 
 occasionally with a short rod in order to promote the 
 escape of fluid. 
 
 FIG. 181. 
 
 The gum solution is run into the well of the microtome 
 and covered with a piece of guttapercha ; when the film of 
 ice has formed at its periphery, the tissue should be held 
 against the advancing film until it becomes fixed in 
 position for easy section. The razor used should be of 
 the form already described (R, Fig. 181), and when in 
 
SLITTING AND POLISHING BENCH. 195 
 
 use with the freezing microtome it will be unnecessary 
 to wet it. 
 
 The top plate would be better made of steel, or even 
 of glass, unless razor-guards be used, as though it is 
 easy after some practice to prevent cutting into the brass, 
 yet this invariably happens to beginners. Do not forget 
 to well wash the microtome and knife before putting 
 them away, and to grease them with some heavy lubri- 
 cating oil. 
 
 We now come to the preparation of sections of hard sub- 
 stances, such as bone, coal, rocks, and minerals generally. 
 Some operators start with a fragment chipped from a 
 large specimen ; but without doubt when several sections 
 have to be cut, the 
 best plan is to resort 
 to what is termed 
 slitting, being done 
 by the microscopist 
 himself or sent to the 
 lapidary, who will cut 
 slices for a very small 
 charge. 
 
 If the operator 
 desires a bench of 
 his own, it would be 
 advisable to have the 
 slitter and laps inter- 
 changeable, so that 
 they may run on the 
 same centres. The 
 
 Fir 
 
 woodcut, Fig. 182, will 
 
 show how such a bench may be constructed. 
 
 The slitter is a thin wrought-iron disc about 1 1 inches in 
 diameter by about A of an inch in thickness, and when used 
 
 O 2 
 
196 PRACTICAL MICROSCOPY. 
 
 its edge is charged with diamond dust in the following 
 manner: Reduce a small splinter of diamond to a fine 
 powder on a hard steel plate, then run a small quantity of 
 tallow on to it, and mix thoroughly with the steel crusher. 
 Press the tip of the longest finger into the mixture, bringing 
 away a thin coat. The slitter should then be moistened 
 with petroline, and a bloodstone or agate pressed gently 
 against it ; at the same time the finger should be brought 
 over the revolving disc in such a position that the edge may 
 just scrape the tallow off. This should be evenly distributed 
 round the edge of the disc, which is readily done by rapidly 
 touching it while revolving. 
 
 The rock, fossil wood, or other mineral, is now to be 
 ground flat on one side, and firmly cemented by old balsam 
 or marine glue (solid) to a glass slide, say 3x2 inches and 
 inch thick. This can readily be slid along the guide- 
 plate B, insuring perfect parallelism, the requisite thickness 
 of each section being regulated by the screw C, which 
 raises and depresses the guide-plate. The sections may be 
 about Tg- of an inch in thickness, more or less, according to 
 the subject, but the thinner they are cut, so much more 
 labour is saved in the subsequent operations. The sound 
 indicates when the slitter is cutting properly. 
 
 One side must be ground down on the leaden lap, which 
 may be substituted for the slitting disc A in the bench 
 shown in Fig. 182. This lap is about 10 inches in 
 diameter and f of an inch thick ; it is used with fine 
 emery and water for the first grinding, the final being 
 performed with still finer emery upon a ground brass 
 lap, preferably made to run in the same direction as the 
 face-plate of a lathe in fact, one of the cheap lathes 
 shown in Fig. 183 will do exceedingly well for this. work, 
 and no doubt the ingenious student will be able to rig 
 up a slitter and leaden lap to fit this form of lathe, 
 
TANGY&S LATHE. 
 
 IQ7 
 
 which may be made a very useful tool by the practical 
 microscopist. 
 
 In the grinding operation the student must remember 
 that a polish is not necessary. The Canada balsam in 
 which the section is mounted produces an apparent polish. 
 
 FIG. 183. 
 
 All that is required is to produce a very smooth surface 
 free from scratches, and this is readily done with a brass 
 lap and the finest emery procurable. The one side of the 
 specimen having been brought into the above condition, is 
 to be cleaned and firmly cemented with old balsam to the 
 centre of a 3 x i-inch glass slide. The balsam is dropped 
 upon the centre and warmed over a lamp until, when cold, 
 it is just possible to produce an impression with the nail. 
 
198 PRACTICAL MICROSCOPY. 
 
 The balsam is then to be rendered fluid again, and the 
 polished section made gradually hot, when it is let down 
 gently, taking care to avoid air bubbles, pressed down 
 firmly and then put aside to set thoroughly. After several 
 days, the rough side may be ground down on the leaden 
 lap with emery, and finished off on the brass lap with the 
 finest emery. The slide is now finished off by cleaning 
 with spirits of wine and a camel's-hair brush, then dropping 
 some fluid balsam upon the centre of the section and 
 covering in the usual way with thin glass. If the glass of 
 the 3 X I -inch slide be disfigured with scratches it may be 
 covered with an ornamental cover-paper, sold by Wheeler 
 and other dealers in microscopic specialities. The fore- 
 going method will produce good results for almost any 
 kind of work ; but of course there are simpler methods 
 which may suit the student, requiring however much more 
 labour. One of our friends grinds down roughly upon a 
 grindstone or emery wheel, and finishes upon an Arkansas 
 oil-stone. It is rather tedious work, but produces good 
 results. 
 
 Mr. J. H. Jennings gives the following simple instruc- 
 tions : 
 
 I. Preparing sections of hard rocks : In the first place a 
 thin chip must be procured by the use of a hammer. This 
 chip should be about I inch square, and not more than 
 \ inch thick ; chips of sedimentary rocks may be thicker. 
 Rub the chip down by hand with emery and water on an 
 iron plate, until one side is perfectly flat. To remove 
 scratches, next rub the chip on a glass plate with fine 
 emery, and polish on a Water-of-Ayr stone ; when quite 
 smooth, wash it well and let it dry. Meantime place 
 some old balsam on a glass slip, and warm it over a lamp 
 until all the more volatile parts of the balsam evaporate, so 
 that on cooling it becomes hard and tough. Do not let the 
 
CUTTING ROCK SECTIONS. 199 
 
 balsam boil. When the balsam is properly hard, warm the 
 chip gently over the lamp or on a hot metal plate, brush it 
 over with a little turpentine, and re-melt the balsam ; then 
 lower the chip slowly into the balsam until it is cemented 
 firmly and evenly by its flat surface to the glass slip. When 
 the balsam is quite cold, the chip is to be rubbed down on 
 the iron plate with coarse emery until it is too thin to bear 
 any further rough friction. With care, many rocks may be 
 brought to the requisite thinness on the iron plate alone, 
 and will require little finishing. The necessary degree of 
 thinness will vary according to the nature of the rock ; but, 
 as a general rule, most hard rocks must be cut thin enough 
 to read through when placed on the page of a book. When 
 the section will no longer bear the friction of the coarse 
 emery, remove it to the glass plate, and grind it thinner 
 with flour emery, and finally finish it off on the Water-of- 
 Ayr stone. The slide, at the finish, will be disfigured by 
 deep scratches from the emery, and the section must be 
 transferred to a clean slip. Warm the section enough to 
 melt the balsam, and push the section off with a needle 
 into a cup of turpentine, and wash carefully with a small 
 brush. Now pour a little balsam and benzol solution on 
 the clean slip, place the section upon it, add a little more 
 balsam, and cover. 
 
 2. Preparation of soft rocks and sedimentary rocks gene- 
 rally : These are prepared and mounted in the same way 
 as hard rocks, but no emery is to be used ; they must be 
 ground down and finished on the three stones mentioned 
 above. Some very friable rocks will require a preliminary 
 hardening by immersion for some days in a solution of 
 (i) balsam in benzol. The balsam must be first baked in a 
 cool oven, until on cooling it becomes hard and brittle ; 
 then dissolve it in benzol ; or (2) in a solution of shellac in 
 alcohol. This is, perhaps, the better of the two. When 
 
200 PRACTICAL MICROSCOPY. 
 
 the chip has remained long enough in the solution it must 
 be dried in a warm place. Sedimentary rocks, as a rule, 
 do not require to be cut as thin as igneous rocks, so that 
 they may be left on the grinding slide, as it will not be 
 scratched. 
 
 One thing is absolutely necessary in either method, that 
 is to get rid of all air bubbles in the balsam attachment, 
 as if any are left, the section is sure to wear into holes and 
 break. 
 
 Sections of Echinus spine may be cut in the same way as 
 above, or with a fine saw improvised from a thin clock 
 spring, and the slice ground down by rubbing on a fine 
 level Turkey hone, and when thin enough should be 
 cleansed with water and a soft camel-hair brush, dried by 
 immersion in alcohol, passed through benzol, and finely 
 mounted in balsam and benzol, or dry, if required, when it 
 is ready for observation. 
 
 Hard rocks, as a rule, are easier to prepare than soft 
 ones. The latter should be soaked in turpentine, and then 
 in balsam arid benzol, afterwards being heated till quite 
 hard. 
 
 Coal may be cut and ground into sections in the follow- 
 ing manner : After careful selection of a piece free from 
 cracks, a prism is to be cut J inch or f of an inch square. 
 Slices of this, as thin as possible, may now be cut with a 
 fine saw, and one face rubbed flat upon a slab of pumice- 
 stone kept well wetted with water, and finally rubbed 
 smooth upon a Water-of-Ayr stone, water being continually 
 applied to it. The polished surface is now cemented to a 
 3x1 glass slide with marine glue, taking special care not 
 to include air bubbles, and the slide put by to set for some 
 days. When this has taken place, the slice may be rubbed 
 down on a flat piece of coarse gritstone with plenty of 
 water until almost thin enough to show the structure, and 
 
CUTTING BONE AND TEETH SECTIONS. 2OI 
 
 when arrived at this stage, finished off first on the pumice 
 slab with water, and finally on the Water-of-Ayr stone. 
 
 The study of coal sections gives us much insight into the 
 formation of that peculiar substance. Fossil fungi have 
 been found in coal, and described by Mr. Worthington 
 Smith as belonging to the genus Peronospora, and the 
 plants have therefore been called Peronosporites. They are 
 shown in Fig. 184. 
 
 Bone and teeth are generally cut with a saw, and after- 
 wards rubbed down with a hone and water. Dr. Beale 
 
 FIG. 184. 
 
 objects to this method, as filling up the lacunae and 
 canaliculi with debris, and advises cutting a thin section 
 with a sharp knife, afterwards staining with carmine. Mr. 
 George Hoggan described a machine for cutting sections of 
 hard substances to the members of the Quekett Club, in 
 which he stated that each section was cut in two or three 
 minutes, which, after brushing away the sawdust, was ready 
 for mounting in balsam. 
 
 A few months since, Dr. Matthews described a machine 
 for a similar purpose at a meeting of the Royal Micro- 
 scopical Society, an illustration of which is shown in 
 
202 
 
 PRACTICAL MICROSCOPY. 
 
 Fig. 185. Such a machine is clearly only intended for 
 specialists, and therefore a full description of it would be 
 out of place here. 
 
 Dissections and section-cutting are generally looked 
 upon by the student with awe, as being exceptionally 
 difficult. This is not the case : with proper care and perse- 
 verance almost any one may become an expert dissector or 
 section-cutter, and it is to be hoped that whoever purchases 
 a microscope through reading these pages will endeavour 
 
 FIG. 185. 
 
 to do some useful work, and not be content with mounting 
 a few crystals for the polariscope, or with soaking an insect 
 in potash, and mounting in balsam, believing that is all 
 that need be done with it. 
 
CHAPTER IX. 
 
 THE DELINEATION OF OBJECTS MICROSCOPIC 
 MEASUREMENTS. 
 
 WE have now to dilate upon the importance of sketching 
 everything of interest the observer may see under the 
 microscope. 
 
 Dr. Beale says: "The student cannot too soon try 
 to delineate what he demonstrates. He will teach himself 
 to observe the more accurately and the more quickly if he 
 record the results of his work in pencil sketches. A truthful 
 drawing of what a man has recently seen may be compared 
 with drawings made 100 years hence ; and although the 
 means of observation will be more perfect than they are at 
 present, such comparisons may be useful in many ways, 
 and especially in preventing erroneous conclusions from 
 becoming popular." 
 
 It cannot be too strongly impressed upon the reader, of 
 the advisability of frequent practice with the various 
 means devised for this purpose. Microscopical contribu- 
 tions to our scientific papers, communications to societies, 
 and even the results of our every-day observations, all 
 become more interesting if illustrated in some way or 
 other. 
 
 There are many methods by which microscopical objects 
 may be delineated. They may be roughly drawn by means 
 of pencil and paper, guided by the eye alone or assisted 
 with the use of a circle of glass ruled into squares, made to 
 rest upon the diaphragm of the eye-piece ; the paper, in 
 
2O4 
 
 PRACTICAL MICROSCOPY. 
 
 this case, may also be faintly ruled into squares, and by 
 this means, especially after a little practice, very accurate 
 drawings can be made. Enlargements and reductions can 
 also be just as easily 
 drawn. A glance at 
 Figs. 1 86 and 187 will 
 illustrate this. The for- 
 mer represents what the 
 observer is supposed to 
 see upon looking down 
 the eye-piece of the 
 microscope ; while the 
 latter delineates the 
 figure produced by the 
 
 pencil upon the ruled 
 
 FIG. 186. 
 paper. 
 
 FIG. 187. 
 
NEUTRAL TINT REFLECTOR. 205 
 
 Another method for the delineation of objects is by the 
 use of the camera-lucida or neutral tint reflector, which by 
 a little practice becomes a very accurate process. The 
 ordinary camera-lucida consists of a prism, and apparently 
 throws down an image of the object upon the paper below it. 
 
 This is the same with the neutral tint reflector ; it is 
 made of a small piece of plate 
 glass, slightly coloured and arranged 
 at an angle of 45 with the eye- 
 piece ; it is shown in Fig. 188. 
 
 There is a fault with nearly all 
 reflectors hitherto made ; the glass 
 is too thick, and consequently two 
 or more images are formed of the 
 object, which come into view by FIG. 188. 
 
 a slight movement of the head. 
 
 To remedy this, a writer in ' Science-Gossip ' proposed a 
 head-rest, but even this may be dispensed with if the glass 
 used be of the same thickness as an ordinary cover, such 
 as is used in the mounting of objects. In the construction 
 of a reflector for drawing purposes, it is only necessary to 
 hold a thin glass cover at an angle of 45 with the eye- 
 glass, in such a position that the centre of the cover coin- 
 cides with the optical axis of the microscope. Surely 
 students interested may manage to do this for themselves. 
 
 When using either the camera-lucida or the neutral tint 
 reflector, the cap is removed from the eye-piece and the 
 accessory placed in its stead, the microscope arranged hori- 
 zontally, and the paper placed under it upon the table, as 
 shown in Fig. 189. 
 
 The instrument shown is one of Messrs. Ross's make, 
 and is nicely balanced in all positions. Messrs. Swift and 
 Son place a stop on most of their stands, so that it is easily 
 known when the body is either horizontal or vertical. 
 
2O6 
 
 PRACTICAL MICROSCOPY. 
 
 The most important point to be remembered in the use 
 of these reflectors is the proper management of the light. 
 Perhaps the student will fail at first in seeing together the 
 pencil and the object, but this difficulty will vanish upon 
 securing the proper illumination. The light must not be 
 concentrated too strongly upon the object, neither should 
 the paper be placed entirely in the shade, the student soon 
 arriving at the happy medium after a few trials. 
 
 FIG. 189. 
 
 In order to obtain the same degree of amplification upon 
 the paper as appears when looking down the tube of the 
 instrument, the paper must be placed at the same distance 
 from the camera-lucida as that accessory is situated from 
 the objective front ; but the magnification is generally 
 expressed at a distance of 10 inches. 
 
 Another form of this instrument is Nachet's, for use with 
 vertical microscopes, with the ordinary pattern when used 
 vertically with immersion lenses or in any other position of 
 the instrument. 
 
CAMERA-LUCIDA. 2O/ 
 
 A diagram of this form is shown in Fig. 190, from which 
 the reader will see that it consists of a prism of nearly 
 rhomboidal form placed with one of its inclined sides over 
 the eye-piece of the micro- 
 scope. To this is cemented 
 a segment of a small glass 
 cylinder, constituting the com- 
 plete apparatus. This enables 
 sketches to be made with the 
 microscope body disposed 
 vertically with the greatest 
 ease, as although the ordinary 
 camera-lucida or neutral tint 
 
 reflector can be used with the 
 
 FIG. 190. 
 microscope in this position, 
 
 still drawing from it in this way is not a comfortable 
 operation. 
 
 A camera-lucida somewhat similar to the above is made 
 by Mr. Swift and shown in Fig. 191 ; it can also be used at 
 any inclination of the optical tube of the microscope. 
 
 There is another method by means of which microscopic 
 objects may be faithfully delineated, and that is by photo- 
 micrography. This art is usually con- 
 sidered a difficult one, and when we are 
 confronted with the fact that nearly all 
 who have written anything upon the 
 subject have advised the use of a host 
 of complicated paraphernalia, it is 
 scarcely surprising that such an opinion 
 should have gained ground. The vast 
 array of apparatus, condensers of peculiar construction, 
 blue cells, heliostats, and even to a special room set apart 
 for the camera alone, must have been quite sufficient to 
 frighten any one with only their evenings at leisure. 
 
208 
 
 PRACTICAL MICROSCOPY. 
 
 An ordinary microscope and photographic camera, as 
 shown in Fig. 193, is all that is absolutely required for this 
 work, though with some it may be more convenient to use 
 the apparatus illustrated by Figs. 192 or 195. 
 
 The camera proper is made to remove from the base- 
 board, but this is for portability only. The base-board 
 should project for some distance in front of the camera to 
 carry the microscope and illuminating apparatus as in Fig. 
 193, so that the whole may form a solid continuous base. 
 This is necessary, as well as a good firm table upon 
 which to place the apparatus, and this must be quite free 
 from any vibration to insure perfect sharpness of the 
 image. 
 
 Of course the length of the base-board and of the camera 
 body when extended must vary with the amplification re- 
 quired. The diameters to which an object is enlarged in 
 the camera (Fig. 192) when the sensitive plate is at a distance 
 of 36 inches from the object, may serve as a guide in this 
 direction. 
 
 
 
 Diameters. 
 
 
 
 Designation. 
 
 Without Eye-piece. 
 
 With the A Eye- 
 piece. 
 
 
 
 4 inch 
 
 2 
 
 
 
 12 
 21 
 
 16 
 
 
 
 i 
 
 
 
 
 I 
 
 no 
 
 240 
 
 
 
 
 
 
 
 173 
 
 520 
 
 
 
 
 
 
 
 360 
 
 1000 
 
 
 
 
 
 
 
 530 
 
 1600 
 
 
 If the operator prefers to work with the eye-piece in 
 addition to the objective, the camera need only be a 
 short one, say extending from four inches to twelve, the 
 apparatus being arranged as shown in Fig. 193. At this 
 latter distance he will get the same degree of amplification 
 
PHOTO-MICROGRAPHIC APPARATUS. 
 
 209 
 
 as when looking down the tubes of his microscope, and the 
 author has but few doubts whether, after all, despite adverse 
 criticisms, this is not the simplest and cheapest plan. He 
 
 FIG. 192. 
 
 has both taken, and seen taken, photo-micrographs of the 
 same subjects, with and without the use of eye-pieces, and 
 could not discover any difference between them. 
 
 FIG. 193. 
 
 There is more light lost when working with the eye-pieces 
 attached, but in these days of extra-sensitive plates this is 
 certainly no disadvantage with the lower and medium 
 powers. 
 
 The microscope employed may be of any ordinary kind, 
 monocular preferably, and if provided with a means of 
 shortening the tube or body so much the better. The 
 tube should be lined with velvet, to prevent central flare, 
 
 P 
 
210 PRACTICAL MICROSCOPY. 
 
 and the instrument provided with a coarse and fine adjust- 
 ment, the latter answering the helm when turned either 
 backwards or forwards ; but more particularly must it be 
 sensitive to very slight movements of the milled head when 
 withdrawing the objective from the stage. 
 
 Dr. Woodward states " the objective selected should 
 always be specially corrected for photography." The 
 author is not able to agree with Dr. Woodward on this 
 point ; no doubt it is very convenient to have one so 
 corrected, but it is by no means imperative. To those as 
 yet uninitiated in the mysteries of the photographic art, it 
 may be necessary to say that the visual and actinic foci 
 often (though not necessarily) lie in different planes, and 
 therefore an objective which gives perfect definition to the 
 eye will often produce a blurred and indistinct image upon 
 the sensitive plate. This may be remedied in withdrawing 
 the objective, by turning the milled head of the fine adjust- 
 ment ; it cannot be told beforehand what allowance is 
 necessary, the only method is by trial and error; some 
 objectives require no correction whatever, while others 
 which necessitate considerable movement from the object, 
 can be made to yield just as perfect results. 
 
 The best way to arrive at the necessary correction is to 
 take a picture at the best visual focus, develop, fix, and dry 
 in the usual manner, and then withdraw the objective from 
 the stage by means of the fine adjustment until the image 
 appears on the ground glass about as indistinct as it does 
 in the negative. This will probably be the amount of cor- 
 rection required, and one or two trial plates will decide the 
 question. For powers up to the half-inch the proboscis of 
 the fly (Fig. 99) is a good object to experiment with ; 
 a photograph of this preparation, taken with a Ross's 
 ij-inch, showed that its actinic focus was identical with 
 
METHODS FOR FOCUSSING. 
 
 211 
 
 its best visual, while a 2-inch, by Dancer, required one 
 complete revolution of the milled head of the fine adjust- 
 ment. 
 
 Ordinary ground glass is too coarse to focus upon ; two 
 surfaces should be rubbed together with a little of the 
 finest emery and water, or a focussing glass may be 
 prepared by coating an ordinary glass plate with the follow- 
 ing varnish : 
 
 Gum mastic 40 grains 
 
 Gum sandarac 1 60 grains 
 
 Ether 4 oz. 
 
 Benzol i^ oz. 
 
 J 
 
 The correct focus may be obtained by the eye alone, 
 though this is difficult, especially with high powers; and, 
 therefore, it is advisable to em- 
 ploy a magnifier of some de- 
 scription an engraver's lens or 
 an ordinary eye-piece with the 
 eye-glass removed as shown in 
 Fig. 194. The field lens is 
 placed next the eye and the 
 open brass tube slid in a pa- 
 rallel direction over the glass 
 focussing screen. 
 
 The author now uses a much 
 improved method for focussing : 
 removing the ground glass 
 slide another is substituted of 
 
 FIG. 194. 
 
 mahogany, but pierced with a series of seven holes, into 
 each of which the ordinary A eye-piece may be fixed. 
 The thickness of the slide is such that when the eye- 
 piece is pushed in as far as it will go the diaphragm 
 lies in the same plane as the ground surface of the 
 
 P 2 
 
212 
 
 PRACTICAL MICROSCOPY. 
 
 glass slide. To any one accustomed to focus by the old 
 method the present system will be found a consider- 
 able improvement, it being easy under these conditions to 
 obtain a sharp focus with an ordinary paraffin lamp when 
 using the T V objective. (See Fig. 193.) 
 
 The microscope stand employed by the author possesses 
 a fine adjustment, moving the objective -^-^ of an inch 
 for each revolution of the milled head, and is divided into 
 twenty parts. His objectives require the following cor- 
 rections : 
 
 ] 
 
 Designatio 
 
 n. 
 
 
 Maker. 
 
 Air Angle. 
 
 Correction. 
 
 4-in< 
 
 :h .. . 
 
 
 
 Browning 
 
 9 
 
 o-oioo inch 
 
 2 , 
 
 
 
 
 Dancer 
 
 14 
 
 o'oo5o ,, 
 
 I , 
 
 . . 
 
 
 
 Browning 
 
 25 
 
 0-0025 ,, 
 
 2 J 
 
 .. 
 
 
 
 Browning 
 
 60 
 
 0-0005 
 
 4 > 
 
 
 
 
 Browning 
 
 85 
 
 
 
 i: 
 
 
 
 
 Browning 
 Dancer 
 
 140 
 170 
 
 
 
 
 The source of illumination may be the ordinary micro- 
 scopical paraffin lamp, as the light from it is much more 
 actinic than that of gas, and for all powers below the 
 J-inch it is only necessary to use the bull's-eye condensers 
 as shown in the figures. 
 
 A very intense illumination, for photo-micrography, may 
 be obtained from paraffin oil by using it in a triple-wick 
 lamp, such as the Triplexicon or Sciopticon, with a con- 
 denser parallelising the rays proceeding from it, as shown 
 in Fig. 195. These parallel rays are again to be converged 
 by a convex lens of 3 inches diameter and 10 inches focus. 
 Such an arrangement as used by the author is shown by 
 Fig. 195, and by means of it the relative lengths of 
 exposure have been very much shortened. 
 
 With the objectives already alluded to, the sensitive 
 plate being at a distance of 24 inches from the object, with 
 
WET AND DRY PLATES. 
 
 213 
 
 an ordinary paraffin lamp and bull's-eye condenser of 
 3 inches focus, the shortest exposures for good pictures 
 
 FIG. 195. 
 
 with Mawson and Swan's "15 times" sensitive plates have 
 been found as follows : 
 
 
 
 Exposures. 
 
 Designation 
 of Objective. 
 
 Subject. 
 
 
 By Method 
 
 By Method 
 
 
 
 Fig. 192. 
 
 Fig. 195- 
 
 4- inch 
 
 
 Wing of blow-fly 
 
 
 
 
 6 seconds 
 
 3 seconds 
 
 2 
 
 
 
 Proboscis of do. 
 
 
 
 
 60 
 
 > 
 
 10 
 
 
 I 
 
 
 
 Do. do. 
 
 
 
 
 70 
 
 
 20 
 
 
 * 
 
 
 
 Glass crystal 
 
 
 
 
 60 
 
 > 
 
 3 
 
 
 i 
 
 
 
 Section of deal . . 
 
 
 
 
 7 min 
 
 utes~ 
 
 2 min 
 
 utes 
 
 i 
 
 
 
 Podura scale 
 
 
 
 
 10 
 
 ? 
 
 2j 
 
 
 A 
 
 
 
 Pleurosigma attenuatum 
 
 
 
 15 
 
 J 
 
 3 
 
 
 Dr. Carl Setter, in a communication to the ' American 
 Journal of Microscopy' upon this subject, seems to prefer 
 wet plates to dry ones, and adduces arguments in support 
 of his views, one of which is cheapness. The cost of plates 
 by the wet or dry process is so small that this item need 
 not enter into the calculation ; moreover, dry plates are 
 rapid, so convenient, and with good manipulation give such 
 excellent results, that the author pleads for the use of them 
 exclusively in producing negatives. 
 
 There are many kinds of dry plates to be met with in the 
 market, nearly all of which are now prepared from gelatine 
 
214 PRACTICAL MICROSCOPY. 
 
 emulsion. Mawson and Swan's, having been extensively 
 used by the author for this kind of work, deserve commen- 
 dation as being of good and uniform quality. 
 
 Do not over-expose these gelatine plates, or you will get 
 nothing but thin and misty images. From some cause, 
 those exposed to gas or lamp-light do not commence to 
 develop so quickly as those exposed to sunlight ; but if 
 time is given, and they are not over-exposed, perfect 
 pictures may easily be obtained. The time of exposure in 
 the camera depends upon the quality of the light, but more 
 perhaps ttpon the nature of the object than anything else ; for 
 instance, a section of the kidney of a horse required twenty 
 minutes' exposure with the argand gas and bull's-eye con- 
 denser, while a crystal of glass under the same conditions 
 of light and amplification required but one minute. 
 
 For ascertaining the exact exposures and the corrections 
 required for the difference in actinic and visual foci, the 
 beginner is strongly advised to keep a bound record of his 
 failures as well as prints from all his negatives, with full 
 particulars respecting them ; they are great helps in photo- 
 graphing new subjects. 
 
 Mr. Dancer of Manchester, Dr. Maddox, Mr. Shadbolt, 
 the late Dr. Redmayne of Bolton, Mr. Wenham, and 
 several others have been the most successful photographers 
 of microscopic objects ; not forgetting, however, Colonel 
 Dr. Woodward in America, as most of the photographs 
 and nearly the whole of the literature of this country has 
 emanated from him. 
 
 Dr. Woodward has described his method with sunlight 
 and a heliostat, from which we gather the following : 
 
 The microscope being placed on a shelf at the window of 
 the dark room, and its body made horizontal, the achro- 
 matic condenser is illuminated by a solar pencil reflected 
 from a heliostat (Fig. 196) upon a movable mirror outside 
 
PHOTO-MICROGRAPHY BY SUNLIGHT. 
 
 215 
 
 the shutter, and thence into the dark room. No ground 
 glass is used, but a lens mounted in a suitable tube is fixed 
 in the opening of the shutter through which the solar pencil 
 enters. This lens is an achromatic combination about 
 2 inches in transverse diameter and of about IO inches 
 focal length. It is placed at such a distance from the 
 achromatic condenser that the solar rays are brought to a 
 focus and begin again to diverge before they reach the 
 lowest glass of the achromatic condenser. 
 
 FIG. 196. 
 
 All trouble from the solar heat is thus completely 
 avoided. So successfully may this be done, that it is 
 possible to obtain light enough to give distinct vision and 
 admirable definition on the cardboard screen with 5000 
 diameters, while the heat is so slight that the drop of water 
 used with the immersion lens does not require renewal 
 oftener than about once in two hours. 
 
 For anatomical preparations requiring for their display 
 from 200 to 500 diameters, the ^-inch objective may be 
 used without an eye-piece, obtaining the precise power 
 desired by variations in the distance of the sensitive plate 
 
2l6 PRACTICAL MICROSCOPY. 
 
 from the stage of the instrument. Dr. Woodward gives 
 the preference to immersion objectives, the corrections of 
 which are generally well suited to photographic require- 
 ments. 
 
 With a \ objective and the arrangement above de- 
 scribed, the field is so brilliantly illuminated that the eye 
 cannot safely be permitted to look down the tube. The 
 image is therefore received on a piece of white cardboard, 
 and, sitting by the microscope to make the adjustment, the 
 card is viewed with both eyes, precisely as in the case 
 of the ordinary solar microscope. 
 
 When all is satisfactory, an ammonio-sulphate cell is 
 inserted between the large lens and the achromatic con- 
 denser, and the velvet hood, which prevents leakage of light 
 from about the microscope into the dark room, is drawn 
 down.. 
 
 Dr. Woodward finds it best to use the naked objective 
 without eye-piece or amplifier, and not as a rule to fix 
 the sensitive plate more than 3 or 4 feet from the stage of 
 the microscope. A \ objective may be conveniently 
 employed to obtain powers of from 200 to 500 or 600 
 diameters; a T V for higher powers, up to 1200 or 1500 
 diameters. 
 
 It occurred to him that for such short exposure the 
 heliostat might be dispensed with, and on trial without it 
 found that a large right-angle prism used in the position of 
 total reflection, or even an ordinary mirror, gave excellent 
 results ; the exposures being even shorter than when the 
 heliostat was used, since there was but a single reflection. 
 Under ordinary circumstances the heliostat appears desir- 
 able for general use since, the solar pencil being thrown in 
 a constant direction, the trouble of adjusting the illumina- 
 tion of a series of objects is considerably diminished ; but 
 equally good pictures can be produced without it, even 
 
PHOTO-MICROGRAPHY BY ELECTRIC LIGHT. 21? 
 
 with very high powers, a circumstance of considerable 
 interest where motives of economy preclude the micro- 
 scopist from procuring this convenient instrument. 
 
 The time of exposure required for the production of 
 pictures magnified 500 diameters or less was about a 
 second. With higher powers it increases, varying with 
 the management of the achromatic condenser. For 4000 
 diameters as much as twenty-five seconds is sometimes 
 required. 
 
 In using the electric light it is necessary to render the 
 divergent pencil proceeding from the carbon points as 
 nearly parallel as possible, by means of the condenser 
 usually supplied with electric lamps for this purpose, and 
 then introduce into the parallel pencil, instead of a ground 
 glass, the very same condensing lens described above for 
 the process with solar light. The image is received 
 primarily for focussing on a cardboard screen, and the 
 
 FIG. 197. 
 
 remaining details do not differ from what has been 
 related above. The time of exposure does not exceed a 
 single second for 400 diameters, and the sharpness of the 
 pictures is excellent. For well-made tissue preparations, 
 however, the best work obtainable with the electric light is 
 so similar to the best attainable by sunlight, used as above 
 described, that it is scarcely necessary to take the trouble 
 
2 1 8 PR A CTICAL MICROS COP Y. 
 
 to set up the battery and work the electric lamp, unless 
 it was desirable to work at night or in unfavourable 
 weather. 
 
 For the production of the electric light, Duboscq's lamp 
 was used, set in motion by a battery of fifty small Grove's 
 elements, and with this source of light photographs can be 
 taken with any power with which pictures are possible 
 in sunlight. The rubber cups of the battery were 4! inches 
 high, 3J inches wide, and 2 inches thick ; the platinums 5^ by 
 2i inches, and weighed about 60 grains each. The zincs 
 were bent on themselves so as to present a part of their 
 surface on each side of the platinums, and weighed when 
 new about a pound each. 
 
 FIG. 
 
 The electric light as hitherto employed has been a 
 cumbrous, expensive, and troublesome process, which 
 certainly could not be employed by the majority of per- 
 sons wishful to practise photo-micrography. For those 
 who may have to use high powers, and to whom daylight 
 is not accessible, the magnesium light seems to possess 
 
PHOTO-MICROGRAPHY BY MAGNESIUM LIGHT. 2IQ 
 
 advantages. For this process a good lamp is necessary, 
 and the one shown in Fig. 198 is the best of its kind. 
 
 In describing the magnesium modification of photo- 
 graphy as applied to the amplification of microscopic 
 objects, Colonel Woodward compares the light given off 
 by a good magnesium lamp to white-cloud illumination of 
 the best character. 
 
 Without the use of ground glass, this light serves ad- 
 mirably for the production of photographs of soft tissue 
 with any power under 1000 diameters. The light being 
 composed of a mixed pencil, with rays passing in all 
 directions, there are no interference phenomena ; but for 
 the same reason, on the Nobert's plate and many test- 
 objects, the results are inferior to those produced by the 
 sun or by the electric light ; with powers much higher than 
 1000 diameters, however, the time of exposure becomes 
 inconveniently long. 
 
 FIG. 199. 
 
 The condenser concentrates the light on the lower lens of 
 the achromatic condenser of the microscope as shown in 
 Fig. 199, which stands on a table supported by three 
 levelling screws. The image is received on the plate- 
 holder supported on the table, and photographed precisely 
 
220 PRACTICAL MICROSCOPY. 
 
 as when using the sun's rays as before described. The 
 same focussing apparatus is employed, and the ammonio- 
 sulphate cell should invariably be inserted, but the ground 
 glass is never necessary. To produce negatives of tissue- 
 preparations with 500 diameters it requires exposures of 
 about three minutes. Other powers require proportionate 
 exposures. 
 
 Magnesium wire costs 12s. 6d. per ounce; two ounces 
 will, with care, answer for three or four hours' constant 
 work, and ought to produce from twelve to thirty nega- 
 tives, in accordance with the difficulties of the subjects to 
 be represented. The fumes of magnesia resulting from the 
 combustion are carried into a chimney five feet long, made 
 of a spiral wire covered with muslin, terminating in a muslin 
 bag, shown in the figure, in which the oxide condenses, while 
 the draught goes on through the interstices of the muslin. 
 
 The method of photographing such objects as Amphi- 
 pleura pellucida and Nobert's test-lines has also been 
 described by Dr. Woodward in a letter to M. Deby, a 
 vice-president of the Belgian Microscopical Society. Such 
 objects as the A. pellucida require the use of very oblique 
 light, which is obtained in the following manner : A parallel 
 pencil of solar rays, from the heliostat and plane mirror, is 
 intercepted by a blue cell and diaphragm, which only 
 allows a circular pencil of half an inch diameter to pass. 
 The light enters parallel to the optic axis of the micro- 
 scope, placed in the usual position for photography, but at 
 the lateral distance to the right or left of 3 inches. If 
 the light is intercepted by a large achromatic prism, of 
 a focal length of about 3 inches, the desired obliquity 
 can be obtained without difficulty. The best result is 
 obtained when the rays are concentrated to a focus upon 
 the object, and it is indispensable that the stage of the 
 microscope be as thin as possible. The illumination thus 
 
DEVELOPING THE IMAGE. 221 
 
 produced is in general sufficient to produce negatives by 
 the wet process up to 2500 diameters with three minutes' 
 exposure. Fig. 112 shows that difficultly resolvable diatom 
 the A.pellucida, under an amplification of 960 diameters. 
 
 After the sensitive plate has been exposed the necessary 
 length of time by either of the foregoing methods of illu- 
 mination, it is ready for development. It is, therefore, 
 taken into a room from which every trace of actinic light 
 has been excluded, and there the picture is brought to 
 view by the use of the developing solution. Nearly every 
 photographic manipulator has his own way of developing, 
 though the general principles are the same, but that given 
 by Messrs. Wratten and Wainwright for their instantaneous 
 dry plates will perhaps be found the most suitable for 
 photo-micrographical purposes. 
 
 STOCK SOLUTION A*. 
 
 Ammonia liquor, fort. I oz. 
 
 Potass bromide 60 grains 
 
 Water 2 oz. 
 
 DEVELOPER. 
 
 Pyrogallic acid . . 6 grains 
 
 Stock Solution A* 20 drops 
 
 Water 2 oz. 
 
 Lay the exposed plate in a dish of cold water to soak 
 while the pyrogallic acid is mixed. For each i or 5 x 4 
 plate use 6 grains of pyro., diluted with 2 oz. of water. 
 First pour off the water from the plate and apply the 
 pyro. solution, then add five drops of stock solution A*, 
 and keep this weak developer on the plate until the highest 
 lights are pretty well visible ; then add from 1 5 to 20 drops 
 more of A* to finish development. By this method more 
 of the film is employed and greater density is obtained. 
 Whenever any of solution A* is to be added to the pyro. 
 solution it should be first dropped into the developing cup, 
 
222 PRACTICAL MICROSCOPY. 
 
 and then, if the solution which is in the dish be poured back 
 to the cup a perfect admixture will be the result without 
 the necessity of stirring. With correct exposure full print- 
 ing density may be easily attained with the alkaline pyro. 
 alone. No plate is supplied that will not bear 100 drops 
 of stock solution A* without fog if the correct exposure 
 has been given. One thickness of deep ruby glass is unsafe 
 for the dark room ; two, at least, are necessary. Should any 
 discoloration of the film appear after the negative has been 
 fixed and washed, it may be cleared away with a weak 
 solution of perchloride of iron and water (about the 
 colour of pale sherry), the plate afterwards to be washed 
 thoroughly. 
 
 Ferrous Oxalate Development. Where it is not expressly 
 stated to the contrary, Swan's plates may be developed 
 either with ammoniacal pyrogallic acid or with ferrous 
 oxalate ; but it occasionally happens that one and not the 
 other of these developers must be used. When that is the 
 case, the fact is stated on the label of the packet. 
 
 Ferrous oxalate developing solution is best made as 
 follows : 
 
 SOLUTION A. 
 
 Neutral oxalate of potash 6J oz. 
 
 Water 25 oz. 
 
 SOLUTION B. 
 
 Sulphate of iron 2^ oz. 
 
 Water 7^ oz. 
 
 Sulphuric acid I to 2 drops 
 
 The two solutions A and B are kept in stock, and when 
 required for development three volumes of A are mixed 
 with one volume of B. 
 
 It is better to mix and use what is immediately required 
 for the development of a single plate, and not to use the 
 same solution for developing several plates. The two stock 
 
FERROUS OXALATE DEVELOPMENT. 22$ 
 
 solutions keep well, therefore any quantity of these can be 
 kept ready for mixing. The sulphuric acid is not essential 
 in the formula referred to ; it can be omitted. 
 
 The bromide of ammonium solution may be added to the 
 developer as a restrainer, to counteract over-exposure in the 
 same manner and under the same conditions as in develop- 
 ment with pyrogallic acid and ammonia. 
 
 This ferrous oxalate developer should be used in a flat 
 bath, precisely in the manner described for alkaline pyro- 
 gallic acid development During the operation the solution 
 must be made to wave to and fro over the plate, and the de- 
 velopment continued until the required density is obtained. 
 This will occupy about three minutes, as a rule. The addition 
 of bromide affects most powerfully the rate of development 
 and its character, making it slower and increasing the con- 
 trast of light and shade. For copying engravings, &c., where 
 only black and white is to be printed, the proportion of 
 bromide of ammonium may be advantageously increased. 
 
 If during development or fixing any loosening or blister- 
 ing of the film should be observed, the plate must be 
 immediately rinsed in water and put into a solution of alum 
 (i oz. to I pint of water). After allowing to remain five 
 minutes in the alum solution, it should then be finished as 
 usual after this treatment ; and as all plates of the same 
 packet will probably be alike, it will be advisable with each 
 of these to use the alum bath after development, without 
 waiting for the appearance of blisters or loosening of the 
 film. 
 
 The image generally makes its appearance in about a 
 minute, the deposit gradually increasing in intensity until 
 the development is finished. It is then to be well washed 
 and fixed in the following solution : 
 
 Hyposulphate of soda . . 4 oz. 
 
 Water . . . . ' . . 20 oz. 
 
224 PRACTICAL MICROSCOPY. 
 
 In cases where, from over-exposure, it has been impos- 
 sible to obtain density with the alkaline developer, a most 
 careful washing should be given after fixing, with a view to 
 remove the last trace of ammonia. 
 
 Intensification can then be effected with acid pyro. and 
 nitrate of silver, or with protosulphate of iron and' nitrate of 
 silver. The author has a decided preference for the latter, 
 and uses the following formula, viz. : 
 
 A. 
 
 Protosulphate of iron 15 grains 
 
 Gelatine- acetic acid solution (as described 
 
 below) 40 drops 
 
 Water I oz. 
 
 B. 
 
 Nitrate of silver 10 grains 
 
 Acetic acid, glacial, 50 10 drops 
 
 Water I oz. 
 
 The gelatino-acetic acid solution is compounded as 
 under: 
 
 Gelatine .. .. _ r . .. .. 15 grains 
 
 Acetic acid, glacial, 50 . . 3 drachms 
 
 Water .. .. .. 5 drachms 
 
 and it is well to prepare a stock of this, and also of A, as 
 they are both better for keeping. 
 
 To proceed first flood the plate with water and then 
 with a solution of iodine and iodide of potassium of the 
 colour otpale sherry for one minute, rinse it off, and apply 
 enough of A to cover the plate, for about the same 
 time. Now drop into the cup a drachm of B, and 
 bring the A back from the plate to the cup to mix them 
 together. Re-apply, and keep moving over the surface 
 until density is sufficient. If any air-bells should occur 
 they must be kept moving, and then they will do no 
 harm. 
 
FIXING VARNISHING. 22$ 
 
 Both development and intensification are best performed 
 in a dish the former in an ebonite, the latter in one of 
 porcelain. 
 
 When the plate has again become dry, warm and varnish 
 it as usual. 
 
 Fixing. It is well to finish fixing each plate by im- 
 mersing it for about ten minutes in a perfectly fresh hypo- 
 sulphite solution after the plate has, in the ordinary sense 
 of the word, been fixed that is, after the creamy appear- 
 ance of the film has been discharged by immersion in a 
 solution perhaps not quite fresh. The temperature of the 
 hyposulphite solution should not be below 50 nor above 
 70 F. The apparent change in the strength of the image 
 which attends fixing has led some to suppose that the 
 image is greatly weakened by the action of the hyposul- 
 phite solution ; but this is not the case, and we think it 
 important to state clearly that the hyposulphite solution 
 will not injure the image, even if it be allowed to act for a 
 very much longer time than is necessary for the thorough 
 fixation of the image and the removal of instable silver 
 compounds from the film. Time must be allowed, both for 
 the action of the hyposulphite of soda solution, and also for 
 thorough washing afterwards, in order to effect the com- 
 plete removal from the plate of compounds which, if not 
 removed, will ultimately destroy the plate. 
 
 Finishing the Plate. The plate must be dried spontane- 
 ously. On no account may artificial heat be applied. In 
 case of urgency drying may be hastened by immersion in 
 methylated spirit, and then varnished when dry. A suit- 
 able varnish for this purpose is Mawson and Swan's " dry 
 plate varnish." In every case the negative should be care- 
 fully preserved from damp. Enamel collodion is a useful 
 temporary varnish for negatives on gelatine plates. 
 
 Q 
 
226 PRACTICAL MICROSCOPY. 
 
 Having obtained a suitable negative, it is easy to print 
 from this either upon carbon tissue or the ordinary sensi- 
 tised paper, which latter may now be bought ready prepared 
 at I s. per sheet. It will keep in good condition for months. 
 
 After printing several shades darker than is finally 
 required, the prints are soaked in water to remove the free 
 nitrate of silver, and then put to tone in one of the following 
 
 baths : 
 
 I. 
 
 Chloride of gold .. .. 15 grains 
 
 Acetate of soda I oz. 
 
 Water 80 oz. 
 
 II. 
 
 Dissolve one 15-grain tube of chloride of gold in 2 oz. of water. 
 Take I drachm of this solution, add 5 grains of tungstate of soda 
 and pour in 3 oz. of boiling water. Use the bath ten or fifteen 
 minutes after mixing j one grain of gold chloride will tone a sheet 
 of paper. 
 
 III. 
 
 Chloride of gold 15 grains 
 
 Chloride of lime 15 grains 
 
 Precipitated chalk I teaspoonful 
 
 Water (boiling) 80 oz. 
 
 This may be used at once. 
 
 IV. 
 
 Chloride of gold 7$ grains 
 
 Perchloride of platinum 7i grains 
 
 Acetate of soda I oz. 
 
 Water 80 oz. 
 
 After toning, the prints must be well washed and trans- 
 ferred to the fixing solution, which should be of the same 
 strength as that used for fixing the negatives. The prints 
 should be allowed to remain in this solution for ten minutes, 
 after which they are transferred to water, and washed until 
 perfectly freed from all traces of the hyposulphite. 
 
 There are two applications of this art which may be of 
 great utility, viz. the preparation of wood-blocks for the 
 purpose of illustrating microscopical work and also for the 
 production of lantern transparencies. The greatest expense 
 
PHOTOGRAPHING ON WOOD. 227 
 
 in producing good illustrations is that of the artist, but if 
 the picture is put upon the wood the remainder of the work 
 is cheaply and expeditiously performed. One way of doing 
 this is to transfer an autotype carbon positive to the pre- 
 pared wood-block ; but to produce good pictures upon 
 wood it is better to employ the wet collodion process. 
 
 A slightly over-developed positive is produced upon glass 
 in the ordinary way, being developed with an iron developer, 
 and the film transferred to the wood-block in the following 
 manner : The block is first to be coated with a gelatine 
 solution made by soaking i oz. of Nelson's gelatine in 
 19 oz. of water for twelve hours, dissolving with heat and 
 stirring in a solution of 20 grains of chrome alum in 
 i oz. of water. When thoroughly incorporated, add suffi- 
 cient lampblack to form an even black coating upon the 
 wood. 
 
 If the block be first coated, it will be dry and ready to 
 receive the film by the time the operator has proceeded 
 thus far. The positive having been taken, developed, and 
 fixed, a piece of gummed paper is " squeezed " to the wet 
 film, which must then be stripped off the glass. The paper 
 and film may now be trimmed with the scissors, and 
 brought into contact under water with the prepared block, 
 gently squeezed to remove air and water, and set aside 
 for a while, so that the two films may become amalga- 
 mated. After a short time the block is soaked in tepid 
 water to remove the gummed paper, and after drying is 
 ready for the engraver. Many of the illustrations in this 
 work have been prepared by this process, and it is here 
 recommended to all who may read papers before the 
 members of the various societies with which they may be 
 connected. 
 
 In the preparation of transparencies for the lantern, it 
 is necessary first of all to secure a good and sharp nega- 
 
 Q 2 
 
228 PRACTICAL MICROSCOPY. 
 
 tive. This is placed above a dry plate, the two films being 
 in contact, exposed to the light in a printing frame, and 
 the latent image developed and fixed in the usual way. 
 The best dry plates with which to prepare transparencies 
 are the collodio-albumen, developed with pyrogallic and 
 citric acids, and next to these, any good collodion plate. 
 It is a very difficult matter to prepare brilliant trans- 
 parencies upon gelatine plates ; they are so extremely 
 sensitive to light that it is next to impossible to keep the 
 high lights clear and free from fog. Very passable pictures 
 may, however, be obtained from them by giving 12 seconds' 
 exposure, under a negative of ordinary density, to the light 
 of a common bat's-wing gas-burner. 
 
 The collodio-albumen plates, when developed with pyro- 
 gallic and citric acids, generally yield a fine blue-black 
 image; they may, however, be readily toned in a weak 
 solution of sulphide of ammonium, if requisite. 
 
 When dry the picture should be covered with another 
 piece of clear glass the same size, the two being prevented 
 from touching by very small strips of card fastened by 
 gum to two of the edges, the whole bound round with thin 
 black paper, and the slide is completed. These pictures, 
 when laid upon white paper, should only allow the paper 
 to show through in the very highest lights, just a patch of 
 white here and there. 
 
 For the illustration of papers read before societies, trans- 
 parencies prepared by the foregoing method may be shown 
 by the use of the Sciopticon or Triplexicon (Fig. 195), by 
 which means sufficient illumination can be obtained with 
 paraffin oil to produce a good disc 6 or 7 feet in diameter. 
 It is, of course, necessary by this method to first produce 
 an enlarged transparency of the object, which entails some 
 previous trouble, though it is less costly than that next 
 to be described. 
 
THE LANTERN MICROSCOPE. 229 
 
 Mr. Browning has prepared a nose-piece for lanterns, 
 which he calls the " Lantern Microscope," by the use of 
 which the ordinary 3 X i microscopic slides may be 
 displayed upon the screen. Its form may be seen in 
 Fig. 200. 
 
 FIG. 200. 
 
 It is composed of the following parts, conveniently 
 mounted in brass, with rack adjustments and other requi- 
 sites, and so arranged that it can immediately replace the 
 ordinary front combination of first-class lanterns: (i) 
 Lenses acting as an achromatic condenser, receiving the 
 light that passes through the large lenses of the lantern 
 and reducing the light-pencil to the proper size. (2) An 
 object-holder for 3 x I inch slides. Then follows the 
 magnifying apparatus, as in a table microscope namely, 
 an achromatic objective, made specially for this instrument, 
 and a Kelner eye-piece, giving considerable amplification 
 with a very wide field. The light-pencil must be adjusted 
 by means of the rackwork attached to the second con- 
 denser, and an image of the object to be displayed must be 
 received on a well-strained paper screen, and carefully 
 focussed by turning the milled head furthest from the 
 object. The objects best suited for display are transparent 
 injections, which should be thin and not too darkly stained ; 
 entire insects, mouth organs, tracheal tubes, &c., of the 
 larger kinds, sections of wood, tissues and organs of plants, 
 preparations of zoophytes, sections of coal and other 
 minerals. To prevent disappointment, it should be remem- 
 bered that transparent objects, such as diatoms and the 
 
230 PRACTICAL MICROSCOPY. 
 
 smaller infusoria, do not give sufficiently positive outlines 
 for this method of display. Neither oil lamps nor the 
 paraffin lamp of the Sciopticon or Triplexicon yield suffi- 
 cient light. For magnifications of from 50 to 100 diameters 
 lime-light will perform well, but for higher powers the 
 electric light should be used. 
 
 MiCROMETRY. The micrometer, as its name signifies, is 
 used for measuring small objects, and omitting all historical 
 notices which may, however, be found in the works of 
 Baker and Quekett we will proceed to describe those 
 forms most in use. 
 
 FIG. 201. 
 
 The stage micrometer consists of a glass slip such as is 
 shown in Fig. 201, upon which are ruled a series of lines 
 generally -j^j- of an inch apart, one of these divisions 
 being again divided into ten parts ; so that there is on the 
 same scale the means whereby objects of varying magni- 
 tude may be exactly measured, to less even than the 
 thousandth of an inch. 
 
 Some micrometers are also ruled to millimetres, tenths 
 and hundredths, and this system is daily coming more into 
 use. A standard system for measurements was long 
 required for scientific microscopical purposes, and by very 
 general consent the thousandth part of a millimetre has 
 been taken as this standard, and by some termed a micro- 
 millimetre ; while others, objecting to the prefix " micro," 
 which in electrical measurements means a millionth of the 
 unit, prefer to call the unit of the thousandth of a milli- 
 metre a micra. One thousand micras make one millimetre. 
 The following table, extracted from the 'Journal of the 
 
MICRA [i MICRO-MILLIMETRES. 
 
 231 
 
 Royal Microscopical Society/ may be of use to the 
 reader : 
 
 Fractions of 
 an inch. 
 
 Micras. 
 
 Fractions 
 of an inch. 
 
 Milli- 
 metres. 
 
 Micras. 
 
 Decimals 
 of an inch. 
 
 
 /* 
 
 
 mm. 
 
 A 1 
 
 in. 
 
 TooTTU 
 
 2-539977 
 
 3oo 
 
 028222 
 
 I 
 
 000039 
 
 9000 
 
 2'822I97 
 
 Too 
 
 031750 
 
 2 
 
 000079 
 
 8~07H) 
 
 3-I7497I 
 
 Too 
 
 036285 
 
 3 
 
 OOOIlS 
 
 TTToo 
 
 3*628539 
 
 ^i_ 
 
 6OO 
 
 -042333 
 
 4 
 
 000157 
 
 ^Woo 
 
 4'23329S 
 
 Too 
 
 050800 
 
 5 
 
 000197 
 
 WoTJo 
 
 5 '079954 
 
 TS$ 
 
 056444 
 
 6 
 
 000236 
 
 ToZTo 
 
 6-349943 
 
 4UO 
 
 063499 
 
 7 
 
 000276 
 
 3oW 
 
 8-466591 
 
 STo 
 
 072571 
 
 8 
 
 000315 
 
 Tope! 
 ToVo 
 
 12-699886 
 25-399772 
 
 IHTo 
 
 2~iTo 
 
 084666 
 IOI599 
 
 9 
 
 10 
 
 000354 
 000394 
 
 
 
 ^Uo 
 
 126999 
 
 
 
 
 
 TTo 
 
 169332 
 
 
 
 
 
 Tol) 
 
 253998 
 
 
 
 The stage micrometer cannot be used for direct measure- 
 ments with any save low powers, as it is necessary that the 
 lines be seen at the same time as the dimensions of the 
 object ; but indirectly very exact measurements may be 
 obtained. This may be accomplished by sketching the 
 outlines of the object lying upon the stage, using the 
 camera-lucida as shown in Fig. 189. The object is then to 
 be replaced by the stage micrometer, the lines of which are 
 drawn over the previous sketch, showing by simple inspec- 
 tion the magnitude of the object, or any part of it may 
 now be measured with a pair of compasses. 
 
 It should be borne in mind that amplifications are gene- 
 rally expressed at a distance of 10 inches, and this is 
 accomplished by placing the drawing slab horizontally 
 10 inches beneath the acute angle of the camera-lucida 
 prism. If the object is required to be of the same size as 
 it appears upon looking into the microscope, the distance 
 of the drawing slab from the acute angle of the prism must 
 be equal to the distance of that point from the objective. In 
 estimating the magnifying power of an objective, the stage 
 
232 PRACTICAL MICROSCOPY. 
 
 micrometer is employed and a sketch made of it upon the 
 drawing slab at a distance of 10 inches. If, upon measuring 
 these lines with an ordinary rule divided into inches and 
 tenths, the hundredth of an inch space corresponds to 
 one linear inch, it is clear that the object has been magnified 
 100 diameters ; while if the thousandth of an inch space 
 occupied half an inch on the rule, it would have been 
 amplified 500 diameters. 
 
 Eye-piece micrometers are of several kinds, the simplest 
 being a circle of glass ruled with a series of squares ^V to 
 TFJJ- of an inch (or T V of a millimetre) apart, being made 
 to rest on the diaphragm of the eye-piece, or placed in 
 front of the field lens in Ramsden's pattern. Previous to 
 using this form of micrometer the value of the sides of 
 these squares, with each objective, will have to be deter- 
 mined ; this is done in the following manner : Place a 
 stage- micrometer, ruled to hundredths and thousandths of 
 an inch (or tenths and hundredths of a millimetre), in posi- 
 tion upon the stage, and view it with the eye-piece having 
 the ruled circle in situ. The lines upon both micrometers 
 must now be rendered parallel, and carefully observed 
 where the one overlaps the other, and if any uneven 
 divisions appear, it will be better to pull out the draw- 
 tube until they become even, keeping a record as to how 
 much the tube has been withdrawn. As an instance 
 when using the i-inch objective and an A eye-piece, 
 each -j-Fff of an inch of the stage micrometer nearly 
 coincided with ten divisions of the ruled glass circle. In 
 order to make the coincidence exact, the draw-tube was 
 pulled out -nr of an inch ; therefore, for that objective and 
 ocular, each division of the eye-piece micrometer represents 
 -r^j- of an inch, when the draw-tube is extended the 
 same amount. 
 
 Jackson's eye-piece micrometer is shown in Figs. 202 
 
EYE-PIECE MICROMETERS. 
 
 233 
 
 and 203, inserted into the ordinary Huyghenian eye-piece. 
 The micrometer itself consists of a series of lines ruled 
 upon glass and set in a frame so that it may be moved 
 forward by a small screw, a spring at the extreme end 
 keeping it always in contact with it. The slits which are 
 cut in each side of the eye-piece 
 should be provided with a small 
 sliding tube to prevent dust 
 entering between the glasses. 
 
 The method of finding the 
 permanent values of the di- 
 visions of this micrometer is 
 identical with that previously 
 described, and when once found with accuracy should be 
 entered in the observer's note-book for future reference. 
 
 FIG. 202. 
 
 
 FIG. 203. 
 
 Ramsden's screw micrometer, the last we need mention, 
 is shown in Fig. 204. It is composed of a positive eye- 
 piece (see page 42), before which is stretched two very fine 
 parallel wires, one of which can be separated from the 
 other by a screw having one hundred threads to the inch, 
 the head being further graduated into one hundred parts, 
 as shown in the figure representing the instrument made 
 by Mr. Swift. 
 
 The field of view is illustrated by Fig. 205, and shows 
 clearly the lower portion, consisting of a thin plate of 
 brass, the edge being indented with a series of notches ; 
 every fifth indentation is deeper than the others, thus 
 facilitating the counting. Each notch is equivalent to one 
 
234 
 
 PRACTICAL MICROSCOPY. 
 
 turn of the milled head, so that the number of revolutions 
 may be read off without taking the eye from the object. 
 
 FIG. 204. 
 
 Quekett, in his 'Practical Treatise on the Use of the 
 Microscope,' has shown the theoretical possibility of measur- 
 ing a space so small as the one eight hundred thousandth 
 
 of an inch with the 
 eighth objective and 
 this micrometer ; but 
 there are many practi- 
 cal difficulties in the 
 way of attaining to this. 
 MEASUREMENT OF 
 ANGULAR APER- 
 TURE. Under the 
 head of microscopic 
 FIG. 205. measurements may be 
 
 described the method of using Prof. Abbe's apertometer 
 for measuring the aperture of objectives, a rough method 
 of accomplishing this having been already described on 
 page 56. An illustration of this instrument may be seen in 
 Fig. 206. It is a semicircular disc of crown glass, 3 5 inches 
 in diameter, and half an inch in thickness, polished on the 
 cylindrical edge and ground to an angle of 45 upon the 
 
PROFESSOR ABBE'S APERTOMETER. 235 
 
 diametrical edge. The centre of the semicircle is formed 
 by a small hole in a silvered cover a, cemented to the upper 
 face of the disc. Two indices of blackened brass Z>, b y sliding 
 on the periphery of the disc, afford visible marks for ob- 
 serving the aperture of any objective. On the upper face 
 of the disc there are two engraved scales, the outer indi- 
 cating the numerical aperture by direct observation. 
 
 FIG. 206. 
 
 In order to measure the aperture of any objective the 
 apertometer is placed upon the stage of a microscope, and 
 the objective, the aperture of which is to be measured, 
 roughly focussed to the small hole a, in the silvered cover. 
 In the case of an immersion lens, a drop of immersion fluid 
 must of course be applied. This done, the eye-piece of the 
 microscope is removed and the eye placed to the open 
 tube, the two indices of blackened brass b, b, being moved 
 to and fro until the points just touch the margins of the 
 illuminated field. The position of the indices is then 
 read off on the outer circle of figures, and half the sum of 
 both these readings will give the aperture of the objective. 
 
 For lenses of higher power than the J-inch, a 2-inch 
 objective is provided. This is made to screw into the 
 lower end of the draw-tube and used with an ordinary A 
 
2 3 6 
 
 PRACTICAL MICROSCOPY. 
 
 eye-piece, the whole being moved up and down until the 
 edge of the disc is seen quite distinctly ; the procedure is 
 then the same as with low powers. This auxiliary objec- 
 tive must be furnished with a diaphragm to cut off all false 
 rays, the aperture being one-eighth of an inch in diameter, 
 and situated i 5 inches from the achromatic combination. 
 
 The numerical aperture divided by the refractive index 
 of the medium in which it is measured produces the sine 
 of the semi-angle, and thus the angle in any medium may 
 be easily obtained. 
 
 The following table of natural sines may be of use in 
 this direction : 
 
 NATURAL SINES. 
 
 Degrees. 
 
 Sines. 
 
 Degrees. 
 
 Sines. 
 
 Degrees. 
 
 Sines. 
 
 I 
 
 0175 
 
 31 
 
 5150 
 
 61 
 
 8746 
 
 2 
 
 0349 
 
 32 
 
 5299 
 
 62 
 
 8829 
 
 3 
 
 0524 
 
 33 
 
 5446 
 
 63 
 
 8910 
 
 4 
 
 0698 
 
 34 
 
 '5592 
 
 64 
 
 8988 
 
 
 0872 
 
 
 5736 
 
 
 9063 
 
 6 
 
 I04S 
 
 36 
 
 5878 
 
 66 
 
 9135 
 
 7 
 
 1219 
 
 37 
 
 6018 
 
 67 
 
 9205 
 
 8 
 
 139* 
 
 38 
 
 ' 6l 57 
 
 68 
 
 9272 
 
 9 
 
 
 39 
 
 6293 
 
 69 
 
 9336 
 
 10 
 
 1736 
 
 40 
 
 6428 
 
 70 
 
 '9397 
 
 ii 
 
 1908 
 
 
 6561 
 
 
 '9455 
 
 12 
 
 2079 
 
 42 
 
 6691 
 
 72 
 
 '95 11 
 
 13 
 
 2249 
 
 43. 
 
 6820 
 
 73 
 
 9563 
 
 H 
 
 2419 
 
 44 
 
 6947 
 
 74 
 
 9613 
 
 51 
 
 2588 
 2756 
 
 45 
 46 
 
 7071 
 
 M 
 
 9659 
 9703 
 
 17 
 
 2924 
 
 47 
 
 ;73H 
 
 77 
 
 '9744 
 
 18 
 
 3090 
 
 48 
 
 
 78 
 
 978i 
 
 19 
 
 20 
 
 3256 
 3420 
 
 49 
 50 
 
 '7547 
 7660 
 
 g 
 
 9816 
 9848 
 
 21 
 
 3584 
 
 5i 
 
 7771 
 
 81 
 
 9877 
 
 22 
 
 3746 
 
 52 
 
 7880 
 
 82 
 
 9903 
 
 23 
 
 3907 
 
 53 
 
 7986 
 
 83 
 
 9925 
 
 2 4 
 
 4067 
 
 54 
 
 8090 
 
 84 
 
 "9945 
 
 
 4226 
 
 
 8191 
 
 85 
 
 9962 
 
 26 
 
 4384 
 
 56 
 
 8290 
 
 86 
 
 9976 
 
 27 
 
 4540 
 
 57 
 
 8387 
 
 87 
 
 9986 
 
 28 
 
 4695 
 
 58 
 
 8480 
 
 88 
 
 '9994 
 
 29 
 
 4848 
 
 59 
 
 8572 
 
 89 
 
 9998 
 
 30 
 
 5000 
 
 60 
 
 8660 
 
 90 
 
 I'OOOO 
 
USE OF THE APERTOMETER. 237 
 
 Abbe's apertometer is one of the instruments which may 
 be profitably purchased by the executive of every micro- 
 scopical society, for use ia testing the apertures of the 
 members' objectives. Such a proceeding would often save 
 the individual member much annoyance, and he would 
 then be certain of what he was purchasing. A case of this 
 kind has just fallen under the author's notice. A \ 
 objective was obtained of professedly 140 air angle, 
 and 8/. icxr. paid for it, while, when it came to be accu- 
 rately measured, it turned out only 108, and such a one 
 could have been bought for 50^. It should be the duty of 
 the executive of every microscopical society to secure its 
 members against fraud, and the method above stated 
 would most assuredly do this. 
 
CHAPTER X. 
 
 THE POLARISCOPE. 
 
 WHEN a ray of light is made to pass in a certain direction 
 through a crystal of Iceland spar, it becomes split up into 
 two portions of equal intensity, an ordinary ray and an 
 extraordinary ray respectively. If a ray, having undergone 
 ordinary refraction through a crystal of Iceland spar, be 
 allowed to pass through a second crystal, it is split up in 
 the same manner ; but the ordinary and extraordinary rays 
 will be of different degrees of intensity. When the second 
 crystal is rotated until the two are in similar or opposite 
 positions, then the ordinary ray appears at its greatest inten- 
 sity, while the extraordinary ray disappears. If the second 
 crystal is further rotated the extraordinary ray reappears 
 and increases in intensity as the rotation proceeds, while 
 the ordinary ray diminishes in intensity until the principal 
 planes of the crystals are at right angles to each other, 
 when the ordinary ray vanishes and the extraordinary ray 
 appears at its greatest intensity. 
 
 These and similar phenomena are called polarisation, 
 and two prisms are required to render it patent the 
 first for polarising the light, called the " polariser," or the 
 <' polarising prism ;" and the second, necessary for exhibit- 
 ing the fact that the light has undergone modification, 
 called the " analysing prism," or simply the " analyser." 
 
 There are several methods of producing the polarisation 
 of light, but the one usually employed for microscopical 
 purposes is by the aid of the Nicol or single image prism, 
 which yields a beam perfectly colourless, polarising com- 
 
THE NICOL PRISM. 
 
 239 
 
 pletely, and transmitting but one of the rays, the other 
 being entirely suppressed. 
 
 The Nicol prism is made from a rhombohedron of 
 Iceland spar, bisected in the plane which passes through 
 its obtuse angles, as shown in Fig. 207 by the letters 
 A B C D, the halves being joined again in the same order 
 by means of Canada balsam. 
 
 FIG. 207. 
 
 FIG. 208. 
 
 When a luminous ray enters this prism the ordinary ray 
 undergoes total reflection, passing out of the crystal at O, 
 while the extraordinary ray emerges at E, Fig. 208. 
 
 As attached to ordinary microscopes both polariser and 
 analyser are formed of Nicol prisms ; the former being 
 made to fix underneath the stage or into the sub-stage. 
 For this purpose it is mounted as 
 shown in C (Fig. 209), so that the 
 prism may be easily rotated by 
 means of the milled head. 
 
 The analyser may be used in 
 several ways. In the first, the 
 Nicol prism is set in a mount 
 screwing into the lower end of 
 the microscope body, just above 
 the objective, or in a brass box 
 sliding into the side of the tube, 
 in a similar manner to the Wen- 
 ham prism of a binocular instrument. In another, the 
 prism fits over the eye-piece in the place of the ordinary 
 
240 PRACTICAL MICROSCOPY. 
 
 cap, each kind of apparatus being shown in Fig. 209, 
 where the eye-piece analyser is shown at B, the other 
 form at A. 
 
 Sometimes a simple rhomb of Iceland spar, called also a 
 " double image prism," is used as an analyser, but is not so 
 generally useful as the Nicol prism previously described, 
 though a series of interesting experiments may be made 
 with it. 
 
 There are several other methods of polarising light : By 
 means of the bundle of glass polariser, the plate of black 
 glass, the tourmaline plate, and the sulphate of iodo- 
 quinine crystal ; but as all these can be seen in almost any 
 treatise on optics, it seems scarcely necessary to more than 
 mention them here. 
 
 The tourmaline plate may, perhaps, receive notice; in 
 this crystal the optical axis coincides with the axis of the 
 prism, and for optical purposes a plate is cut from it in a 
 plane parallel to this axis. There are many objections to 
 the use of a tourmaline plate, the principal being that a 
 considerable thickness is required, as unless the ordinary 
 ray is completely absorbed, the emergent light will be only 
 partially polarised, and this requisite thickness produces a 
 very undesirable colour. 
 
 When the analysing prism is placed immediately above 
 the objective it stops a considerable amount of light, 
 though it gives a full field, while when placed over the 
 eye-piece a smaller field but brighter image is obtained. 
 
 It is often useful to produce certain colour effects when 
 working with polarised light, and with this end in view a 
 plate of selenite is interposed between the polariser and 
 the object. Films of varying thicknesses are used ; they 
 are mounted in various ways, as selenite stages, object- 
 carriers, and the like. Perhaps the best form of selenite 
 stage is that made by Mr. Swift; it is shown in Fig. 210; 
 
SELENITE FILMS. 
 
 241 
 
 the reader will be able to make out its construction from 
 the illustration. 
 
 Mr. Swift's complete condenser, which has been already 
 shown at Fig. 44, is also fitted with selenite discs for colour 
 
 FIG. 210. 
 
 development, and also with a revolving film of mica, by 
 the combinations of which a very great number of tints 
 may be obtained. 
 
 Barker's selenite discs, as made by Messrs. Beck, are 
 shown in Fig. 211, and are very useful, seeing that one or 
 all of them can be put in and out of use in a moment. 
 
 FIG. 2ii. FIG. 212. 
 
 This form has been modified by Mr. Richards, who read a 
 paper upon "A New Method of using Barker's Films" 
 before the Royal Microscopical Society, March 9th, 1870. 
 
 R 
 
242 PRACTICAL MICROSCOPY. 
 
 His improved apparatus may be seen in Fig. 212, having 
 been reduced from the drawing which appeared in the 
 ' Monthly Microscopical Journal/ 
 
 The real advantage of the apparatus (if any) seems to 
 be in the application of gearing to produce revolution of 
 the films, an operation easily performed by the fingers 
 alone in the Ross instrument, as well as those of other 
 makers. 
 
 The colours produced by the selenite films are brought 
 about by variations in their thickness, the red being 
 yielded by the thickest, violet by the thinnest ; these films 
 vary between "00124 and *oi8i8 of an inch. The arrow- 
 head and letters PA indicate the positive axis of the 
 selenite, while the figures , f , and f denote the parts of a 
 vibration retarded by each disc. 
 
 But the student need not go to much expense over these 
 elaborate stages. They are intended to save time and not 
 money, and the ordinary plain mounted selenite films on a 
 3x1 inch glass slide will answer many purposes, though 
 incapable of rotation. If the red and green, blue and 
 yellow slides be provided, with a film of mica, this is about 
 all the student need purchase, at all events for some time 
 to come. 
 
 Rock crystal or quartz possesses the extraordinary 
 power called rotatory polarisation. If a ray of homo- 
 geneous light be polarised, and the analyser turned so that 
 it appears totally extinguished, the ray can be made to 
 pass again through the analyser by placing a thin section 
 of quartz, with its plane at right angles to the rays, 
 between the polariser and analyser. In order to effect 
 this the quartz crystal must be cut at right angles to its 
 axis. 
 
 In most petrological microscopes of the present day 
 Klein's plate of quartz is inserted in a movable box placed 
 
STARCHES UNDER POLARISED LIGHT. 
 
 243 
 
 immediately above the objective. This plate is usually 
 3 '75 millimetres in thickness, and is of the greatest utility 
 when very feeble doubly refracting crystals are being 
 examined, and in many other instances where it is sus- 
 pected that isotropic particles exist in admixture with 
 amorphous matter of a doubtful character. 
 
 The action of two Nicol prisms with an interposed plate 
 of quartz upon a beam of light has been made use of for 
 the purpose of registering the position of absorption bands 
 in the spectra of various substances ; but this properly 
 belongs to the next chapter. 
 
 The development of the study of objects by the aid of 
 polarised light may in the end bring about important dis- 
 coveries, and therefore should be studied more carefully 
 than it is at present. 
 
 Let the student examine some potato starch by the use 
 of ordinary light, and after noticing the position of the 
 hilum, again examine 
 with polarised light, 
 when he will not fail 
 to notice the black 
 cross, as shown in 
 Fig. 213. 
 
 For the observation 
 of starches under po- 
 larised light, they 
 should be mounted 
 in gum dammar dis- 
 solved in benzol as 
 in aqueous fluids the 
 effect is not developed 
 in so marked a manner. Wheat starch, which only faintly 
 shows the cross when observed in water, exhibits it very 
 plainly in gum dammar and benzol. The effects of polarised 
 
 R 2 
 
 FIG. 213. 
 
244 PRACTICAL MICROSCOPY. 
 
 light on the various starches maybe seen in Fig. 145. The 
 palates of molluscs are displayed remarkably well under 
 the influence of polarised light, especially when mounted in 
 gum dammar or Canada balsam. 
 
 A very common object, seen in almost all collections of 
 slides, is the section of rhinoceros horn. When examined 
 by ordinary light it appears to resemble a bundle of hairs ; 
 but when viewed with the polariscope, each cylindrical 
 aggregation is marked by a cross, bearing a striking resem- 
 blance to the starch granules illustrated by Fig. 213. 
 
 The muscular system of many minute animals can only 
 be satisfactorily made out by means of polarised light, 
 which very strikingly differentiates the tissues ; while such 
 objects as silk, cotton, flax, and jute are often to be distin- 
 guished from other substances by its aid. 
 
 But by far the most important application of the micro- 
 scope and polariscope is in relation to petrology, whereby 
 much regarding the nature of most minerals may be satis- 
 factorily made out. With this end in view several petro- 
 logical microscopes have been produced during the past 
 few years, notably from the houses of Mr. Watson and 
 Messrs. Swift and Son, the latter making the instrument 
 shown in Fig. 214. 
 
 This instrument is specially designed for the examination 
 of rocks and mineral substances, being furnished with a 
 concentric and revolving glass stage, self-centering arrange- 
 ment, goniometer, and complete polariscope. The polarising 
 prism is also provided with a divided circle and spring catch 
 to indicate when the Nicols are crossed ; it is made to slide 
 up in its fitting close to the under side of the object, and 
 on it are fitted condensing lenses of extreme high angle for 
 showing the brushes in crystals. When not required, the 
 polariser can be moved aside, entirely clear of the stage of 
 the microscope. The analyser is made to slide in the 
 
FIG. 214. 
 
246 PRACTICAL MICROSCOPY. 
 
 optical tube, immediately under which, in the same way, 
 is fitted a Klein's quartz plate. An extra analysing prism 
 with divided circle is placed over the eye-piece, and a con- 
 trivance for rotating crystals between it and the prism is 
 also added. The eye-piece has spider lines accurately 
 adjusted to the plane of the prism. 
 
 When the Nicol prisms (polariser and analyser) are set 
 at right angles to each other they are said to be crossed, 
 and there is a total extinction of light passing to the eye of 
 the observer; a thin section of an amorphous substance, 
 such as glass, if placed upon the stage, does not produce 
 any change, neither does a similar slice of any mineral 
 which crystallises in the cubic system ; and if the field 
 remains perfectly dark when an object is observed between 
 crossed " Nicols," it may be safely inferred that it belongs 
 to one of these classes, or happens to be lying in a plane 
 yielding single refraction only. 
 
 Some crystals appear not to polarise until the stage upon 
 which the slide is laid be rotated, and if it becomes visible 
 by this treatment it is certain the crystal does not belong 
 to the cubic system. 
 
 Minerals of all the other systems of crystallography 
 behave in various manners under crossed Nicols, and this 
 branch of study may be easily carried out with the aid of 
 the information to be found in Chapter VIII. Sections 
 should be cut in various planes of the crystal so as to 
 represent the principal directions of vibration and also the 
 axes of elasticity; but as this properly belongs to the 
 science of petrology, the student should refer to those 
 treatises in which these questions are specially considered. 
 
 In the petrological microscope shown by Fig. 214 there 
 is fitted an arrangement for showing the rings in biaxial 
 crystals : a crystal of augite spar (diopside) is brought into 
 the field of the microscope, and its entire system of rings 
 
USE OF DOUBLE-IMAGE PRISM. 247 
 
 may be exhibited as large, and with as much brilliancy, as 
 in Norremberg's polariscope. 
 
 These coloured rings form a curious study ; when, for 
 instance, a section of Iceland spar (a negative uniaxial 
 crystal) is cut from I to 20 millimetres thick in a plane 
 perpendicular to the axis, and observed with polarised light, 
 the following curious appearances are presented. First, 
 when the axes of both polariser and analyser are perpen- 
 dicular, there is shown a beautiful series of coloured rings 
 traversed by a black cross ; and secondly, when the axes 
 are parallel, the coloured rings possess complementary tints 
 to those shown at first, while a white cross has taken the 
 place of the black one. 
 
 In biaxial crystals the system of rings is more complicated, 
 and this series may be well studied in a plate of nitrate of 
 potash, cut perpendicularly to its axis. 
 
 In order to exhibit the phenomenon of double refraction 
 a " double-image prism " is used over the eye-piece, in con- 
 junction with an objective; a plate of brass, pierced with a 
 series of holes T V to \ of an inch in diameter, being laid 
 upon the stage. When the polariser is fitted into its place 
 below the stage, and the double-image prism over the eye- 
 piece, there will appear (in some positions) two images, 
 while when the prism is moved, one of the images will be 
 completely obliterated, a change taking place at every 
 quarter of a revolution. When the polariser is taken 
 away the eye-piece shows two distinct images of the 
 light circle, the ordinary and the extraordinary ray, which 
 describe a circle upon revolving the eye-piece. If one 
 of the larger apertures be now placed under the objective 
 the images will not be completely separated but will overlap. 
 
 These are only a few of the many curious effects produced 
 by polarised light, and its study should be more fostered 
 and encouraged. 
 
248 
 
 PRACTICAL MICROSCOPY. 
 
 It is not enough to mount slides of salicine and other 
 crystalline forms for the production of rainbow colours, 
 and therefore the author imagines he cannot do better 
 than give a list of the principal works which may be con- 
 sulted: * Lectures on Polarised Light,' by T. P., Long- 
 man and Co., 1843; 'Polarisation of Light/ by William 
 Spottiswoode, Nature Series, 1874 ; 'A Familiar Intro- 
 duction to the Study of Polarised Light/ by C. Woodward, 
 Van Voorst, 1861 ; 'Mineralogie Micrographique/ MM. 
 Fouqud and LeVy, published by the French Minister of 
 Public Works, and is a most valuable work to all concerned 
 in microscopic mineralogy. 
 
 To conclude this chapter a list is given of many polaris- 
 ing objects : 
 
 ANIMAL SUBSTANCES. 
 
 Palate of limpet. 
 
 periwinkle. 
 
 whelk. 
 Embryo oysters. 
 Human hair. 
 Raw silk. 
 
 Human corns. 
 Horn of rhinoceros. 
 
 antelope. 
 Skin of rhinoceros. 
 Alpaca wool. 
 Porcupine quill.- 
 
 VEGETABLE SUBSTANCES. 
 
 Starch from tous les mois. 
 potato. 
 
 ,, arrowroot. 
 maize. 
 Cotton fibres. 
 
 Plant raphides. 
 
 Seed of Eccremocarpus. 
 
 Cuticle of Correa cardinalis. 
 
 Fern scales. 
 
 Jute fibres. 
 
 CHEMICAL CRYSTALS. 
 
 Salicine. 
 
 Quinine. 
 
 Chlorate of potash. 
 
 Cane sugar. 
 
 Brownian motion in fluids. 
 
 Oxalic acid. 
 
 Sulphate of copper. 
 
 Asparagine. 
 Quinidine. 
 Strychnine. 
 Tartaric acid. 
 Citric acid. 
 Sulphate of lime. 
 Chloride of barium. 
 
CHAPTER XL 
 
 THE MICRO-SPECTROSCOPE. 
 
 THE micro-spectroscope is used as a means for exhibiting 
 the absence of certain rays of light in a beam which has 
 been modified by its passage through certain substances or 
 solutions. Generally speaking there are two patterns of 
 the instrument, the former made by Messrs. Beck, as 
 shown in Fig. 215, and that 
 made by Mr. Browning, 
 shown in Fig. 216. There 
 is not much difference be- 
 tween the two in actual 
 working, the form the 
 author prefers, however, 
 being that of Mr. Browning. 
 
 The Sorby - Browning 
 instrument consists of a 
 series of prisms, of crown 
 glass and flint, mounted 
 in a small tube, so that 
 they can be removed at 
 pleasure. Immediately be- 
 low this tube is an achro- 
 matic eye-glass ; and below the adjustable slit, placed about 
 the centre of the widened part of the tube, is an ordinary 
 plano-convex field-lens. 
 
 The amount of dispersion, that is, the length of the 
 visible spectrum, is produced by alterations in the prisms, 
 and it is as well for the worker in this branch of micro- 
 
 FIG. 215. 
 
250 
 
 PRACTICAL MICROSCOPY. 
 
 scopy to be provided with several copies of the tube, 
 containing prisms yielding different degrees of dispersion. 
 Mr. Browning has made for the author four such tubes, 
 producing a small, medium, and large amount of dispersion, 
 one of which can easily be substituted for the other. 
 
 FIG. 216. 
 
 The student must remember that an increased dis- 
 persion does not define the absorption bands any the 
 better ; on the contrary, fine and delicate lines, easily 
 seen by the use of a prism with moderate dispersion, are 
 often lost when one of large dispersion is substituted. 
 
 To use this instrument, insert it as an eye-piece in the 
 microscope, screw on the object-glass, and place the object, 
 the spectrum of which is required, upon the stage. Illu- 
 minate by means of the sub-stage mirror if the object is 
 transparent, or with mirror, Lieberkuhn, or side-reflector if 
 opaque. Remove the tube A, and open the slit by means 
 
MR. SORBY'S CELLS. 251 
 
 of the milled head H. Focus the object and then gradu- 
 ally close the slit till a good spectrum is obtained, and 
 this may be further improved by throwing the object a 
 little out of focus. Each portion of the spectrum differs a 
 little from adjacent parts in refrangibility, and delicate 
 bands or lines can only be brought out by focussing their 
 own parts of the spectrum, which may be done by means 
 of the milled head B. 
 
 One advantage which the micro-spectroscope possesses 
 is that extremely small quantities may serve for observa- 
 tion, and for this purpose powers varying from ^-inch to 
 ^o-inch may be used. 
 
 It is very easy to have the tints of the solutions ex- 
 amined too intense, so that nothing but a general and 
 indefinite absorption appears throughout the entire spec- 
 trum. Nothing, perhaps, can show this better than a 
 solution of permanganate of potash or Condy's pink 
 fluid. 
 
 Mr. Sorby has devised what he has termed a wedge cell, 
 in which to view the liquid for its absorption ; it is shown 
 in Fig. 217. By this means an increasing thickness of fluid 
 and consequent intensity of colour can be brought under 
 observation with the minimum of trouble. Again, very 
 
 FIG- 217. FIG. 218. 
 
 minute quantities of solutions may be examined in the 
 slide shown in Fig. 2 1 8, made of a piece of barometer tube 
 cut and ground evenly, and then cemented to a piece of 
 ordinary glass. 
 
 Mineral sections, crystals, blowpipe-beads, &c., should 
 
252 PRACTICAL MICROSCOPY. 
 
 invariably have a small cardboard diaphragm, one-eighth 
 diameter, placed beneath them ; the spectrum is then 
 much better defined. With a slide containing a mass of 
 small crystals the object need merely be thrown a little 
 out of focus. 
 
 When observing the spectra of liquids in experiment 
 cells, or through small test-tubes, always slip over the 
 i or 2-inch objective a cap with a hole T V of an inch dia- 
 meter. Slide this cap just sufficiently to bring the small 
 hole a little within the focus of the objective. By this 
 arrangement all extraneous light is prevented from passing 
 up the body of the microscope, except what passes through 
 the object. Unless this precaution be attended to, a false 
 result is sometimes obtained. 
 
 Substances which give bands or lines in the red are 
 best seen by gaslight, while those which give bands in the 
 blue are brought out far better by daylight. Such a 
 specimen as oxalate of chromium and soda is almost 
 opaque by daylight, showing no bands, though when ex- 
 amined by a lamp the spectrum exhibits three beautifully 
 fine lines in the red, two of which are exceedingly delicate. 
 Again, uranic acetate can only be seen to advantage by 
 strong daylight, since the band in the violet would be 
 invisible by lamplight. 
 
 In solids, as crystallised uranic acetate, the tubes should 
 be laid over a piece of black velvet on the stage of the 
 microscope and illuminated with a bull's-eye condenser or 
 side reflector. 
 
 It may be at first thought that absorption in the spec- 
 trum is due to the particular colour only that is to say, 
 a blue would always act as the ammoniacal sulphate of 
 copper ; a brown, as Parisite ; a green as chlorophyll ; and 
 all reds would absorb the same light from the spectrum as 
 a film of blood ; but a few experiments would soon show 
 
SPECTRA OF VARIOUS SUBSTANCES. 
 
 253 
 
 that this is by no means the case, and a reference to 
 Fig. 219 will show this clearly. 
 
 In the illustration, A represents the absorption spectrum 
 of oxalate of didymium viewed by reflected light. The 
 oxalate is a white powder, yet the six bands are very 
 plainly defined even with ordinary instruments, while with 
 a good set of prisms the broad band at the red end of the 
 spectrum may be resolved into several dark lines. 
 
 RED 
 
 .VIOLET 
 
 FIG. 219. 
 
 The absorption bands of didymium were first described 
 in 1858 by Dr. J. H. Gladstone, and are remarkable for 
 their extreme sharpness. 
 
 At B is shown the spectrum of the deep blue solution 
 
254 PRACTICAL MICROSCOPY. 
 
 of ammonio-sulphate of copper, already alluded to as 
 being used for purposes of photomicrography, and the 
 figure here shows us how completely the red end of the 
 spectrum is cut off, and how little of the actinic portion is 
 absorbed. C is given to show how mixtures of substances 
 may be detected ; the illustration represents the absorption 
 bands of Parisite a brown and somewhat rare mineral 
 from the emerald mines of New Granada. It consists 
 principally of the carbonates of cerium, lanthanium, and 
 didymium, the spectrum of the last showing out with its 
 usual distinctness. At D may be seen the spectrum pro- 
 duced by a colouring matter obtained from the wing 
 feathers of the Cape lory (Turacus albocristatus) by Pro- 
 fessor Church, and to which he has given the name 
 "turacine." E shows the spectrum (or one of them) of 
 chlorophyll, and is characterised by the deep broad band 
 in the red end of the spectrum ; K, the orange colouring 
 matter obtained from aphides by Mr. Sorby, remarkable 
 on account of the band in the yellow. F, G, H, and I form 
 a series ; they are the spectra of blood and its modifications. 
 F is fresh blood ; G deoxidised blood ; H blood treated 
 with citric acid ; while I is similar to H but deoxidised. 
 
 Mr. Sorby published an important paper on this subject 
 in vol. vi. of the * Monthly Microscopical Journal/ Fresh 
 blood gives two dark bands in the green part of the 
 spectrum, as is shown at F. This colouring matter is 
 haemoglobin, and the series of changes produced by several 
 reagents may be observed there. A small quantity of 
 fresh blood diluted with a little water should be inserted 
 in the tube shown in Fig. 218, and, examined upon the 
 stage of the microscope, the two bands in the green will be 
 plainly perceived. Next add a trace of ammonia, a small 
 quantity of Rochelle salt (double tartrate of potash and 
 soda), and a particle of the protosulphate of iron and 
 
QUARTZ SCALE. 255 
 
 ammonia (ferrous amm. sulphate), and examine again. The 
 two bands will gradually fade and be replaced by a fainter, 
 though broad and single, band, as shown in G. If this be 
 allowed to oxidise in the air, the two original bands of 
 haemoglobin can be seen again, and on adding a little citric 
 acid the spectrum becomes changed to that seen in H. 
 The citric acid has changed the haemoglobin into haematin, 
 and this latter can be further deoxidised by contact with 
 ferrous sulphate, when it produces the spectrum shown at I. 
 . Other spectroscopic changes can be induced in blood, but 
 for these we must refer the reader to the tenth Report of the 
 medical officer of the Privy Council, 1867. 
 
 In all work such as this, it is advantageous to be able to 
 throw up a second spectrum alongside the first for com- 
 parison; and in all good instruments this is provided for 
 by fixing a small prism across half the slit, which receives 
 its light from the side of the tube, dispersing it upwards to 
 the eye. 
 
 For registering the position of the absorption bands 
 two methods have been devised, (i) the quartz scale of 
 Mr. Sorby, and (2) the bright spot micrometer of Mr. 
 Browning. The first is constructed of two Nicol prisms, 
 with an interposed plate of quartz, about "043 of an inch 
 in thickness, cut parallel to the principal axis of the crystal. 
 This produces twelve interference lines or black bands in the 
 spectrum, and is adjusted so that the sodium line of the 
 solar spectrum is exactly midway between the third and 
 fourth band, reckoning from the red end. This adjustment 
 is performed by varying the thickness of the quartz plate, 
 by no means an easy operation, as a very slight difference 
 in thickness upsets the scale completely. 
 
 The Sorby quartz scale is small and convenient, and is 
 shown at Fig. 220. 
 
 The use of this scale monopolises one of the two spectra, 
 
256 
 
 PRACTICAL MICROSCOPY. 
 
 FIG. 220. 
 
 so that in many cases Mr. Browning's bright spot micro- 
 meter is decidedly preferable, as it does not preclude the 
 use of either. The lateral piece AA 
 is attached to the upper part of the 
 prism tube, as shown in Fig. 221. At 
 its outer extremity is an oblong box 
 containing a glass plate, upon which 
 is photographed a minute biconvex 
 spot bright on a dark ground. This 
 
 is moved vertically by means of a screw connected with 
 the graduated head M, the spot is illuminated by the small 
 
 plane metallic mirror R, 
 and its image formed by 
 the lens C is capable of 
 being adjusted for focus 
 by the milled collar B. 
 This image is reflected to 
 the eye of the observer 
 from the face of the 
 upper prism, inclined at an 
 angle of 45, and is viewed 
 along with the two spectra 
 between which it appears 
 to pass when the milled 
 head M is turned. In 
 the construction of maps, 
 notice how many revolu- 
 tions of the milled head 
 M will carry the bright 
 _ f spot through the whole 
 
 length of the spectrum, 
 
 which will vary according to the dispersive power of the 
 prisms. 
 
MICRO-SPECTROSCOPIC MAPS. 257 
 
 A centimetre will be found a convenient measure to 
 represent one revolution: the millimetre will then equal 
 ten of the smallest divisions of the milled head, or T ^ of a 
 revolution; these smallest divisions, or thousandths, need 
 not be regarded, as without them the spectrum will be 
 divided with sufficient accuracy. Next measure the dis- 
 tances between the Frauenhofer lines. This should be done 
 with great care, as when once determined it will be constant. 
 The lines A and a need not be measured, as they are in 
 the dark part of the red, and are only to be seen in an 
 extremely bright light, so will hardly be required in prac- 
 tice. The same remark will apply to the line H. The 
 spectrum to be measured will therefore extend from about 
 B to a little beyond G. 
 
 Let this scale be drawn on cardboard and preserved for 
 reference. Now measure the position of the dark bands in 
 any absorption spectra, taking care for this purpose to use 
 lamplight, as daylight will give, of course, the Frauenhofer 
 lines, and tend to confuse the spectrum. If the few lines 
 occurring in most absorption spectra be now drawn to 
 the same scale as the solar spectrum, on placing the scales 
 side by side, a glance will show the exact position of the 
 bands in the spectrum relatively to the Frauenhofer lines, 
 which thus treated form a natural and unchangeable scale. 
 But for purposes of comparison it will be found sufficient to 
 compare the two lists of numbers representing the micro- 
 metric measures, simply exchanging copies of the scale 
 of Frauenhofer lines, or the numbers representing them 
 will enable observers at a distance from each other to com- 
 pare their results, or even to work simultaneously on the 
 same subject. 
 
 Owing to the sliding and other fittings between the 
 prisms and the slit, the micrometer cannot be depended on 
 for pointing to the position of a line by setting it to the 
 
 s 
 
2 5 8 
 
 PRACTICAL MICROSCOPY. 
 
 number recorded on the scale, but is only to be used for 
 measuring between lines, and for this purpose it may be 
 trusted. 
 
 Dr. Lawson has suggested that the great advantage of 
 this contrivance is that it does not monopolise one of the 
 two spectra, as with the use of the quartz scale; for in 
 describing two spectra, only slightly differing from each 
 other, it may be used at once to determine the difference 
 between them. 
 
 In concluding this chapter it may be as well to give a 
 short list of substances showing well-defined absorption 
 bands, such as may be of use to the student upon commenc- 
 ing to use the instrument. 
 
 Nitrate of didymium. 
 Oxalate of ,, 
 
 Oxide of (blowpipe- 
 
 bead). 
 Chloride of cobalt (in alcohol). 
 
 (in chloride of 
 
 calcium). 
 
 (a crystal). 
 
 Cobalt glass (blue). 
 Sulphate of uranium. 
 Acetate of .. 
 
 Oxalate of chromium and soda. 
 
 Sulphate of chromium. 
 
 Permanganate of potash. 
 
 Ruby glass (copper). 
 
 Ammonio-sulphate of copper. 
 
 The aniline colours. 
 
 The naphthalene colours. 
 
 Indigo sulphate. 
 
 Carmine. 
 
 Litmus (blue and red). 
 
 The colouring matters of plant petals. 
 
CHAPTER XII. 
 
 STAINING AND INJECTING. 
 
 IN many instances it is necessary to stain a preparation 
 not merely to form a pretty object let this be understood at 
 the outset ; but to show certain details of formation not 
 easily discerned in an unstained specimen. When aniline 
 blue and magenta are used for the double staining of 
 vegetable tissues, such as the section of a Burdock stem, 
 Mr. Barrett tells us the different parts are stained as 
 follows : 
 
 Pith ;. Very pale magenta. 
 
 Cellular tissue Deep magenta. 
 
 Spiral vessels of medullary sheath . . Deep blue. 
 
 Pitted vessels Blue. 
 
 Cambium Deep blue. 
 
 Liber cells Dark magenta. 
 
 Laticiferous vessels Deep blue. 
 
 Cuticle parenchyma . . Pale blue. 
 
 Epidermis Deep blue. 
 
 Hairs Pale magenta. 
 
 Mr. Stiles, in a paper to 'The Northern Microscopist,' 
 makes the following remarks upon this subject : 
 
 Stems of all kinds should, if possible, be cut when fresh. 
 If they cannot be obtained in this state, they may, previous 
 to cutting, be soaked in cold or tepid water, or in a mixture 
 of equal volumes of spirit of wine, glycerine, and water. 
 Fresh stems or roots can be preserved in this medium for 
 almost any length of time, and will remain in excellent 
 condition for the section machine. 
 
 Logwood Staining. Wood sections require bleaching 
 
 S 2 
 
260 PRACTICAL MICROSCOPY. 
 
 before being stained. The bleaching solution is made by 
 mixing \ oz. of chloride of lime with a pint of water, 
 shaking occasionally for an hour, and after allowing the 
 sediment to subside, decanting the clear solution. The 
 process of bleaching should be carefully watched and 
 stopped when complete. Tissues vary so much in colour 
 and density that no fixed time can be given for bleaching 
 them. Very thorough washing is necessary. The elimina- 
 tion of the chlorine will be much facilitated by placing the 
 sections, after removal from the bleaching liquid, in a solu- 
 tion of sulphite of soda (i drachm to 4 oz. of water) for an 
 hour, then washing the sections by soaking them for at least 
 six jor eight hours in water, changing occasionally, and 
 finishing with distilled water. If they are not to be stained 
 at once, they should be preserved in water containing 
 20 per cent, of alcohol, as when kept in water only, in the 
 course of two or three days they become covered with a 
 peculiar fungus growth. At this stage all air-bubbles 
 should be removed from the tissue. This is conveniently 
 done by placing the sections in dilute alcohol, putting them 
 under the receiver of an air-pump, Fig. 222, and exhausting 
 the latter, repeating the pumping occasionally so long as 
 air-bubbles are given off. For this purpose a small tube 
 bottle is employed about ij inch long, and a receiver just 
 large enough to hold it, the process being thus rendered a 
 rapid one. 
 
 Where it is required to uniformly stain the section in 
 order to render prominent the more delicate cell walls, 
 logwood answers exceedingly well and is very permanent. 
 
 LOGWOOD SOLUTION. 
 
 Logwood, in coarse powder . . 2 oz. 
 
 Distilled water 10 oz. 
 
 Boil for half an hour in a glass beaker, replacing what is 
 lost by evaporation ; strain, and to each ounce of liquid 
 
LOGWOOD STAINING. 
 
 26l 
 
 when cold add 60 grains of alum and one drachm of 
 alcohol, rub well together, filter through paper, and preserve 
 in a stoppered bottle. 
 
 FIG. 222. 
 
 STAINING PROCESS. Make a filtering cone by twice 
 folding a piece of filtering paper about i J inch diameter ; 
 support this in the neck of a small beaker or tube, and 
 filter through it about ten drops of the above liquid, add 
 thirty drops of distilled water, place the sections in the 
 mixture for five minutes (more or less), pour off the stain, 
 wash once or twice in distilled water, then soak for half an 
 hour in a solution of alum (20 grains to the ounce), remove 
 this, wash well with distilled water, and preserve in alcohol 
 so as to be ready for mounting. 
 
 The logwood solution prepared in this way gives more 
 satisfactory results than when made as usually recom- 
 
262 PRACTICAL MICROSCOPY. 
 
 mended from extract of logwood, the latter being a very 
 variable article. 
 
 For double staining, which is more generally useful than 
 the method just described, many formulae have been given, 
 the process having originated with Mr. G. D. Beatty, of 
 Baltimore, U. S. A. 
 
 Perhaps the best paper in this country upon the subject 
 is that which appeared in the pages of ' Science-Gossip/ 
 for January 1880; but even the process therein described 
 is in several points open to modification and improve- 
 ment. 
 
 Mr. A. J. Doherty, in a paper to ' The Northern Micro- 
 scopist/* describes at some length the method of staining in 
 carmine and green. The art consists of five stages or pro- 
 cesses i, decolorising the sections ; 2, washing the same ; 
 3, preparing for staining ; 4, staining in carmine ; 5, staining 
 in green. 
 
 After bleaching and thoroughly washing to eliminate all 
 the chemicals, as already described, in order to obtain deep 
 colours, the sections must be steeped in a mordant com- 
 posed of a 10 per cent, solution of alum and water for 
 twenty-four hours, at the end of which time they will be 
 ready to be placed in the first staining fluid, the formula 
 for which is as follows : 
 
 Carmine 15 grains. 
 
 Ammonia 15 grains. 
 
 Water 2 oz. 
 
 The carmine is to be dissolved in the ammonia over the 
 flame of a spirit-lamp, the water added next, and the fluid 
 filtered before it is used. 
 
 Immerse the sections in this stain for six or eight hours, 
 then take them out, and wash them in not more than two 
 
 * June 1881. 
 
PICRO-CARMINE STAINING. 263 
 
 changes of water, and finally transfer them to the green 
 stain, for which take 
 
 Aniline green 5 grains. 
 
 Absolute alcohol I oz. 
 
 Dissolve in a test tube, using a slight heat only, to avoid 
 any unpleasant mishap, and filter before using. After a 
 three hours' soaking in the above, the staining will be com- 
 pleted, and the sections should be mounted without delay, 
 after having washed the superfluous colour away with 
 methylated spirit. The method of mounting these will be 
 given later on. 
 
 Staining in Picro-carmine* Picro-carmine is the most 
 truly selective of any double stain yet employed. A 
 special modification of it is required for wood sections as 
 follows : 
 
 PICRO-CARMINE SOLUTION. 
 
 Carmine (finest) 2 grains. 
 
 Liquid ammonia (sp. gr. '960) .. .. \ drachm. 
 Distilled water I oz. 
 
 Put the carmine in a 2-ounce stoppered bottle, pour in the 
 liquid ammonia, and shake occasionally until dissolved, 
 then add the water. 
 
 Picric acid 8 grains. 
 
 Alcohol .. .. I oz. 
 
 Dissolve in a test-tube with a gentle heat, then mix with 
 the solution of carmine. 
 
 STAINING PROCESS. Place the sections in 50 per cent, 
 alcohol for one hour, then treat with the recently filtered 
 staining solution until the desired effect is produced (usually 
 from half to two or three hours), remove the dye, wash 
 quickly three or four times with alcohol 50 per cent., then 
 soak in an alcoholic solution of picrate of ammonia, 
 
 * Mr. M. H. Stiles in 'The Northern Microscopist,' July 1881. 
 
264 PRACTICAL MICROSCOPY. 
 
 changing this at the expiration of an hour, and allowing 
 the sections to remain in the second solution for about the 
 same period. 
 
 The logwood stained sections, after being well washed, 
 are soaked in alcohol for an hour, then removed to oil of 
 cajeput, and allowed to remain in this for a couple of 
 hours; at the end of this time transfer them to oil of 
 turpentine. In less than an hour they will be ready for 
 mounting in balsam or dammar. The sections should not 
 be allowed to remain long in the turpentine or else they 
 become brittle. 
 
 In the case of picro-carmine stained sections they should 
 be removed from the alcoholic solution of picrate of 
 ammonia into alcohol for about a minute, then into oil of 
 cajeput. 
 
 The object of employing an alcoholic solution of picrate 
 of ammonia is to avoid the loss of colour which attends the 
 use of alcohol only, the yellow stain of picric acid being 
 readily removed from the tissue by that liquid. Picrate of 
 ammonia may be easily made by adding a slight excess of 
 liquid ammonia to a solution of picric acid, and evaporating 
 the mixture to dryness at a gentle heat.* The residue is 
 dissolved in alcohol and filtered. 
 
 Wood sections stained in picro-carmine are very beauti- 
 ful and permanent. The staining being done at one 
 operation, and the colours being remarkably selective, 
 there is an absence of secondary tints, as in the case of 
 most other double stains, especially where one tint is 
 partially washed out to make way for another. 
 
 Regarding permanence, some stained sections mounted 
 nearly five years ago appear to have retained their 
 brilliancy unimpaired. 
 
 * This salt had better be purchased by the student, as the picrates explode 
 violently when over -heated. 
 
STAINING ANIMAL SECTIONS. 265 
 
 In place of alcohol, methylated spirit may be used if 
 desired. 
 
 The chromo-lithograph forming the frontispiece to this 
 work, illustrates very clearly the value of the foregoing 
 methods. The four outside figures are specimens of 
 double-staining in carmine and green, some of the admi- 
 rable specimens of Mr. Ward, of Manchester, while the 
 centre figure is a representation of the slide sent by Mr. 
 Stiles, of Doncaster, to illustrate his paper on picro-carmine 
 staining in 'The Northern Microscopist.' 
 
 Histological (animal) staining differs somewhat from the 
 foregoing, many processes having been devised to strikingly 
 differentiate the tissues. In 1876, Dr. Elizabeth Hoggan 
 described a process with iron and pyrogallic acid as 
 follows :* 
 
 " The colouring agents required are a one or two per cent, 
 solution of perchloride of iron in alcohol, and an alcoholic 
 solution of pyrogallic acid of similar strength." 
 
 The section or membrane to be stained is first treated 
 for a short time with alcohol, the iron solution filtered 
 upon it, and then poured off after a couple of minutes. 
 The pyrogallic solution is then filtered upon it, and 
 when the desired depth of staining has been obtained, 
 the tissue is washed and mounted in any of the usual 
 ways. 
 
 The nuclei and nucleoli are by this means coloured 
 black, and the cell-substance coloured more or less. A 
 bluish tint may be imparted by washing in alkaline water 
 or in water highly charged with carbonate of lime. 
 
 Osmic acid has been frequently recommended for 
 
 staining animal tissues black, but it is doubtful whether 
 
 anything is gained by its use. Dr. G. Brosicke, of Berlin, 
 
 advises a mixture of osmic and oxalic acids for this 
 
 * ' Journal of the Quekett Club,* iv. p. 180. 
 
266 PRACTICAL MICROSCOPY. 
 
 purpose. Thin sections of animal tissues are placed in a 
 one per cent, osmic acid solution, and then carefully 
 washed to remove all superfluous acid. They must then 
 be immersed for about twenty-four hours in a solution of 
 one part of oxalic acid to fifteen of water, when after 
 washing they are ready for examination. 
 
 The oxalic acid produces darker or lighter shades (carmine 
 and Burgundy tints) in proportion to the length of time 
 the section has been immersed in osmic acid, but if the 
 tissue has once become blackened, the oxalic solution is 
 powerless to redden it afterwards. 
 
 Chloride of gold solution has been employed for colour- 
 ing nerve-fibres ; a solution in water of one or two grains to 
 the ounce is generally used. The section should be soaked 
 in the solution until it has acquired a straw-coloured tinge, 
 it is then to be washed and placed in a one per cent, solu- 
 tion of acetic acid. In the light the nerve-fibres become 
 coloured a blue or violet tinge in a few hours. Nitrate of 
 silver is a very important agent for the staining of animal 
 tissues. Dr. Lionel Beale writes, " A weak solution may be 
 imbibed by delicate tubes, and part being precipitated in 
 the tube, perhaps as a chloride, or in combination with 
 some albuminous material, subsequently becomes decom- 
 posed by the action of light." 
 
 Recklinghausen, who has employed this plan with much 
 success, uses a very dilute solution, made by dissolving 
 one grain of nitrate of silver in from one to two ounces of 
 distilled water. 
 
 In 1863, Dr. Roberts, of Manchester, used a solution of 
 tannin and magenta for staining the red human blood- 
 corpuscles, and this is a subject which still requires 
 investigation. 
 
 Dr. Beale's carmine fluid for staining all forms of bioplasm 
 of living things is made as follows : 
 
DR. LIONEL BEALES BIOPLASM STAIN. 267 
 
 Carmine 10 grains. 
 
 Liquor ammonias drachm, 
 
 Glycerine 2 oz. 
 
 Distilled water 2 oz. 
 
 Alcohol ., .. | oz. 
 
 The carmine is to be dissolved in the ammonia, boiled 
 for a few seconds, and set aside for an hourj the glycerine, 
 water, and alcohol may then be added, and the whole 
 allowed to stand until thoroughly settled, when the clear 
 fluid is to be decanted and kept for use. Dr. Beale tells us 
 that if the solution be very alkaline, the colouring will be 
 too intense, and much of the soft tissue round the bioplasm 
 will be destroyed by the action of the ammonia ; if, on the 
 other hand, the solution is neutral, the uniform staining of 
 tissue and bioplasm may result. In some cases the fluid 
 must be diluted with alcohol, water, or glycerine, in order 
 to get the best results; and Dr. Beale observes that the 
 process should not be hastily condemned without trying 
 the effect of modifying the quantities of the various 
 constituents. 
 
 There are many other processes to be found scattered 
 through the pages of microscopical literature, but space 
 compels us to close the subject here. 
 
 The process of injecting should now claim our attention, 
 though it is feared that actual practice with the syringe 
 will be found of far more use than any written instructions 
 can ever be. 
 
 There are two methods of making injections, opaque and 
 transparent ; in the former the colouring matters, such as 
 vermilion, chromate of lead, white lead, or Prussian blue, 
 are well mixed with size made of gelatine, of such a 
 strength that it will form a firm jelly on cooling. To make 
 the size, soak one ounce of gelatine in a pint of water over- 
 night, and dissolve with heat in the morning. 
 
 The colouring matters must be mixed up in a mortar 
 
268 PRACTICAL MICROSCOPY. 
 
 with the size, poured into a tin vessel placed in hot water, 
 and strained through fine muslin into another, just before 
 it is required to be used. It must not be forgotten that 
 when size is used, the preparation to be injected must be 
 steeped in hot water, and kept warm until the operation is 
 finished. 
 
 Opaque injections in various colours often form very 
 instructive objects. An injection of the liver illustrates 
 this very well : the artery may be injected with vermilion, 
 the portal vein with white lead, the duct with Prussian 
 blue, and the hepatic vein with lake. A section of an 
 injected kidney, with Prussian blue and lake, is also a 
 pleasing slide when well performed. 
 
 After all, opaque injections have but a limited scientific 
 value, and therefore the student is advised to utilise his 
 energies upon the transparent class, as they can be 
 examined with all powers, and when preserved in fluids 
 the most delicate structures retain their integrity. 
 
 The Prussian blue fluid for transparent injections is 
 made as follows (Beale) : 
 
 Glycerine i oz. 
 
 Alcohol i oz. 
 
 Ferrocyanide of potassium 12 grains. 
 
 Tinct.ferriperchlor I drachm. 
 
 Water 407. 
 
 The ferrocyanide is to be dissolved in an ounce of the 
 water and the glycerine added, while the Tinct. ferriper- 
 chlor. is separately mixed with another ounce of the water. 
 These two solutions should now be mixed very gradually, 
 and well shaken, the iron being added to the ferrocyanide ; 
 the mixture of spirit with the remainder of the water must 
 now be added very gradually, when the fluid is ready for use. 
 
 Dr. Beale's carmine fluid is made in the following 
 manner : 
 
INJECTING. 269 
 
 Liq. ammonise 5 drops. 
 
 Carmine 5 grains. 
 
 Glycerine i oz. 
 
 Acetic acid 8 drops. 
 
 Glycerine I oz. 
 
 Alcohol 2 drachms. 
 
 Water 6 drachms. 
 
 Dissolve the carmine in a few drops of water, and the 
 liquor ammonise at a gentle heat, and when dissolved add 
 half an ounce of the glycerine. Shake well, and then add 
 gradually half an ounce of the glycerine in which the acetic 
 acid has been dissolved, well shaking the bottle between 
 each addition. If not decidedly acid to litmus paper, a 
 few more drops of acid must be mixed with the remainder 
 of the glycerine, and added as before. Lastly, add the 
 alcohol and water very gradually, well shaking until the 
 whole is well mixed. 
 
 The author does not intend to enter further into the 
 details of this branch of microscopy ; with the foregoing 
 solutions the student will be enabled to learn the elements 
 of the art, and if afterwards he has a desire to proceed 
 further, he will find full instructions for many fluids in ' Das 
 Mikroskop,' by Dr. Frey, or in the admirable treatise of 
 Dr. Lionel Beale. 
 
 The operation of Injecting. The various steps in the pro- 
 cess of injecting are very similar, whether the object be 
 treated for the opaque or transparent methods, though in 
 the former instance it must be placed in warm water until 
 the temperature has been sufficiently raised. 
 
 The necessary apparatus will be found as follows : 
 
 A syringe with pipes and stopcocks. 
 
 Conical corks. 
 
 Dissecting knives (Fig. 153). 
 
 Dissecting scissors (Figs. 154-56). 
 
 Forceps (Fig. 158). 
 
 Bull-nose forceps. 
 
 Wash bottle (Fig. 223). 
 
2/0 PRACTICAL MICROSCOPY. 
 
 The first operation is that of finding the vessel we wish 
 to inject, such as the artery of the kidney, or the hepatic 
 vein of the liver. An opening being made, one of the 
 small pipes of the syringe is thrust in and 
 tied round with a piece of waxed silk, so 
 that there may be no danger of withdraw- 
 ing the pipe before the conclusion of the 
 operation. All the vessels communicating 
 with the one in which the pipe is connected 
 must now be tied with silk to prevent the 
 escape of the injecting fluid, and several 
 pairs of bull-nose forceps should be at hand 
 FIG. 223. f r th e purpose of closing any which may 
 
 by accident have been left open. 
 
 Before the pipe is inserted a little of the injecting fluid 
 should be drawn up to fill it. When all is ready, the 
 syringe should be filled and emptied a few times with the 
 fluid in order to get rid of all air, especially below the 
 stopcock, and fitted to the pipe already in the prepara- 
 tion. With a firm pressure the syringe must be about 
 three-fourths emptied, again refilled and injected until the 
 operation is complete. 
 
 When size is employed, after having tied up the vessel 
 where the pipe was inserted, the whole should be left in 
 cold water for five or six hours, in order that the size may 
 thoroughly set, after which sections may be cut as directed 
 in Chap. VIII. 
 
 Injected specimens may be preserved in glycerine or in 
 a mixture of equal parts of alcohol and water, until required 
 for examination ; carbolic acid water is also useful for this 
 purpose. 
 
CHAPTER XIII. 
 THE PREPARATION AND MOUNTING OF OBJECTS. 
 
 WE have now described most of the processes incidental to 
 microscopical research, and which should be applied to 
 specimens in order to gain some insight into their peculi- 
 arities or their structure. No doubt many students will 
 think that we have delayed unnecessarily the preparation 
 of objects for mounting, and the subsequent process whereby 
 they may become permanent objects of interest, and that 
 we have taken pains to describe in detail processes much 
 more difficult than mounting. 
 
 We do not think this. It may be thought an easy opera- 
 tion to place a piece of sea-weed in Canada balsam, and 
 cover it with a circle of thin glass ; or to soak an insect in 
 potash, to squeeze out the internal organs, finally mounting 
 in balsam and benzol ; but this is not the style or class of 
 mounting which we wish to see become general. 
 
 Dr. Pelletan, in a letter to the ' Journal de Micrographie ' 
 (iii., No. 3, p. 139), speaks very strongly of the scientific 
 value of microscopical preparations. In speaking of the 
 method of mounting insects he says : " Others, more in- 
 genious, mount large insects or immense spiders entire after 
 having emptied them of their contents, and these prepara- 
 tions have really a magnificent appearance. But alas ! the 
 integument is all that has been preserved, and the little 
 that remains of the internal organs is represented by a 
 uniform transparent mass, in which the microscopist finds 
 nothing to study." He also adds further on : "I would 
 
PRACTICAL MICROSCOPY. 
 
 not say that all preparations which I call trivial are useless ; 
 most certainly not. If they are not satisfactory to savants 
 they interest amateurs, and they teach many things that 
 otherwise would not have been known. They are also 
 useful in England, where they are sold in large numbers, 
 because among our neighbours the microscope is more used 
 for amusement and as an object of luxury than for working 
 purposes." 
 
 We cannot fully endorse the opinions of Dr. Pelletan, 
 though it would be more satisfactory to find an improve- 
 ment in the general mounting of objects ; and to prepare 
 one or two slides of a subject well would be of far more 
 value than mounting a host of second-rate ones for ex- 
 changes ; and further, we would like to see far more experi- 
 ments upon subjects mounted in different media than exists 
 at present, and what with interchange of opinions upon this 
 subject at our various microscopical society meetings, we 
 could scarcely fail in rendering our cabinets more inter- 
 esting and our preparations more permanent. 
 
 The mounting of objects and their preparation for this 
 purpose is by no means an easy operation, especially if our 
 slides are to be permanent and of scientific interest. The 
 conditions are ever varying, and it requires a good know- 
 ledge of the properties of the various substances generally 
 used in this branch in order to know beforehand what their 
 actions will be on this or that objector portion of it. Even 
 a process which would do well for some particular class of 
 objects is often found to fail with some of them. If, for 
 instance, the marine alga Bangia fusco-purpurea be mounted 
 in balsam and benzol it will represent it in its natural con- 
 dition, while if we try to preserve Dasya coccinea in the 
 same manner we shall fail miserably. In other instances 
 we may find many algae which may be successfully mounted 
 in Deane's medium, while if we try to put up the first- 
 
GENERAL REMARKS. 273 
 
 named algae in it we get nothing but a swollen tube con- 
 taining swollen endochrome. Thus it is that many objects 
 are spoiled by the lack of knowledge of various preparers, 
 and also by the fact that some who should possess this 
 knowledge perform their operations so rapidly that it is 
 impossible they can produce uniform and permanent work. 
 And what do we see when we cast our eyes over the con- 
 tents of various cabinets ? Drawer after drawer is scanned, 
 and if the third of their contents are passable, from a 
 scientific point of mew y the possessor may be congratulated. 
 What can be done to get microscopy out of this groove ? 
 Slower work, more time in preparing, more care, the rejec- 
 tion of all middling or bad slides, the study of the object 
 before proceeding to mount it, mounting but few slides, and 
 last and not least, the careful study of the effects of the 
 various varnishes, cements, and reagents upon each other, 
 and upon the various objects they are intended to preserve. 
 
 For the preparation and preservation of objects for the 
 microscope certain pieces of apparatus are either necessary 
 or useful, and although many makeshifts can be employed, 
 we give illustrations of the various instruments most gene- 
 rally used. 
 
 Objects are generally mounted upon glass slides, or 
 " slips," as they are sometimes called, which measure three 
 inches in length by one in breadth, and of various thick- 
 nesses. They are sold either with rough edges or ground 
 edges as may be required, but there is so little difference in 
 price between the two varieties the latter possessing so 
 many advantages that the student is strongly advised to 
 purchase ground edges only. 
 
 The ordinary flatted crown slips are the cheapest, but 
 should never be used for fine work, those of plate glass 
 being preferable, and even this should be selected if required 
 for mounting objects requiring delicate attention to illumi- 
 
 T 
 
2/4 PRACTICAL MICROSCOPY. 
 
 nation. All kinds are generally fairly clean when received 
 from the dealer, but must, nevertheless, be beautifully 
 polished before any object can be mounted upon them. 
 The thorough cleansing of the glass is an important step, 
 as the slightest film of grease is a preventive of perfect 
 adhesion of any varnish or cement which may be subse- 
 quently used. Ammonia has the power of converting 
 grease into soap, and spirits of wine will dissolve the two, 
 and as some kinds of dirt require friction to remove, the 
 following is perhaps the best formula for a mixture for 
 cleaning slides : 
 
 Liquid ammonia (sp. gr. '880) 10 drops. 
 
 Methylated spirit 2 oz. 
 
 Water oz. 
 
 Rouge, sufficient to make a thin cream. 
 
 Rose-wood slips, also 3 inches long by I broad, are 
 also used for mounting objects, either with sunk cells or 
 with holes bored right through ; but the student will find, 
 perhaps only after a valuable series has been spoiled, that 
 wooden slides possess no advantages over those of glass, 
 and have very many objectionable qualities. 
 
 FIG, 224. 
 
 In mounting objects, a slide-centerer should be employed, 
 in order to make the finish as presentable as possible, as it 
 will generally be found that a slovenly finish means a bad 
 preparation, though this is by no means always the case. 
 The most simple form of centerer is shown in Fig. 224, 
 
SLIDE-CENTERER MEASURING WEDGE. 2?$ 
 
 which is simply a piece of very stiff card, upon which the 
 lines and circles can be drawn. 
 
 Another form of centerer for slides was illustrated in 
 ' Science-Gossip ' for 
 1879, from which the 
 accompanying sketch 
 is taken (Fig. 225) ; 
 the device is so sim- 
 ple that it needs no 
 
 description. 
 
 FIG. 225. 
 
 The object is nearly always covered with thin glass, 
 either squares or circles, and is sold by the ounce in 
 sizes for circles, increasing by eighths of an inch. It is of 
 importance that for high powers used dry the cover-glass 
 should be of uniform and great thinness. When pur- 
 chased they should be selected according to thickness, and 
 each variety used for its special purpose. The thickness 
 may be ascertained in various ways. In one, the cover 
 may be held in the stage forceps edgeways, and measured 
 by observation with the micrometer eye-piece shown at 
 Fig. 202. 
 
 Another method is by the lever of contact as made by 
 Messrs. Ross and Co., or the cover-glass measurer devised 
 by M. Schonemann, called the "measuring wedge," and 
 shown in Figs. 226 and 227. 
 
 FJG. 226. FIG. 227. 
 
 In order to measure the thickness of a cover-glass the 
 instrument should be free from dust, and the wedge drawn 
 back until the cover can be placed between the wedge and 
 
 T 2 
 
276 
 
 PRACTICAL MICROSCOPY. 
 
 the piece d. The wedge is then closed until the motion is 
 stayed by the glass, when the number of the divisions indi- 
 cating the thickness can be read off. 
 
 None but the very thinnest glass can be used with the 
 dry A- and -^ objectives ; it is much more expensive and 
 difficult to cut than ordinary cover-glass. 
 
 Cells and Cell-making. Many objects requiring to be 
 permanently mounted are of such a thickness that the thin 
 cover needs some support at its edges, or again others are 
 better preserved when mounted in fluids, and for these pur- 
 
 FIG. 228. 
 
 poses cells are employed. These are of several kinds, but 
 may be conveniently divided into three classes, varnish 
 cells, solid, and built-up cells. 
 
 The cell-making machine was originally devised by Mr. 
 Shadbolt, as a simple brass circular plate about three inches 
 in diameter, upon the surface of which was placed a pair of 
 
TURNTABLES. 
 
 277 
 
 springs for the purpose of holding down the glass slip ; it has 
 been the parent of several forms supposed to be of great 
 benefit to the microscopist. In order that the slides may 
 be easily centered, the table is usually engraved with a 
 series of circles ; but it is readily seen that such centering 
 can only be approximate. 
 
 In order to centre the slides accurately in one direction, 
 that of width, Zentmayer introduced the simple device of 
 fixing a couple of pins equidistant from the centre and at 
 opposite sides of the table, the slide being so arranged that 
 it touched both of these pins. This centres for the width, 
 and in length this is accomplished by a series of circles near 
 the edge of the table, the operator making the adjustment 
 from inspection of these. 
 
 In 1870 Dr. Matthews devised a turntable (Fig. 228) to 
 accurately centre slides in the direction of their width, and 
 this possessed the further advantage that no springs or 
 other portions of the table rose above the slide, to catch 
 the fingers or brush, during its revolutions ; and in the next 
 year Mr. J. B. Spencer, in a 
 communication to 'Science- 
 Gossip,' showed how this 
 might be made in hard wood 
 by the microscopist himself. 
 
 In ' Science - Gossip ' for 
 1874 Mr. Bridgman described 
 and illustrated a form of turn- 
 table (Fig. 229) which, though 
 not self-centering, enabled a 
 slide to be always placed in 
 the same position upon it, so 
 far as the centre of rotation went. In 1875 Mr. C. F. Cox, 
 of New York, devised a self-centering turntable, con- 
 sisting of the circular revolving plate, in which was cut a 
 slot in the direction of its diameter, and in this were 
 
 FIG. 229. 
 
2?8 PRACTICAL MICROSCOPY. 
 
 moved, by means of a right-handed and left-handed screw, 
 a pair of clips which gripped the opposite and extreme 
 corners of the slip, as shown in Fig. 230. 
 
 It will thus be seen that so long as the edges of the slip 
 are at right angles to each other the centering must be 
 absolutely accurate, but not otherwise. 
 
 FIG. 230. 
 
 On the introduction of this machine several operators 
 objected to the method of holding the slip, and Kinne soon 
 afterwards introduced his modification (Fig. 231), in which 
 the two corner clips were drawn together and made to grip 
 the glass slip by means of an indiarubber band or spiral 
 spring. 
 
 In 1876 a notice appeared that Mr. Charles Butterworth, 
 of Shaw, near Oldham, exhibited at the annual soiree of 
 the Oldham Microscopical Society a turntable capable of 
 making cells of either circular or elliptical form ; and also 
 by its aid a thin cover-glass could be held in position on a 
 cell, whilst the various rings of cement or varnish could be 
 put on. It is constructed upon the principle of the " oval 
 chuck," and so enables either circles or ovals to be traced 
 with ease moreover, it may also be used for cutting thin 
 glass covers, either oval or circular, as well as for general 
 mounting purposes. 
 
TURNTABLES. 
 
 279 
 
 A turntable of exactly similar make is now sold by 
 Messrs. Armstrong, of Manchester ; it is shown in Fig. 232. 
 
 FIG. 231. 
 
 Mr. Sidle exhibited, in 1878, at the Microscopical Con- 
 gress at Indianapolis, a turntable, which has since gone by 
 
 FIG. 232. 
 
 the name of the " Congress " turntable. It may be seen in 
 Fig. 233. 
 
 Into the upper surface of the rotating plate, diametrically 
 
280 PRACTICAL MICROSCOPY. 
 
 opposite and equidistant from the centre, two circular 
 plates or discs, one inch in diameter, are set, their surfaces 
 flush with that of the large plate. Pivots from the two 
 discs project through the plate, and each carries upon the 
 
 FIG. 233. 
 
 lower side of the plate a toothed wheel. A hollow sleeve, 
 rotating free upon the stem of the table, carries a third 
 and larger wheel, which gears into the two others, and 
 thereby gives rotation to the discs in the top of the plate. 
 
 Near the opposite edges of the two discs, the angular 
 jaws which hold opposite corners of the slide are pivoted 
 (as in Cox's and other forms of tables), and it will be seen 
 that by giving rotation to the central wheel, under the 
 plate, the jaws may be made to approach or recede at 
 pleasure. 
 
 A coiled steel spring, concealed within the hollow 
 sleeve, serves to close the jaws, while the single motion 
 of a milled head upon the sleeve opens them to their full 
 extent. 
 
 It may be also seen that although the jaws do not 
 approach in a straight line, yet, when properly adjusted, a 
 line joining the pivots of the jaws will cut the centre of 
 the plate, whatever the position of the jaws ; and they 
 being always equidistant from the centre, it follows that 
 
TURNTABLES. 281 
 
 the slide, when clasped between them, must be perfectly 
 centered. 
 
 In 1879, Mr. Rolfe re-invented Kinne's turntable, and 
 described the same before the members of the Quekett 
 Club, adding at the same time an idea of his own, which 
 was quite novel, and is illustrated in Fig. 234. 
 
 FIG. 234. 
 
 The year 1880 saw the introduction of two turntables, 
 the first by Mr. Dunning (Fig. 235), which has since 
 been made by Mr. Swift, and the second introduced by 
 Dr. Matthews. Mr. Dunning's turntable will take any 
 slides up to two inches in width, and also serves for 
 retouching slides, the circles upon which are not truly 
 central. Dr. Matthews' last production is to be found 
 fully described in the ' Journal of the Royal Microscopical 
 Society,' and as it only consists of a method of driving 
 the table, it will be of but little use mentioning it here in 
 detail. 
 
 Another good form of self-centering turntable has lately 
 
282 PRACTICAL MICROSCOPY. 
 
 been introduced by Mr. H. P. Aylward, of Manchester, 
 and may be said the simplest, least expensive, and best 
 self-centering turntable extant. 
 
 FIG. 235. 
 
 The author, from actual experience, can recommend it 
 as being the turntable for all the wants of the microscopist. 
 Mr. Aylward calls it the " Concentric." It essentially 
 consists of two plates, the inner revolving on a pivot, 
 whilst the outer revolves concentrically on the inner, .a few 
 small pins being so arranged that by a single turn of the 
 outer ring they firmly grasp the glass slide, and cause its 
 centre to exactly coincide with the centre of the turntable, 
 whilst a simple reverse movement instantly liberates it. 
 This turntable answers for slides of various widths, from 
 I inch to 2j inches, it is strongly made, and well finished, 
 besides which loose springs are supplied, fitting into corre- 
 sponding holes in the turntable, convenient for making 
 rings in any other position than that of the true centre of 
 the slide. 
 
 This instrument is shown in Fig. 236, the letters being 
 explained as follows : 
 
 A, ordinary wood block with steel pivot, on which the 
 brass table revolves. B, two brass springs which fit into 
 holes in the table, and may be used when the slide is 
 required to be out of centre ; when not in use they fit 
 into holes in the wood, as shown above. D, revolving 
 
CELL-MAKING. 283 
 
 table, with milled wheel below for rotation. H, brass 
 annulus or ring revolving concentrically on the table D ; 
 on the ring H are screwed two conically headed pins, J J, 
 3A of an inch apart exact, to allow the 3 x i slip to be 
 placed diagonally between them. F F, two similar pins in 
 
 FIG. 236. 
 
 plate D, so placed, that upon revolving the ring H they, in 
 conjunction with the pins J J, firmly grasp the opposite 
 corners of the glass slip, and cause the centre to coincide 
 with the centre of the table D. I, brass pin for more 
 easily revolving the ring H, for securing and liberating the 
 glass slip, which is done by moving the ring H in the 
 opposite direction. 
 
 Let us now turn our attention to the practical operation 
 of cell-making. To commence with varnish cells place 
 the slide upon which the cell is to be made between the 
 pins upon Aylward's turntable, and make three rings 
 thereon (of the diameter the cell is to be when finished) 
 with a writing diamond : this operation is to roughen the 
 slip, and cause more perfect adhesion of the varnish. Now 
 take up a good brushful of varnish, and spinning the table 
 round, deliver it where the rings have been cut, in such a 
 manner that it stands up like a wall, and does not spread 
 itself more than is necessary over the slide. So soon as 
 this layer is dry and perfectly hard, another layer -may be 
 put on, and the process repeated until the cell has acquired 
 sufficient depth. The cell now requires drying or baking 
 
284 PRACTICAL MICROSCOPY. 
 
 at a gentle heat over a long period, and this can be 
 
 easily accomplished in the hot-air chamber shown in 
 
 Fig. 237. 
 This piece of apparatus is not absolutely necessary, 
 
 though it is of much assistance. By means of a spirit- 
 lamp or gas-burner almost any 
 temperature can be maintained 
 for lengthened periods, a thermo- 
 meter inserted into the air space 
 serving to measure the degree 
 of heat ; it serves many useful 
 purposes, and is certainly better 
 and more uniform than the " cool 
 
 oven " so often recommended. 
 FIG. 237. 
 
 The varnish of which a cell is 
 
 constructed must vary according to the nature of the 
 medium it is to hold; for objects mounted dry and not 
 very thick, a brown varnish cell is all that is required (see 
 receipt, Chapter XIV.), or it may be made of asphaltum, 
 marine glue, or gold-size, at the fancy of the operator. 
 
 The gold-size cell requires no baking, the hardening is 
 due to an oxidation process, and wherever used it forms a 
 most reliable cell. Varnish cells should be made some 
 time before they are required, in order that no change 
 takes place after the cover-glass has been put on. 
 
 Deeper cells are constructed of glass, ebonite, tin, 
 ivory, brass, and several other substances; the glass slip 
 forming the base of the cell should be roughened as 
 before mentioned, the cell-ring roughened on each side, 
 and then cemented to a glass slip with gold-size or brown 
 varnish. 
 
 The 'student is advised to eschew all paper, cardboard, 
 and wax-cells : varnish is the safest to use for thin cells, 
 and glass, pure tin, or ebonite for the deeper ones, and if 
 
MOUNTING OBJECTS DRY. 285 
 
 care be taken to roughen the surfaces of contact, the 
 tendency to leak when filled with fluid will be much 
 reduced. A considerable number of cells of various 
 diameters and depths should be made at one sitting, and a 
 stock of old cells always kept on hand. If new ones are 
 used they often turn out unsatisfactorily. 
 
 Large cells may be made of four separate walls of glass 
 all ground together to one level, cemented by their corners 
 to the glass slide with marine glue. In using marine glue 
 the surfaces to be united should be heated very hot, the 
 marine glue applied to the edges, and kept firmly pressed 
 together until set. They may then be further heated in 
 the bath, Fig. 237, for twelve hours. 
 
 In passing now to the mounting of objects, the reader 
 will see the impossibility of describing how any particular 
 object or class of objects may be successfully mounted ; 
 which is the best of the several methods can only be 
 discovered in actual practice, and if the salient points in 
 each method of mounting be described, the student will 
 no doubt learn much that will help him with other 
 subjects. 
 
 For this reason the mounting of objects has been divided 
 into three sections 
 
 1. Mounting dry. 
 
 2. Mounting in gum resins. 
 
 3. Mounting in aqueous media. 
 
 DRY MOUNTING. In treating of dry mounting we may 
 so subdivide the work as to show the isolated operations 
 upon which success depends, and in doing so, the student 
 will see the importance of thoroughly understanding the 
 why and the wherefore of each operation. These may be 
 described as follows : 
 
 Cleaning the Specimens. This is a section upon which a 
 
286 PRACTICAL MICROSCOPY. 
 
 moderate-sized volume may be written, as it applies to all 
 objects whether mounted dry, in gum resins, or in aqueous 
 media, and may be simply described as an operation for 
 eliminating matter in the wrong place dirt. Foreign 
 matters should be eliminated as much as possible, and 
 really when set about in the right way it is not very difficult. 
 When we come to compare the slides of diatoms put up by 
 Cole, Redfern, or Redmayne with many home-mounted 
 slides it may be readily seen what is the effect of a little 
 care on the part of the preparer. Cole's exceedingly clean 
 gatherings, his hand-picked slides, Redfern's single diatom, 
 mounted on a J-inch cover in the centre of a red circle -^ of 
 an inch in diameter, and Redmayne's diatom slides all 
 deserve imitation. 
 
 Let us turn again to the mounting of mosses : how many 
 of the ol TroXXot are content with placing the specimen in 
 glycerine jelly, dirty as when collected, making no effort 
 at all to divest it of its useless and degrading accompani- 
 ment ! 
 
 It is to be hoped that these few words will act as an 
 incentive to cleanly working ; all the requisites are several 
 camel's-hair or sable pencils, one of which should be cut 
 short so that the hair projects but a quarter of an inch 
 beyond the quill-holder. The knives, scissors, forceps, 
 needles and other articles have been already described in 
 the chapter on dissections ; it may, however, be necessary to 
 state that each article should be kept for its specific uses, as 
 if knives, scissors, and needles be used for mounting pur- 
 poses they will soon be out of order for dissections. 
 
 Most objects can be cleansed under water with the 
 brushes and needles in the small dissecting troughs shown 
 in Fig. 152; these can be used under a watchmaker's eye- 
 glass or on the stage of the microscope under a half-inch, 
 with erector such as has been already described. 
 
DRYING THE PREPARATIONS. 287 
 
 Before being finally finished, every slide should be examined 
 under that power most suited to show its characteristics, and 
 if it is defective in any way it should be discarded and washed 
 off the slip. 
 
 The final washing of an object treated with water or 
 any aqueous fluid should be made with distilled water 
 ordinary water leaves more or less residue, which interferes 
 with the brilliancy of the preparation. 
 
 Drying the Specimens. The moisture can be abstracted 
 from many substances by contact with a fluid such as 
 alcohol in a small corked tube, but in many instances this 
 is not admissible, so that a desiccator becomes necessary. 
 The form used by the author is shown at Fig. 238. It 
 consists of a mahogany base- 
 board, in which a circular groove 
 is turned to admit the bell-jar 
 standing over it. This groove 
 is filled with mercury, which 
 acts as a lute and cuts off all 
 connection with the outer air. 
 
 Under the bell-jar, and standing FlG 23 & 
 
 upon the base-board, is a vessel 
 
 containing concentrated sulphuric acid, one of the most 
 
 powerful absorbers of water we have. A shelf is fixed 
 
 over the acid, upon which are laid the slides requiring 
 
 desiccation. 
 
 Unless the operator is careful and has a safe place to 
 keep the desiccator, he had better choose another pattern, 
 as concentrated sulphuric acid is a fluid not to be 
 spilled with impunity, and quicksilver is an extremely 
 awkward metal to pick up from the floor upon which it may 
 have been dropped accidentally. The sulphuric acid may 
 be replaced by fused chloride of calcium, carbonate of 
 potash, or even by quicklime broken in pieces the size of 
 
288 PRACTICAL MICROSCOPY. 
 
 hazel nuts ; but the apparatus is not then quite so effective 
 or rapid. 
 
 The mercury may indeed be dispensed with altogether 
 by the use of a plate of ground-glass in lieu of the grooved 
 base-board, but in this case the bell-jar must have a strong 
 and well-ground welt round its open mouth, perfect adhesion 
 between the two being secured by means of a coating of 
 grease. 
 
 There is a very good form of desiccator which may be 
 obtained from almost every dealer in chemical apparatus. 
 The lower portion contains the desiccating material, over 
 which is placed a sheet of perforated zinc, while the cover 
 is ground truly, and fits as a cap or lid upon the lower half. 
 Perhaps this form would suit the majority of our readers, 
 more especially if combined with the use of chloride of 
 calcium as the desiccating agent. 
 
 The preparation to be dried is placed upon the shelf 
 (Fig. 238) above the desiccating material, covered with the 
 bell-jar, and left to itself for twelve or twenty-four hours. 
 
 In dry-mounting it is absolutely necessary to eliminate 
 all the moisture, for many objects mounted in a damp state 
 often become covered in a few months with a dense growth 
 of fungi, or the cover-glass becomes obscured to such an 
 extent that the object is seen as through a fog. This often 
 happens also when a cardboard cell or wooden slide is 
 used. 
 
 Let us now proceed to illustrate the foregoing by the 
 process for mounting diatoms given in the 'American 
 Journal of Microscopy,' April 1880. 
 
 The process of cleaning diatoms requires time, skill, 
 patience, and personal experience, in addition to what may 
 be learned from others. After trying for a long time to 
 dispose of sand and mud the novice will be more careful in 
 collecting. After an explosion or two, involving the loss of 
 
CLEANING DIATOMS. 289 
 
 valuable material, and possibly the destruction of clothing, 
 he will learn that strong acids and other chemicals are not 
 to be handled like water. Experience makes the process 
 safe and comparatively easy, requiring but a few minutes' 
 attention at a time. No one method will apply in all cases, 
 for some gatherings are imbedded in stone, some cemented 
 with lime, which require special attention, while many 
 gatherings require nothing more than a strong heat to 
 destroy the organic matter and leave them ready for 
 mounting. 
 
 In recent gatherings, when the diatoms are clean, put 
 them into a bottle containing equal parts of alcohol and 
 water, where they may be kept as long as desired. When 
 ready to transfer them to slides, all that is required with 
 most varieties is to dip a few from the bottle with a pipette, 
 to put them on the thin cover-glass, and after placing the 
 glass on a strip of mica or of tintype, keep the whole at a 
 red heat until the organic matter is destroyed and only the 
 shells remain in white powder. 
 
 Another method is to boil for thirty to sixty minutes in 
 strong soapsuds, afterwards washing thoroughly in soft 
 water to get rid of foreign material, such as sand, flocculent 
 matter, &c. On examination of the material, if organic 
 matter be still present, put the mass into a test-tube or 
 other suitable vessel, and, after settling, completely turn 
 off all supernatant water, adding four or five times its bulk 
 of nitric acid, and while boiling throw in small fragments 
 of bichromate of potash to bleach. Some prefer chlorate, 
 but the bichromate is sufficient, and danger of explosion is 
 avoided. When the organic matter has been destroyed, a 
 higher temperature will be required to boil the acid, indi- 
 cating that no more is needed. Probably five or ten 
 minutes will be sufficient. Wash in rain-water, or that from 
 melted ice, until a drop evaporated on a slide shows no 
 
 U 
 
290 PRACTICAL MICROSCOPY. 
 
 residue around the edge, leaving a clean slide of diatoms. 
 Never use hard water, for the lime in it will cause all 
 flocculent matter to cohere in masses. 
 
 The methods given are all that is required for a large 
 proportion of diatomaceous material so far as disposing of 
 organic matter is concerned. The sand and other inde- 
 structible matter must be eliminated by gravity. 
 
 Guano, Monterey stone, material containing lime, &c., 
 require harsher treatment and much more time. 
 
 Guano should be boiled at least two hours in soft water, 
 or as long as any colouring matter can be turned off; then 
 proceed as in fossil earths. 
 
 Stonelike masses must be broken down by boiling in a 
 strong solution of soda crystals. After disintegration wash 
 and boil for twenty to thirty minutes in strong nitric acid* 
 and while yet boiling add about an equal quantity of 
 muriatic acid, continuing the boiling for from twenty to 
 thirty minutes longer. After washing out the acids boil in 
 pure sulphuric acid until the mass becomes inky black, then 
 throw in fragments of bichromate of potash, and continue 
 the boiling until it becomes clean. If, on examination with 
 the microscope, it is found there is much flocculent matter 
 besides the diatoms and sand, it can be removed by boiling 
 for a few seconds in caustic potash, and then turning almost 
 instantly into plenty of soft water to destroy the action of the 
 potash. The diatoms are now chemically free from all organic 
 matter, and they may be dried and kept in small phials in 
 powder, or be put into equal parts of alcohol and water, 
 and kept for future separation from sand and other inorganic 
 matter, or we can proceed at once to isolate the diatoms, 
 also to separate into sizes. To do this, put the cleaned 
 diatoms into a small bottle, fill with soft water, filtered, and 
 after shaking thoroughly turn off all that floats after five 
 seconds into a larger bottle. Repeat the process, and after 
 
CLEANING AND MOUNTING DIATOMS. 291 
 
 some five or six repetitions we shall find very little but 
 sand in the first bottle ; this we will throw away unless 
 some very large diatoms remain, which can be removed by 
 drying on a slide and picking with a mechanical finger. As 
 soon as the material in the large bottle has settled, turn off 
 the water and return the material to the small bottle and 
 repeat the process, allowing longer time to settle. This 
 process may be repeated five or six times, or as many times 
 as necessary to make the separation satisfactory, allowing 
 more time on each repetition to settle. Another excellent 
 method is used by Christian Febiger, of Wilmington, Del., 
 whose arranged slides have attracted much attention. 
 Strain through No. 18 bolting cloth to obtain large diatoms. 
 The remaining small diatoms and sand must be placed with 
 water in a clock crystal and rotated. The sand will go to 
 the bottom, and the diatoms can be poured off repeatedly 
 until as clean as desired. 
 
 It will be impossible to save all the diatoms in the 
 repeated washings. So long as 100 slides can be mounted 
 from a mass not so large as a small pea, be content to save 
 time and patience by losing a tithe of the harvest. Do not 
 be disappointed when you find hardly enough diatoms 
 remaining to make a fair thickness of carpet in your phial, 
 for if clean you will have sufficient for yourself and for 
 several of your friends, even then. 
 
 For mounting, always place with a pipette a drop of 
 the fluid containing them upon the cover-glass, and never 
 on the slide. Professor Hamilton L. Smith is the author 
 of the following excellent method. Cut a piece of 
 photographer's tintype into strips about I inch wide 
 and 3 inches long, then cut away all except enough for a 
 handle, leaving I inch square on one end ; bend the end of 
 this handle, and fasten into a cork in a bottle, which will 
 serve for a holder. Upon this plate place the clean cover, 
 
 u 2 
 
PRACTICAL MICROSCOPY. 
 
 and by means of a pipette drop a little of the dilute alcohol 
 and diatoms upon it, applying a gentle heat with a spirit- 
 lamp. The alcohol takes fire and burns off. The remaining 
 alcohol causes the diatoms to become evenly distributed. 
 If inclined to mat, touch with a hot pin or needle. Now 
 bring the whole to a red heat for plenty of time to make 
 the diatoms appear white and perfectly clean. 
 
 Now take a thin glass slip upon which a very thin cell of 
 brown varnish has been made and well aged as previously 
 described, take up the thin cover with diatoms attached and 
 place it upon the slightly gummed end of a cedar-wood 
 pencil, the diatomed side being uppermost. Now with a 
 fine sable pencil coat the edge of the thin cover with a 
 layer of thick brown varnish, wait until it has nearly set, and 
 invert it carefully and firmly upon the cell-walls of the slip. 
 A slight pressure with the pencil will cause the cover to 
 adhere all round, when the slide may be set aside for about 
 half an hour ; it must then be placed on the turntable and a 
 slight coat of brown varnish applied to the edge of the circle. 
 
 The slide should now be put away for a week or more, 
 after which time it should be examined with the power 
 suitable to it and if not satisfactory, discarded. If, on the 
 other hand, it is a good preparation, the student may pro- 
 ceed to finish it by placing it on the turntable and describing 
 a ring of white zinc varnish so as to cover the edges of the 
 circle, making it completely air-tight. When this is dry, 
 various coloured rings may be turned upon the white sub- 
 stratum, giving the whole a very pleasing appearance. 
 
 Some writers have deprecated this ornamentation of 
 slides, but the author's opinion is that the time is well spent 
 over a good slide, while a bad one, or even one of medium 
 quality, should be washed off as soon as examined for the 
 first time. The composition of the coloured varnishes may 
 be found in the list of recipes at the end of this chapter. 
 
ZENTMA YERS MECHANICAL FINGER. 293 
 
 The process of arranging diatoms is a simple one, easily 
 done by means of a small camel's-hair pencil, with the aid 
 of the erector and a half-inch objective. The brush should 
 be drawn through the lips, and when using the microscope- 
 stand shown in Fig. 24, sitting well over it, the side of the 
 hand only resting on a support, it is quite easy after a little 
 practice to remove any diatom from the field of view. 
 For this purpose many workers use what is called a 
 mechanical finger as a substitute for the fingers of the 
 human hand. Zentmayer's form has been described in the 
 ' Monthly Microscopical Journal/ and is here reproduced as 
 Fig. 239. 
 
 FIG. 239. 
 
 Rezner's form of this instrument (Fig. 240) is much more 
 simple than the above, and may be adapted to any micro- 
 scope. It consists, as may be seen in the engraving, of a 
 sleeve, which is passed up over the objective just far enough 
 to possess a firm bearing, and so that the point of the 
 bristle is in focus when depressed to nearly its full extent. 
 In order to use this finger, the point of the bristle should 
 be brought into the centre of the field, touching the object 
 slide, and then withdrawn, still in the axis of the micro- 
 scope, until it has become invisible. The desired object is 
 
294 PRACTICAL MICROSCOPY. 
 
 then sought for, such as diatoms, foraminifera, or other 
 minute specimens, and brought into the centre of the field; 
 the point of the bristle is then lowered by the screw until 
 it touches the desired object, which usually adheres to it at 
 once. 
 
 FIG. 240. 
 
 Some operators recommend a cat's whisker for the pur- 
 pose of using with the mechanical finger, and no doubt it is 
 as good as anything. Still the worker with this piece of 
 apparatus will find that often, especially when working 
 with ordinary bristles, it is almost impossible to deposit the 
 object exactly where it is required, so pertinaciously does it 
 adhere to the bristle. Prof. H. L. Smith has advised the 
 use of a slender thread of glass for this purpose, but taking 
 all things into consideration the cat's whisker seems to be 
 the best. 
 
 The diatoms are picked one by one and placed where 
 desired. To prepare the slide, put it on a turntable, and 
 with a pen make a small circle in the centre to guide in 
 placing. On the reverse of the slide put a tiny drop of 
 pure distilled water, with a small fragment of gelatine in 
 it ; so that when the diatoms are arranged, breathing on 
 them will bind them into the size. Foraminifera, Poly- 
 cistina, and other similar objects may be arranged in the 
 same manner. 
 
 As another instance of dry preparation may be given a 
 method for mounting starch granules. The starch, say 
 
DRY MOUNTING. 
 
 295 
 
 from the potato, should be well washed from all foreign 
 substances, and mixed with cold distilled water, so as to 
 form a slightly opalescent liquid A thin glass cover 
 having been cleaned is breathed upon, laid level upon the 
 table of the desiccator (Fig. 238), and a drop of the 
 starch solution deposited upon it. When perfectly dry 
 it may be coated at the edges with brown varnish, and 
 inverted upon a shallow varnish cell, as has already been 
 described for diatoms, and finished in the same manner. 
 
 Such specimens as micro-fungi, Penicillium glaucum (/), 
 P. roseum (n], Ascophora mucedo (/), P. chartarum (/), 
 Aspergillus glaucus (m), Fig. 241, can only be successfully 
 
 FIG. 241. 
 
 mounted by the dry method, as when mounted in fluid the 
 spores become detached, and the chief characteristics are 
 lost. 
 
 The best way to mount such specimens would be to 
 choose a cell deep enough to hold them comfortably, and 
 
296 PRACTICAL MICROSCOPY. 
 
 place a small drop of Farrant's medium in the centre, to 
 which is attached a portion of the substratum bearing the 
 fungus upon it. The slide must now be placed under the 
 desiccator until perfectly dry, when the thin covering glass 
 should be placed on in the manner already described, and 
 finished in the usual way. 
 
 There is another style of mounting it may be useful to 
 describe, i. e. in such a manner that the Lieberkuhn may be 
 used with the slide, to produce illumination on a dark 
 ground, so that such objects as Foraminifera or the pollen 
 of the mallow may be viewed with this appliance, as an 
 opaque object 
 
 Take a very shallow varnish cell slip, but deep enough 
 of course to contain the object, and turn upon the centre of 
 it a disc of Bate's dead-black varnish, allow this to dry and 
 become well aged. When proceeding to mount, say the 
 pollen of Althea roses (Fig. 97), dust it over this blackened 
 disc, place in the desiccator until dry, and then put on the 
 cover in the usual manner. If the pollen be dusted over 
 the whole of the circle, the observer will be able to use 
 the slide both as a transparent and opaque object. Many 
 preparations, such as the disc of deal, do not require fixing 
 either to the cell or its cover, and this class of objects 
 requires no special directions for successful mounting. 
 
 MOUNTING IN GUM RESINS. Objects required for 
 mounting in gum resins need of course quite as much 
 preparation as when put up by the dry method ; but that 
 we are about to describe is perhaps the best suited for 
 beginners, as the gum resins are good preservatives, and 
 the preparations are likely to be permanent with the 
 minimum amount of care. 
 
 Canada-balsam has been used for a long period for this 
 style of mounting, either by itself or when diluted with 
 chloroform or benzol. 
 
MOUNTING IN BALSAM. 297 
 
 We will here go through the operation of mounting a 
 rock section in undiluted balsam, just to illustrate the only 
 case in which the author advises the use of papers to cover 
 up the whole of the slide. 
 
 A hot-water plate is used by a great many mounters. 
 It may be a tin box 9 inches square by 2 inches in depth, 
 supported on a stand or upon four legs. In one corner is a 
 funnel-shaped neck for the introduction of water and the 
 escape of steam when in use, the chest being heated by 
 means of a gas-burner or spirit-lamp. 
 
 Bell-jars are sure to be required for many purposes, but 
 principally for keeping the dust from objects which are 
 undergoing preparation. They neeo? not be large, and 
 broken wine glasses may be well utilised for this purpose 
 if the stem only is broken. 
 
 When speaking of the hot- water box, perhaps we should 
 have mentioned the hot plate, which is still a favourite 
 with many mounters, who still cling to undiluted balsam. 
 This is a brass plate, standing upon four legs, and is 
 usually heated by means of a spirit-lamp, though there is 
 no reason why it should not be heated by gas. 
 
 The reader will remember that when treating of section- 
 cutting, the surface of the slice first polished was to be 
 cemented firmly to a glass slip, the final grinding being 
 performed upon it. When grinding a section to extreme 
 thinness, the slip is often badly scratched, and thus dis- 
 figured ; some operators advise the section to be taken off 
 this slip, and put upon another for permanent mounting, 
 but in many cases this is not admissible, and the following 
 method should be adopted. Take the glass slip with the 
 section upon it and clean the surface with water, and 
 after with methylated spirit ; place a tiny drop of balsam 
 (rendered fluid by heat) upon the centre of the section, 
 carefully put on the cover and place the whole on the 
 
2Q8 
 
 PRACTICAL MICROSCOPY. 
 
 MOUNTED BY 
 
 GEORGE E, DAVIS 
 
 Boiler 
 
 Incrustation. 
 (Section.") 
 
 hot plate, gently press down the cover, keep on the 
 
 hot plate for a short time and take away to a cool 
 
 place to set. 
 
 No more balsam should be used than sufficient to reach 
 to the edges of the glass cover, and if this 
 point be carefully attended to, the slip will 
 require no cleaning preparatory to covering 
 with paper. 
 
 The covers used and recommended by 
 the author may be seen as annexed. 
 
 These covers should be cut about ^ of 
 an inch less than the slide they are intended 
 to cover, leaving the edges of the glass ex- 
 posed; there is no use in binding up the 
 glass in paper, it only helps to absorb 
 moisture, and in the case of many objects 
 mounted dry, serves to encourage the 
 growth of mildew. 
 
 When mounting in pure balsam, espe- 
 cially if old, the slide gets very hot, so 
 
 that the American clip shown in Fig. 242 is a convenient 
 
 article. 
 
 Catalogue No. 611. 
 Date 10/3/80. 
 
 Medium 
 Balsam. 
 
 Cell 
 
 FIG. 242. 
 
 It has already been shown under the head of dry 
 mounting how diatoms are distributed over the surface 
 of a thin cover. They may also be mounted in balsam. 
 
 On the centre of the glass slip place a tiny drop of old 
 balsam, and with a pair of tweezers place the cover-glass 
 
MOUNTING IN BALSAM AND BENZOL. 299 
 
 over it and hold the whole over the spirit-lamp until a sea 
 of the bubbles is seen underneath. Remove, and with a 
 gentle pressure press down the cover. The bubbles will 
 all disappear and the balsam become hard. To secure the 
 diatoms all in the same plane, turn the cover-side down- 
 wards, and leave in a warm place. This is best effected 
 in the whalebone clip shown by Fig. 243, but care should 
 be taken that the balsam does not project beyond the 
 
 FIG. 243. 
 
 cover, or it will stick to the whalebone, and cause consi- 
 derable annoyance. 
 
 The old plan of mounting objects in pure Canada 
 balsam has been almost abandoned ; it is now usual to 
 put up objects in balsam and benzol whenever balsam- 
 mounted objects are required. 
 
 To illustrate how this should be done, let us proceed to 
 mount one of the forelegs of the great water-beetle (Dytiscus 
 marginalis) shown in Fig. 244. 
 
 After detaching the leg of the insect, the first operation 
 is to soak it in potash solution for a day or two, then take 
 it out and wash it in water, allow it to soak in dilute spirit 
 (i of spirit to 3 of water) for 24 hours, and then transfer 
 it to methylated spirit. After remaining here until all the 
 moisture has been extracted by the spirit it must be taken 
 out, drained on blotting paper, and placed in oil of tur- 
 pentine. Here it must remain until the colour of the 
 chitinous skeleton has become sufficiently reduced, when it 
 
300 
 
 PRACTICAL MICROSCOPY. 
 
 may be soaked for a few hours in benzol to remove the 
 excess of turpentine. It is now ready for mounting- 
 Place a very small drop of balsam and benzol upon the 
 
 centre of a glass slip, take 
 up the leg by means of a 
 pair of forceps, and place 
 it upon the drop of balsam ; 
 now put another small 
 drop of the medium upon 
 the object, and taking up 
 the well-cleaned covering 
 glass with the forceps drop 
 it carefully upon the object 
 in a perfectly horizontal 
 manner. Now gently press 
 down the cover with a 
 camel's-hair pencil in such 
 a manner that the object 
 is not disturbed, and put 
 on the spring mounting 
 clip, as shown in Fig. 245. 
 The slide should now be heated over a spirit-lamp until 
 the benzol just commences to boil, when it must be re- 
 moved to a cool spot to 
 thoroughly set. 
 
 The author's practice is, 
 
 FlG 2 - now, to set the slide on one 
 
 side for a few weeks, then to 
 
 clean off the excess of balsam with a scalpel, finally 
 cleansing by slight friction with a piece of cotton wool 
 or sponge moistened with methylated spirit. After another 
 repose for a few days, the slide is placed on the turn- 
 table, and a coating of brown varnish applied, so that the 
 circle embraces the edge of the cover and the slide also, 
 
 FIG. 244. 
 
MOUNTING IN DAMMAR AND BENZOL. S^ 1 
 
 when it may be finished with the white zinc varnish and 
 coloured rings as already described. 
 
 Balsam and benzol may be used cold, but as the operation 
 is exactly similar to that of mounting in dammar and 
 benzol it will not be further described. 
 
 The operation of mounting wheat-starch in dammar and 
 benzol will sufficiently explain the cold process of mounting 
 objects in gum resins. Make a mixture of wheat-starch and 
 distilled water, as before advised for potato-starch ; place a 
 drop of this upon the centre of a glass slip, and put in the 
 desiccator (Fig. 238) to thoroughly dry. Now take a drop 
 of benzol and place upon the starch, and before it has time 
 to thoroughly evaporate drop on a little dammar and 
 benzol, put on the glass cover, place the spring clip upon it 
 and set aside for several weeks, when the excess of dammar 
 may be removed and the slide finished as already described. 
 Where many objects are required to be mounted at once, 
 spring clip boards may be used. Many forms have been 
 devised, but that figured in ' Science-Gossip ' for October 
 
 FIG. 246. 
 
 1 88 1 is one to be preferred. It is shown in Fig. 246: A 
 being a base-board of mahogany, C pieces of clock-spring 
 bent at each extremity and fitted into corks at D. At E 
 are four screws which admit of several of these boards being 
 
302 
 
 PRACTICAL MICROSCOPY. 
 
 placed above each other without coming in contact with 
 the springs. 
 
 This board may be found of much use, but it is certainly 
 better in many instances to have small independent clips 
 capable of being placed in the hot chamber, air-pump, and 
 similar situations with the slide itself. Many objects may 
 be mounted in gum resins, and the dammar and benzol will 
 perhaps be the best substance generally for objects requiring 
 to be shown with the aid of the polariscope. 
 
 Sometimes with gum resins a source of annoyance is the 
 appearance after a time of a white cloudiness, completely 
 ruining many otherwise carefully mounted specimens. 
 This is caused by dampness, or the presence of fatty 
 matters not carefully removed before applying the balsam. 
 If the foregoing instructions be carefully followed this 
 mishap can scarcely happen. 
 
 FIG. 247. 
 
 Cotton fibres and sections of the same, shown in Figs. 247 
 and 248, make good polariscope objects when mounted in 
 
 FIG. 248. 
 
 dammar and benzol ; they should be soaked in spirit to 
 remove water, transferred to benzol and mounted direct 
 from that fluid. 
 
 Dust and dirt are the greatest enemies of the micro- 
 scopist, and every operation which can be done under cover 
 
MOUNTING WITHOUT PRESSURE. 3O3 
 
 should be so arranged. In these cases very small but wide- 
 mouthed bottles are conveniences, watch-glasses, small 
 beakers, and stemless or footless wine-glasses will always 
 come in useful during these operations; it should be the 
 aim of the student to be cleanly in his manipulations, and 
 endeavour to procure the best results with the minimum 
 expenditure of material. 
 
 Mounting insects without pressure has been much prac- 
 tised of late, and the splendid preparations of Mr. F. Knock 
 cannot be passed by unnoticed. A method of doing this 
 may be found as follows : Let us take the head of the 
 Dytiscus marginalis. Soak it for two days in equal parts 
 of spirits of wine and water, after which transfer it to 
 absolute alcohol for two or three days longer ; now transfer 
 it to turpentine and place it in the light until fairly bleached, 
 take it out of the turpentine and place in benzol until all 
 the former has been eliminated. Now choose a cell just 
 deep enough to hold it, glass or pure tin preferred (by no 
 means must it be of brass, this metal being acted upon 
 by balsam), rinse it out quickly with benzol, insert the head 
 and pour in some balsam just rendered thin enough to run, 
 with benzol, until the cell is full, now put on the cover, 
 cleanse the edge of the cover with a brush dipped in benzol 
 or spirits of wine, and set aside in a warm place that the 
 benzol may escape and become hardened round the edge of 
 the cover. When fairly dry give a good coat of guaiacum 
 varnish (see Recipes), and when this is dry repeat the 
 coating. Finally finish the slide with a ring of asphalte, 
 or black guaiacum varnish. 
 
 MOUNTING IN AQUEOUS MEDIA. This style of mount- 
 ing comprises the fluids and semi-fluids or viscid media ; 
 perhaps the latter are the easier done, but for sake of order 
 an illustration of how to mount starches in carbolised water 
 (see Recipes) will teach the method. 
 
304 PRACTICAL MICROSCOPY. 
 
 A suitable cell must first be selected, one of brown 
 varnish in this instance, and filled with the carbolised water 
 just made milky with the starch. The thin glass cover 
 having been taken up on the end of a pencil as already 
 described when mounting diatoms by the dry method, is 
 edged with brown varnish, allowed a few minutes to nearly 
 set, and then placed in contact with the cell but not pressed 
 down in the centre to any extent. The superfluous fluid 
 may then be absorbed with blotting paper, the slide placed 
 on the turntable, and another coat of brown varnish applied 
 to the edges. Put aside now for a day or more, and then 
 finish with white zinc varnish or asphaltum according to the 
 taste of the operator. 
 
 If the student possesses an air-pump he will find that fluid 
 mounts will be rendered more permanent by placing the 
 cell filled with fluid under the receiver so as to eliminate 
 the air which most liquids contain. The best form of air- 
 pump has been shown at Fig. 222, but there are other forms 
 which, though not so generally useful, are nevertheless 
 handy on account of their small size. One of these is 
 
 shown in Fig. 249, from which it 
 will be seen that it is capable of 
 taking slides only. 
 
 Many other fluids may be used 
 
 in place of the carbolised water: 
 FIG. 249. 
 
 the cuticle of esparto grass is 
 
 shown very well when mounted in dilute acetic acid, the 
 fibres of jute exhibit the ladder-like markings to perfection 
 when put up in dilute spirit, whfle many of the desmids 
 and minute algae can only be kept in distilled water in 
 which a lump of camphor is kept. Some of the smaller 
 organisms may be put up in a very dilute solution of osmic 
 acid. This plan is advised by Mr. Saville Kent for the 
 preservation of the collared monads, in his ' Manual of the 
 
MOUNTING INFUSORIA. 
 
 305 
 
 Infusoria/ such as the Monosiga Steinii and Salpingceca con- 
 vallaria, shown in Fig. 250. He states that they may be 
 sealed up after treatment with osmic acid without the addi- 
 
 FIG. 250. 
 
 tion of any other preservative, and that it will be found the 
 smaller and most delicate flagelliferous species are equally 
 amenable to this treatment, preserving their flagella, and 
 even, in the case of the Choano-Flagellata, their sarcode 
 collars in a life-like form. Many fluids have been described 
 for these purposes, some will be given in the recipes at 
 the end of the book, but the beginner should remember 
 never to use a fluid in a cell unless he is thoroughly 
 acquainted with the action the fluid has, or has not, upon its 
 walls or on the cements or varnishes used in connection 
 with it. If these points were more studied, fluid mounts 
 would not be looked upon with so much ill-favour as they 
 are now. 
 
 Objects mounted in glycerine should always be put in a 
 cell, and if the cover be put on in the manner described for 
 mounting in carbolised water, and diatoms, dry, the slip can 
 be easily cleaned from any superfluous glycerine. After 
 this, put the slide on the turntable, and describe a neat ring 
 of brown varnish, finally finishing with a broad ring of 
 white zinc varnish, as before described. 
 
 x 
 
306 PRACTICAL MICROSCOPY. 
 
 Objects for mounting in glycerine, such as a portion of 
 muscle with Trichinae in situ (Fig. 251), should be soaked 
 for some time in a mixture of equal parts of water, alcohol, 
 and glycerine, then exposed to the air under a bell-jar, or 
 in the desiccator ; the tissues gradu- 
 ally become filled with strong glycer- 
 ine, and the object is then ready for 
 mounting in that medium. 
 
 Turning now to viscid media, 
 the author has made much use of 
 Farrant's medium, having mounted 
 mosses and starches very successfully 
 in it. It is a very convenient sub- 
 stance, seeing that it is used cold, 
 FIG. 251. 
 
 and the slide cleaned with water 
 and a camel's-hair brush immediately after mounting ; 
 when on the following day the cover may be finished with 
 white zinc varnish and the usual coloured rings. 
 
 The next description of mounting, that in glycerine jelly, 
 is one which, to a beginner, is frequently a stumbling-block. 
 It is an exceedingly convenient method to adopt when the 
 object would be rendered too transparent in balsam or 
 dammar, or when it is undesirable to dry it at all. 
 
 In the preparation of the many things from the vegetable 
 kingdom, as mosses, algae, cuticles, and sections, and from 
 the animal kingdom, as many eyes and wings of insects, 
 gastric teeth, palates of the Mollusca, it is only necessary, 
 if they are sufficiently clean and not too dark in colour, to 
 put them for a few hours into a mixture of methylated 
 spirit, glycerine, and water (about equal parts of each), 
 although exactness is not necessary, as the mixture may 
 be varied to suit circumstances. 
 
 When they are taken from this mixture, they must be 
 placed upon the centre of the slide, and the surplus fluid 
 
MOUNTING IN GLYCERINE JELLY. 37 
 
 absorbed by blotting-paper. Either of the two plans may 
 now be followed with regard to the jelly it may be liquefied 
 by placing the bottle in hot water, and then dropping the 
 liquid jelly upon the slide, or a small piece may be cut 
 from the bottle and put upon the object and the slide 
 gently warmed, when the jelly will diffuse itself through 
 the object, and will be found exceptionally free from air- 
 bubbles ; but should there be air-bubbles or not, it is of 
 great value to boil the jelly and object upon the slide, but 
 care must be used or the mount may be ruined. Should 
 the boiling be decided upon, the clip should be used, and 
 the slide held over the flame of a lamp ; it will at first begin 
 to bubble from the centre outwards, and if the slide be 
 carefully watched, a very perceptible crack may be seen 
 and heard : at this moment, and without delay, the slide 
 must be withdrawn from the heat and placed upon a cold 
 surface (an iron slab for instance), when the jelly will 
 rapidly set and air-bubbles be excluded. 
 
 The mounts are easily cleaned from superfluous jelly, by 
 brushing with a soft tooth-brush under a running water tap, 
 the surface of the slide being allowed to dry spontaneously. 
 It will be found that the slide is free from glycerine smears, 
 which interfere much with the after-process of finishing. 
 
 FIG. 252. 
 
 The slides may then be finished by ringing with white 
 zinc varnish and the various coloured circles. 
 
 Such is the method employed for mounting in glycerine 
 
 X 2 
 
308 
 
 PRACTICAL MICROSCOPY. 
 
 jelly, and very satisfactorily illustrates the general prac- 
 tice, though of course it is not all objects which will bear 
 boiling. 
 
 An instrument called Smith's mounting machine, and 
 shown in Fig. 252, is very useful when mounting large and 
 elastic substances in glycerine jelly, as by it any degree of 
 pressure may be exerted upon the covering glass. 
 
 The method of using this instrument may be explained by 
 mounting a lichen section (Figs. 253 or 254) in Deane's 
 
 medium. The section having 
 been cut as thinly as possible, 
 it is to be soaked for a day 
 or more in some of the me- 
 dium diluted with just enough 
 water to render it fluid ; it is 
 then to be placed upon a 
 slip, the cover superposed and 
 
 FIG. 253. 
 
 FIG. 254. 
 
 placed in the mounting instrument, a gentle pressure 
 being exerted by means of the screw ; the slide must 
 now be warmed over the lamp, and a drop of the medium 
 placed at the edge of the cover, when it will be drawn 
 under by capillary attraction. This is a very clean 
 
INTELLIGENCE IN PREPARING. 
 
 309 
 
 way of mounting specimens, and one often used by the 
 author. 
 
 The foregoing instructions have been given more as an 
 aid to the student than to the expert mounter. It would 
 be impossible to give processes for mounting everything, as 
 even the preparation varies in nearly every specimen. All 
 that has been said to enable the beginner to practise the 
 art of mounting has been written in a general sense, and 
 each process must be carried out with intelligence. The 
 student should endeavour to make his preparations look as 
 natural as possible, and no pains should be spared in this 
 respect. Again, the question of varnishes and cements is 
 one which demands careful study, and the beginner is 
 advised to well peruse Chapter XIV. before he commences 
 actual work. 
 
 FIG. 255. 
 
 When the slides are mounted, a cabinet is required to 
 keep them in. They are generally made to one pattern, and 
 may be obtained from any dealer in microscopical apparatus. 
 A special and cheap form of slide box was devised some 
 years ago by Mr. Stokes. It is shown in Fig. 255, and it 
 
3io 
 
 PRACTICAL MICROSCOPY. 
 
 may be observed that the labels upon the slides are readily 
 seen without the trouble of taking out each tray. 
 
 In special methods of microscopical research there will be 
 wanting many fine and delicate pieces of apparatus, which 
 ofttimes will have to be made and devised by the student 
 himself. This is excellent practice, and he should learn to 
 exercise his ingenuity to the utmost, and not be running to 
 the optician constantly for every trifling little thing he 
 requires. An instance of how apparatus may be improvised 
 is shown by Fig. 256, which is a breeding cage for Podura, 
 
 FIG. 256. 
 
 devised and illustrated in the ' Monthly Microscopical 
 Journal ' by Mr. Mclntire. The glass plate, perforated with 
 a hole, is covered on each side with a thinner glass, and 
 held in position by two indiarubber bands. This is very 
 useful when the scales of these insects are required, and it 
 may also be brought into use as a flea cage, and for many 
 other purposes. 
 
 FIG. 257. 
 
 In concluding this chapter a few words may be said upon 
 sending slides by post. Pack them in a small wooden box 
 
SENDING SLIDES B Y POST. 3 1 1 
 
 to be obtained of any optician, tie it securely with fine 
 string and pack in a black paper wrapper. Attach a 
 luggage label to one end, upon which is to be written the 
 full address, and upon it place the postage stamps. No 
 writing of any kind should be put upon the box itself in 
 order that it may reach its destination in safety. The whole 
 when ready for the post should appear as in Fig. 257. 
 
CHAPTER XIV. 
 
 REAGENTS RECIPES. 
 
 LITTLE now remains but to notice the action and pro- 
 perties of some of the various reagents used for micro- 
 scopical purposes, and in order to put them in something 
 like order, they are divided into four classes softening 
 agents, dehydrating and hardening agents, bleaching and 
 oxidising agents, and solvents. 
 
 Softening Agents. One of the mildest softening agents 
 with which the microscopist has to deal is acetic acid 
 diluted with four times its weight of water ; it renders some 
 tissues quite transparent, and used in conjunction with 
 glycerine serves for sending insects for dissection to long 
 distances. Acetic acid dissolves phosphate and carbonate 
 of lime, but does not dissolve oxalate of lime, and neither 
 has it any action in the diluted state upon any of the 
 varnishes or cements in the general use of the microscopist. 
 
 Glycerine is a fluid of the greatest use in microscopical 
 research, particularly as an agent for preventing the drying 
 up of tissues. One part of pure glycerine diluted with 
 nine parts of water produces a fluid of the same density as 
 sea-water, and this strength is a very handy one to use. 
 Contrary to the general opinion, cells filled with glycerine 
 do not necessarily leak, it is only when objects have been 
 slovenly mounted in this medium that such a mishap 
 occurs. 
 
 The alkalies, potash, soda, and ammonia, are somewhat 
 alike in their action upon many substances, ammonia being 
 
DEHYDRA TING A GENTS. 3 1 3 
 
 the weakest reagent. When used in concentrated solu- 
 tion, animal substances, especially of an albuminoid nature, 
 are entirely dissolved, while when used in a weaker form 
 many organs are separated in such a way as to be readily 
 obtained. Upon vegetable substances the alkalies act 
 somewhat similarly, the leaf the esparto grass (Macrochloa 
 tenacissimd) and the straw of cereals, and even blocks of 
 pine wood, are all softened and disintegrated by boiling in 
 a solution of caustic soda containing 50 grains to the 
 ounce of water. Dilute nitric acid (one part of acid to ten 
 of water) may also be used as a softening agent in certain 
 cases, and, it may be added, should be used in glass or 
 porcelain vessels, as metals are rapidly dissolved by this 
 acid. This remark applies also, though in a lesser degree, 
 to acetic acid. 
 
 Dehydrating and Hardening Agents. D ehy drating agents 
 for use with the desiccator (Fig. 238) are not put in con- 
 tact with the preparation ; but placed below in a separate 
 compartment underneath a bell-jar, as shown in the figure. 
 Anhydrous phosphoric acid is perhaps the most powerful 
 absorbent we have, and next to this in usefulness is con- 
 centrated oil of vitriol. 
 
 Fluids, however, are not so handy as solids, and there, 
 fore for general work fused chloride of calcium, quick-lime, 
 or carbonate of potash, are more generally used. 
 
 When, however, a substance requires to be dried or 
 dehydrated without losing its fresh or moist appearance, 
 it must be brought in contact with a water-absorber, such 
 as alcohol. Absolute alcohol is an excellent fluid for this 
 purpose, and is not equalled by any other reagent ; methy- 
 lated spirit is often used in its place, and for many 
 purposes will suit admirably. 
 
 It must not be forgotten that alcohol has a more or less 
 solvent action upon most of the gums used for micro- 
 
PRACTICAL MICROSCOPY. 
 
 scopical varnish making, and therefore strong alcohol 
 cannot be used in such cells. Weak spirit has, however, 
 no action upon a cell of gold size, and this is the only 
 varnish the author advises to be used when an object is 
 mounted in weak spirit. 
 
 As to hardening agents, the chromates have been treated 
 of in Chapter VIII. on Section-cutting, and therefore it is 
 not necessary to recapitulate their uses. 
 
 Tannin dissolved either in water or alcohol is a harden- 
 ing agent especially useful for gelatinous tissues ; it is used 
 sometimes in injecting for hardening the walls of blood- 
 vessels to prevent the passage of the coloured gelatine 
 through them. Alcohol itself is a very powerful but safe 
 hardening agent, and when combined with tannin may find 
 many uses. 
 
 Bichloride of mercury solution has been recommended 
 as a hardening agent, and it probably acts by forming 
 insoluble compounds with the albuminoid matters. It is 
 so deadly a poison that the author can scarcely advise the 
 student to use it. 
 
 Osmic acid, easily purchased in a one per cent, solution, 
 is also a splendid hardening agent, and is of great use in 
 studying the lower forms with naked protoplasm. It is, 
 however, very poisonous. By the action of this reagent the 
 currents in the protoplasm of Myxomycetes are instantly 
 suspended, and in a few moments the plasmodium is suffi- 
 ciently hardened to make sections possible. 
 
 Bleaching and Oxidising Agents. Under this class we 
 have : 
 
 Chlorinated soda (eau Labarraque), 
 
 Chloride of lime (bleaching powder), 
 
 Chlorate of potash, 
 
 Bichromate of potash, 
 
 Nitric acid, 
 
 Turpentine, 
 
 all of which have their special uses. 
 
BLEA CHING AND OXIDISING A GENTS. 3 1 5 
 
 The first two are principally used for bleaching vegetable 
 sections, and the strength of the solution may be found in 
 the Receipts at the end of the book. It is most important, 
 when using these reagents, to eliminate every trace of them 
 after the operation is finished, and this may be done by 
 soaking in a bath of neutral sulphite of soda, 15 grains to 
 the ounce of water ; a solution of one part of strong liquid 
 ammonia to twenty parts of water will also effect this. 
 
 Chlorate of potash is generally used for cleaning diatoms, 
 in connection with some strong acid such as sulphuric, nitric, 
 or hydrochloric. Great care should be used in making these 
 mixtures, as it is easy with them to produce explosions, 
 and their use should (in connection with chlorate of potash) 
 be avoided as much as possible. Nitric acid by itself is a 
 powerful bleacher and oxidiser, but has the disadvantage of 
 emitting powerfully noxious and acid fumes ; when slightly 
 diluted to prevent this, its oxidising powers can be increased 
 by the addition of chromic acid or bichromate of potash. 
 This admixture is not in the least likely to explode. 
 
 Another extremely powerful oxidiser is a mixture of 
 strong sulphuric acid and chromic acid in crystals ; it is 
 especially useful in cleansing diatoms, and must be heated 
 carefully over the spirit-lamp to obtain its maximum effect. 
 Peroxide of hydrogen is an extremely valuable bleaching 
 agent and oxidiser, and likely to come into general use 
 when its properties are better known to microscopists ; it is 
 neither acid nor alkaline, and does not give off any objec- 
 tionable odour. Another bleaching agent is turpentine, 
 almost exclusively used to reduce the intensity of colour in 
 the chitinous skeletons of insects. After having been treated 
 with potash or soda solution, and the abdominal contents 
 expressed, the insect is washed with water, dried in alcohol, 
 and allowed to soak in turpentine until the colour of the 
 chitin is sufficiently reduced in intensity. Turpentine has 
 
PRACTICAL MICROSCOPY. 
 
 a solvent action upon many of the varnishes used for 
 microscopical purposes, and therefore great caution should 
 be exercised in this respect. 
 
 Solvents. Under this heading come many reagents of 
 diverse character : we have alkalis, acids, and neutral com- 
 pounds, all of which have their special applications. Amongst 
 the first class are solutions of potash, soda, and ammonia, 
 having a great affinity for most animal substances. Grease 
 unites with any of these, producing a soap which easily 
 dissolves in water. The alkalis in their solid state should 
 be handled with caution, owing to their corrosive nature ; 
 they are chiefly used in solution to dissolve out the internal 
 organs of insects, and to prepare the leaves of mosses for 
 exhaustive scientific examination. 
 
 The acids, sulphuric, nitric, hydrochloric, and acetic, 
 have each their uses ; for dissolving metals, oxides, car- 
 bonates, phosphates, and other salts, they are necessary. 
 They have no action upon silica, but upon animal and 
 vegetable fibres the action is very decided. 
 
 By far the most important solvents we have to consider 
 are ether, alcohol, benzol, glycerine, oil of cloves, oil of caje- 
 put, and last, and not least, water. Ether is not very 
 soluble in water, it dissolves in about fourteen parts at the 
 ordinary temperature of the air ; it carries into solution 
 many organic compounds, as the volatile oils, resins, fats, 
 alcohols, tannic acid, which are but sparingly soluble in 
 alcohol, while it is without action upon many substances 
 easily dissolved by that reagent. It is miscible in all pro- 
 portions with alcohol, bisulphide of carbon, and naphtha. 
 
 Alcohol is probably the most used fluid in microscopy ; 
 it is miscible in all proportions with wood-spirit, chloro- 
 form, acetic acid, and naphtha, and is a good solvent for 
 most resinous substances. Attention should be paid to 
 the strength of the alcohol ; alcohol absolute is expensive, 
 
SOLVENTS. 317 
 
 and though a good drier, sometimes fails in its action 
 because it is too strong. Ordinary druggists' alcohol of 
 85 per cent, is an excellent solvent for resins, camphor, 
 tannin, the balsams, iodine, acetic acid, and castor oil, but 
 the ordinary " spirits of wine," consisting of equal volumes 
 of druggists' alcohol and water, has not the same solvent 
 action for resinous matters. Methylated spirit consists of 
 ordinary alcohol, mixed with 10 per cent, of wood-spirit, 
 and is capable of being put to the use of ordinary alcohol 
 by the microscopist. 
 
 Benzol is a colourless, strongly refracting liquid, of a 
 very inflammable nature. It is almost insoluble in water, 
 but dissolves freely in alcohol and ether. It dissolves 
 iodine, sulphur, fats, gum-resins, and many other com- 
 pounds, such as caoutchouc and guttapercha. 
 
 Petroleum naphtha, called also benzoline, benzine, gaso- 
 line, &c., is nearly as useful as coal-tar benzol for the 
 purposes of the microscopist, provided it be of good quality 
 and does not contain any quantity of heavy oils. 
 
 Glycerine is a solvent strongly recommended for general 
 use by Dr. Beale. It is soluble in all proportions in water 
 and alcohol, though it is but sparingly soluble in ether. 
 It dissolves nearly all organic substances soluble in water, 
 and many of those soluble in alcohol ; it dissolves small 
 quantities of carbonate of lime and many oxides ; 20 per 
 cent, of arsenious acid, and 10 per cent, of tannic acid, form- 
 ing with this latter a waxy solid, melting at the temperature 
 of the body, which the author has used sometimes for 
 mounting purposes. 
 
 Oil of cloves is often used as an intermediate bath 
 between alcohol and Canada balsam ; it serves to take out 
 the alcohol, with which the oil changes place. One volume 
 of oil of cloves dissolves an equal volume of alcohol. 
 
 Oil of cajeput is often recommended for use in place of 
 
3 1 8 PR A CTICAL MICROSCOP Y. 
 
 oil of cloves, and is in every way cheaper, as one volume of 
 it absorbs eleven volumes of alcohol, or is eleven times 
 more efficient than oil of cloves. 
 
 And now we must consider water, perhaps the most 
 useful solvent we have. A great many substances are 
 soluble in this fluid, and even those generally considered 
 insoluble are acted upon to such an extent as to interfere 
 with it for microscopical purposes. Air, or rather the 
 oxygen and nitrogen of the air, are soluble in water, and 
 cause the microscopist no little trouble. This has been 
 dealt with on page 304, and it may also be stated that 
 when water is to be evaporated on a slide for future 
 mounting, the water should be distilled, so that no 
 objectionable residue is left. 
 
 RECIPES. 
 
 CARBOLIC ACID (Fluid). 
 
 Procure an ounce bottle of Calvert's pure crystallised carbolic acid, place it 
 in a jar of warm water to melt ; then add two drachms of methylated spirit, 
 mix, and preserve for use. 
 
 If strong carbolic acid be spilled upon the hands, it must be immediately 
 wiped off with oil, not water. 
 
 CARBOLIC ACID WATER. 
 Strong. 
 
 Fluid carbolic acid I drachm. 
 
 Distilled water 16 oz. 
 
 Weak. 
 
 Carbolic acid water (strong) i oz. 
 
 Distilled water . . . . 9 oz. 
 
 CHLORINATED SODA (solution}. 
 
 Dry chloride of lime 2 oz. 
 
 Soda crystals (washing soda) 3 oz. 
 
 Water 2 pints. 
 
 Mix the chloride of lime with half the water, and the soda in the other half, 
 mix the whole together, and allow to settle in a well-corked bottle. Pour off 
 the clear liquid for use, which must be kept in a well-corked bottle. 
 
RECIPES. 319 
 
 CHLORINATED LIME (solution). 
 
 Dry chloride of lime \ oz. 
 
 Water I quart. 
 
 Dissolve and allow to settle. 
 
 LIQUOR POTASS^E (solution]. 
 
 Caustic potash (in sticks) 2 oz. 
 
 Water I quart. 
 
 Caustic soda may be substituted for the potash. 
 
 IODINE SOLUTION. 
 
 Iodine 40 grains. 
 
 Iodide of potassium 60 grains. 
 
 Water I pint. 
 
 Dissolve the two substances in four ounces of the water, then add the 
 remainder. 
 
 GUM WATER. 
 
 Gum arabic 4 oz. 
 
 Glycerine oz. 
 
 Weak carbolic acid water 4 oz. 
 
 Allow to stand in the cold until dissolved. 
 This will be found an excellent medium for attaching labels to glass. 
 
 SPICER'S FLUID. 
 
 Alcohol .. 3 flui^oz. 
 
 Distilled water 2 fluid oz. 
 
 Glycerine I fluid oz. 
 
 GOADBY'S FLUID, No. i. 
 
 Bay salt 4 oz. 
 
 Alum 2 oz. 
 
 Corrosive sublimate 4 grains. 
 
 Water 2 quarts. 
 
 Dissolve and filter, when it will be ready for use. 
 
 GOADBY'S FLUID, No. 2. 
 
 Bay salt 8 oz. 
 
 Corrosive sublimate 2 grains. 
 
 Water I qua rt. 
 
 CAMPHOR WATER. 
 
 Distilled water , I quart. 
 
 Tincture of camphor I drachm. 
 
 Well mix, but use only the clear fluid. 
 
320 PRACTICAL MICROSCOPY. 
 
 THWAITES' FLUID. 
 
 Rectified spirit i oz. 
 
 Creosote (wood) .. .. q. s. 
 
 Distilled water I pint. 
 
 Precipitated chalk q. s. 
 
 Saturate the spirit with creosote, then add the water and a little precipitated 
 chalk. Filter, when the liquid is ready for use. 
 
 RALF'S LIQUID. 
 
 Bay salt I grain. 
 
 Alum i grain. 
 
 Distilled water I oz. 
 
 GLYCERINE AND ACETIC ACID. 
 
 Glycerine 2 oz. 
 
 Glacial acetic acid \ oz. 
 
 GLYCERINE AND GUM. 
 (Farranfs Medium?) 
 
 Gum arabic 4 oz. 
 
 Distilled water 4 oz. 
 
 Glycerine 2 oz. 
 
 Dissolve in the cold. 
 
 DEANE'S MEDIUM. 
 
 Nelson's gelatine I oz. 
 
 Honey 5 oz. 
 
 Creosote 6 drops. 
 
 Alcohol ^ oz. 
 
 Water 5 oz. 
 
 Soak the gelatine in 4 oz. of the water for twelve hours, add the honey, pre- 
 viously heated to nearly boiling point, in a separate vessel, and boil the whole 
 together. When cooled somewhat, add the spirit and water in which the 
 creosote has been dissolved. Afterwards, filter through fine flannel. 
 
 GLYCERINE JELLY (Lawrance's). 
 
 Gelatine I oz. 
 
 Glycerine 6 drachms. 
 
 Camphorated spirit of wine J oz. 
 
 Cover the gelatine with cold water, and allow it to soak until it becomes 
 soft. Dissolve by placing the jar containing it in a vessel of boiling water, 
 and allow it to cool, then add a small quantity of the white of an egg, and boil 
 the mixture until the albumen coagulates, when the whole is to be filtered 
 through fine flannel, and mixed with the glycerine and spirit. 
 
RECIPES. 321 
 
 LIQUID GLUE. 
 
 Dissolve shellac in wood-naphtha at a very low temperature, until the 
 mixture is of the required consistency. 
 
 It makes a very brittle varnish, but very good cells. 
 
 BROWN VARNISH. 
 
 Pure indiarubber 20 grains. 
 
 Bisulphide of carbon q. s. 
 
 Shellac 2 oz. 
 
 Methylated spirit 8 oz. 
 
 Dissolve the indiarubber in the smallest possible quantity of bisulphide of 
 carbon, and add this to the alcohol in such a manner that the whole is mixed 
 without the formation of clots. Now add the shellac, and place the jar con- 
 taining the mixture in boiling water, until the whole of the shellac is dissolved, 
 and the smell of the bisulphide has disappeared. 
 
 GUAIACUM VARNISH. 
 
 Gumguaiacum 2 oz. 
 
 Shellac 2 oz. 
 
 Methylated spirit 10 oz. 
 
 Powder the guaiacum and dissolve it in the spirit, filter, and then add the 
 shellac. Keep the whole in a jar surrounded by warm water until dissolved. 
 
 MATT VARNISH. 
 
 Gum mastic 40 grains. 
 
 Gumsandarac 1 60 grains. 
 
 Methylated ether 4 oz. 
 
 Benzol i| oz. 
 
 BLACK MATT VARNISH. 
 
 Gum mastic 50 grains. 
 
 Gum sandarac 200 grains. 
 
 Methylated ether ij oz. 
 
 Benzol oz. 
 
 Dissolve the gums in the fluids and triturate in a mortar with sufficient lamp- 
 black of the finest quality. 
 
 MARINE GLUE. 
 
 Indiarubber shreds 202. 
 
 Shellac 20?. 
 
 Dissolve the indiarubber in solvent mineral naphtha, add the shellac in 
 powder, and heat until liquefied, well mixing the whole together. It produces 
 a solid marine glue, and requires heat in its application. The author has it on 
 good authority that very little of the marine glue at present made contains a 
 particle of indiarubber. 
 
 Y 
 
322 PRACTICAL MICROSCOPY. 
 
 PHOTOGRAPHIC VARNISH (for negatives], 
 
 Gum benzoin oz. 
 
 Gum sandarac I oz. 
 
 Methylated spirit 12 oz. 
 
 FRENCH POLISH. 
 
 Shellac 3 oz. 
 
 Gum sandarac \ oz. 
 
 Methylated spirit . . I pint. 
 
 French polish is sometimes coloured with gum dragon, &c. 
 
 BRUNSWICK BLACK or BLACK JAPAN. 
 
 Egyptian asphaltum 4 oz. 
 
 Linseed oil 4 oz. 
 
 Boil together for some time, and mix to the required consistency with oil of 
 turpentine. 
 
 CANADA BALSAM VARNISH 
 (For rendering ground glass transparent). 
 
 Take 4 oz. of Canada balsam, and bake in a cool oven till quite brittle when 
 cooled. Dissolve this in 12 oz. of benzol, in which \ oz. of mastic has been 
 previously dissolved. 
 
 BLACK VARNISH (Davies). 
 
 Indiarubber shreds 30 grains. 
 
 Egyptian asphaltum . . . . 4 oz. 
 
 Solvent naphtha (mineral) 10 oz. 
 
 Dissolve the indiarubber in the naphtha, add the asphaltum, using heat if 
 necessary. 
 
 BALSAM AND BENZOL. 
 
 Bake the Canada balsam in a cool oven, and then dissolve to the right con- 
 sistency with benzol. If baked too long the residue will be too brittle ; if too 
 short, it will not dry quickly enough. 
 
 DAMMAR AND BENZOL. 
 
 Gum dammar . . . . I oz. 
 
 Benzol 2 oz. 
 
 MASTIC AND BENZOL. 
 
 Gum mastic 4 oz. 
 
 Benzol 3 oz. 
 
RECIPES. 323 
 
 GOLD SIZE. 
 
 Linseed oil 25 oz. 
 
 Red-lead I oz. 
 
 Powdered white-lead 
 
 Yellow ochre 
 
 Boil the oil and red-lead together for about three hours, taking care it does 
 not burn or boil over ; pour off the clear fluid, and boil again with a mixture 
 of equal parts of the white-lead and yellow ochre, added in small successive 
 portions. Pour off the clear fluid for use. 
 
 BLACK GOLD SIZE. 
 
 Triturate in a mortar I fluid oz. of gold size with sufficient lampblack to 
 form a dense black colour. If too thick, it may be thinned with a little 
 turpentine. 
 
 FINISHING VARNISHES 
 (For white and coloured rings). 
 
 These are made by triturating the various colours with the vehicle in a 
 mortar. It will be found best, after preparing each colour, to place them in 
 saucers such as are used by artists ; the benzol then evaporates, and the colour 
 can be taken up in a brush, as required, by simply moistening it with benzol. 
 
 The vehicle : 
 
 Gum dammar 3 oz. 
 
 Gum mastic I oz,_ 
 
 Benzol 6 oz. 
 
 The colours : 
 
 White oxide of zinc. 
 
 Blue ultramarine. 
 
 Red carmine. 
 
 Black lampblack. 
 
 Green verdigris. 
 
 Yellow chrome-yellow. 
 
 The foregoing formulae are given in order that micro- 
 scopists may, when desirable, be able to compound them 
 for themselves. The author is of the opinion, however, 
 that it will be found cheaper, where only small quantities 
 are required, to purchase from a dealer in microscopical 
 sundries, as most of these articles can only be satisfactorily 
 made in large quantities. On the other hand, he would 
 
 Y 2 
 
324 PRACTICAL MICROSCOPY. 
 
 also advise that the dealers in " secret nostrums " be not 
 encouraged, for it is generally found that the greater the 
 so-called secret, the more quackery there is about it, and 
 the less utility. 
 
INDEX. 
 
 A. 
 
 ABBE'S researches, 1 14 
 
 apertometer, 235 
 
 Absorption bands, 253 
 
 Acarus domesticus, 135 
 
 farinse, 135 
 
 Accessories, 58 
 
 Accommodation depth of eye, 114 
 
 Acetic acid, 312 
 
 and glycerine, 320 
 
 Acheta domestica, 170 
 
 Acremonium alternatum, 144 
 
 Actinic and visual foci, 210 
 
 correction for, 212 
 
 Actinozoa, 160 
 
 Adiantum capillus Veneris, 142 
 
 Adjustment of covering glass, 112 
 
 >Esculus hippocastanum, 108 
 
 Air-pump, 260, 304 
 
 Air-bubbles, elimination of, 304, 307 
 
 Alcohol, 313, 316 
 
 Algse, 132, 272 
 Alkalies, 312 
 
 Althea rosse, pollen of, 107 
 Alum bath for negatives, 223 
 American clips, 298 
 
 oculars, 43 v 
 
 Amici prism, 72 
 Ammonia, 313 
 
 picrate of, 264 
 
 Ammonio-sulphate of copper, 96, 216 
 
 spectrum of, 253 
 
 Amphipleura pellucida, 103, 118 
 
 photographing, 220 
 
 Amphiprora alata, 141 
 Amplifying power of objectives, 53 
 Analysing prism, 239 
 
 for eye-piece, 240 
 
 Animalcules, 133 
 
 Animal sections, staining, 265 
 
 tissues, hardening, 191 
 
 preparing, 190 
 
 section-cutting, 193 
 
 Anuraea longispina, 134 
 Apertometer, Abbe's, 234 
 Apertures, measuring, 56, 234 
 
 numerical, 125 
 
 'Table of, 126 
 
 value of wide, 123 
 
 Aplanatic lenses, 106 
 
 Apparatus for collecting mosses, 154 
 
 Arachnida, 135 
 
 Arachnoidiscus Ehrenbergii, 140 
 
 Aregma bulbosum, 144 
 
 Argulus foliaceus, 136 
 
 Arranged slides of Diatoms, 291, 294 
 
 Foraminifera, 294 
 
 Polycistina, 294 
 
 Artificial star test, 102 
 Asellus vulgaris, 136 
 Aspergillus alternatus, 144 
 
 glaucus, 144 
 
 Astromma Aristotelis, 155 
 Athyrium filix fsemina, 142 
 
 BACILLARIA PARADOXA, 141 
 Baker's treatise on the Microscope, 2 
 Balsam angles, 123 
 
 and benzol, 322 
 
 mounting in, 299 
 
 mounting in, 297 
 
 Bangia fuscopurpurea, 133, 272 
 Barbadoes rock, 151 
 Beck's "Economic Stand," 36 
 "International," 14 
 
 vertical illuminator, 75 
 
 Bedding agents, 188 
 
326 
 
 INDEX. 
 
 Bench for mineral sections, 195 
 Benzol, 317 
 
 and balsam, 322 
 
 and dammar, 322 
 
 and mastic, 322 
 
 Benzoline, 317 
 
 Biaxial crystals, rings in, 246 
 
 Bichloride of mercury, 314 
 
 Bichromates, 314 
 
 Binocular eye-piece, Tolles', 33 
 
 microscope, Stephenson's, 33 
 
 prism, Wenham's, 32 
 
 , high power, 33 
 
 Powell and Lealands, 33 
 
 Bioplasm staining, 267 
 Black japan, 322 
 
 ringing varnish, 323 
 
 varnish (Davies), 322 
 
 Bleaching agents, 314 
 
 in turpentine, 299 
 
 Blood, spectra of, 253 
 Blow-fly, dissecting, 171 
 internal organs of, 172 
 
 proboscis of, 108 
 
 Blue ringing varnish, 323 
 Bone, cutting sections of, 201 
 Bosmina longirostris, 136 
 Botterill's life-slide, 87 
 
 trough, 87 
 
 Bright spot micrometer, 256 
 Browning's pocket microscope, 140 
 
 portable microscope, 22, 23 
 
 " rotating stand, 21 
 Brown's pocket microscope, 139 
 Brown varnish, 321 
 
 cells, 284 
 
 Brunswick black, 322 
 Brushes, 167 
 Bulloch's stand, 25 
 Bull's-eye condenser, 61, 101 
 
 C. 
 
 CAGE for Podura, 310 
 Cajeput, oil of, 317 
 Calotte diaphragm, 64 
 Cambium staining, 259 
 Camel-hair brushes, 167 
 Camera lucida, 205 
 Nachet's, 207 
 
 Camera lucida, Swift's, 207 
 
 photomicrographic, 208 
 
 Camphor water, 319 
 
 Canada balsam varnish, 322 
 
 Cape Lory, colouring matter from, 253 
 
 Carbolic acid, 318 
 
 water, 318 
 
 Cardboard cells, 284 
 Carmine staining, 262 
 Cells, 276, 284 
 
 ammonia-sulphate of copper, 96 
 
 built up, 285 
 
 Cell-making, 283 
 Cellular tissue, staining, 259 
 Ceramium, 133 
 Chirocephalus diaphanus, 136 
 Chlorate of potash, 314 
 Chloride of lime, 314, 319 
 
 of gold staining, 266 
 
 Chlorinated soda, 314, 318 
 Chromates, 314 
 Chromic acid, 315 
 Cladonia pyxidata, 151 
 Cladophora, 133 
 Classification of objectives, 105 
 Cleaning diatoms, 139, 288 
 
 mixture for glass slips, 274 
 
 oculars, 44 
 
 specimens, 286 
 
 Clips, spring, 300 
 
 whalebone, 299 
 
 Cloves, oil of, 317 
 
 Coal, cutting sections of, 200 
 
 Coddington lens, 5 
 
 Codosiga botrytis, 146 
 
 Ccencecium, 155 
 
 Coleoptera, 146 
 
 Coleosporium synantherarum, 144 
 
 Coleps hirtus, 134 
 
 Collecting apparatus for diatoms, 138 
 
 ferns, 142 
 
 case, Stanley's, 131 
 
 Collection of objects, 127 
 Collins' Harley binocular, 18 
 Collodio-albumen plates, 228 
 Coloured varnishes, 323 
 Compressors, 85 
 Concave mirrors, 98 
 Condenser, bull's-eye, 61 
 
INDEX. 
 
 327 
 
 Condenser, Collins' Webster, 66 
 
 Webster's, 65 
 
 Powell and Lealand's, 68 
 
 oil -immersion, 68 
 
 Reade's, 68 
 
 Wollaston's, 65 
 
 Swift's, 67 
 
 Condy's pink fluid, 251 
 
 Construction of objectives, 47 
 
 Convex lenses, loo 
 
 Cordylophora, 160 
 
 Cotton fibres, 302 
 
 Cover adjustment, 112 
 
 Covers, thin glass, 275 
 
 Crane fly, internal organs of larva of, 
 
 177 
 
 Cristatella mucedo, 155 
 Crouch's Premier binocular, 20 
 Crustacea, 136 
 Cuticles, mounting, 304 
 
 staining, 259 
 
 Cutting sections of animal tissues, 192 
 
 bone, 201 
 
 coal, 200 
 
 rocks, 199 
 
 teeth, 201 
 
 vegetable tissues, 189 
 
 Cyclops quadricornis, 136 
 Cydippe, 160 
 Cypris tristriata, 136 
 Cystopus candidus, 144 
 
 D. 
 DAMMAR and benzol, 322 
 
 mounting in, 301 
 
 Daphnia pulex, 136 
 Barker's selenite films, 241 
 Dark wells, 81 
 Dasya coccinea, 133, 272 
 Deane's medium, 320 
 
 mounting in, 308 
 
 Defining power of objectives, 103, 105 
 Dehydrating agents, 313 
 Delineation of objects, 203 
 
 by ruled squares, 204 
 
 Depth of focus, 1 14 
 Desiccator, 287 
 Developing negatives, 221 
 solutions, 221, 222 
 
 Diamond dust, charging slitter with, 
 
 196 
 Diaphragms, 63 
 
 Collins' graduating, 63 
 
 Dancer's aperture, 124 
 
 iris, 63 
 
 Swift's calotte, 64 
 
 Diatom illuminator, 72 
 Diatomaceae, 117, 137 
 Diatoma vulgare, 140 
 Diatoms, cleaning, 139, 288 
 
 mounting, 291, 299 
 
 arranged slides, 291, 294 
 
 separating, 290 
 
 where to find, 137 
 
 Didymium oxalate, spectrum of, 253 
 
 Diffraction, results of, 122 
 
 Diopside, rings in, 246 
 
 Dipping tubes, 130 
 
 Diptera, 146 
 
 Disc-holder, 83 
 
 Disintegration of vegetable matter, 180 
 
 Dissecting, bedding agents for, 167 
 
 knives, 168 
 
 ' microscope, Collins', 163 
 
 Houston's, 163 
 
 Lawson's, 164 
 
 Stephenson's binocular, 165 
 
 needles, 167 
 
 scissors, 169 
 
 the blow-fly, 171 
 
 the object of, 177 
 
 the use of, 181 
 
 vegetable matter, 179 
 
 Distortion, freedom from, 112 
 Dollond's experiments, 45 
 Doublets, Wollaston's, 45 
 Double-image prism, 240 
 
 nose-piece, 60 
 
 Double staining, 262 
 
 carmine and green, 262 
 
 picro-carmine, 263 
 
 wood sections, FRONTISPIECE 
 
 Draw-tube, 58 
 
 Drying preparations, 287 
 
 Dry mounting, 285 
 
 plates, 213, 228 
 
 Dytiscus marginalis, 146, 170, 172, 
 
 300 
 
328 
 
 INDEX. 
 
 EARLY objectives, Ross and Spencer, 
 
 46 
 
 Echinodermata, 141 
 Echinus spine, cutting sections of, 
 
 200 
 
 section of, 112 
 
 Electric light, 217 
 
 battery for, 218 
 
 Elimination of air from fluid mounts, 
 
 304 
 
 Engraver's lenses, 4 
 Epidermis staining, 259 
 Erector, 59 
 
 table of amplifications, 166 
 Ether, 316 
 Euchlanis dilata, 146 
 Euglena viridis, 134 
 Extraordinary ray, 238 
 Eye-pieces or oculars, 9, 40, 54 
 Eye-piece, Huyghenian, 40 
 
 Kelner's orthoscopic, 42 
 
 Ramsden's positive, 41 
 Tolles' binocular, 33 
 
 F. 
 
 FERNS, 142 
 
 collecting apparatus for, 142 
 Ferrous oxalate development, 222 
 Fine adjustment, 212 
 Finishing slides, 292 
 
 varnishes, 323 
 
 Fixing solution, 224 
 negatives, 225 
 Flatness of field, 103, 112 
 Floscularia cornuta, 146 
 Flustra foliacea, 157 
 Focus, depth of, 114 
 Focussing glass, artificial, 21 1 
 
 in photomicrography, 21 1 
 
 Foraminifera, 143 
 
 arranged slides of, 294 
 
 Forceps, dissecting, 170 
 mineral, 82 
 
 stage, 8 1 
 
 Fossil fungi, 2OI 
 Freedom from distortion, 112 
 Freezing microtome, 194 
 French polish, 322 
 
 Frog's lung, section of, 115 
 Fungi, 144 
 fossil, 201 
 
 G. 
 
 GAMMARUS PULEX, 136 
 
 Gasoline, 317 
 
 Glass crystallites, 152 
 
 slides or slips, 97, 273 
 
 rough edges, 273 
 
 with ledge, 88 
 
 Glycerine, 305, 312, 317 
 
 and acetic acid, 320 
 
 and gum, 320 
 
 Glycerine- jelly, 320 
 
 mounting objects in, 306 
 
 Goadby's fluid, 319 
 Gold size, 323 
 
 black, 323 
 
 cells, 284 
 
 Goring's treatise, 2 
 Graduating diaphragm, 63 
 Grammatophora marina, 141 
 Green ringing varnish, 323 
 Griffithsia, 133 
 Ground glass, artificial, 211 
 Guaiacum varnish, 321 
 Guano, 290 
 
 Gum and glycerine, 320 
 Gum water, 319 
 Gyrosigma angulatum, 118 
 formosum, 117 
 
 H. 
 
 HABITATS of diatoms, 137 
 Hairs, stained, 259 
 Hardening agents, 313 
 
 animal tissues, 191 
 
 Hartnack's objectives, 54 
 Heliostat, 215 
 
 Hoggan's section-cutting machine, 201 
 Hollyhock, pollen of, 107 
 Homogeneous - immersion objectives, 
 
 121 
 
 Horse-chestnut stem, section of, 108 
 Hot-air chamber, 284 
 How to collect mosses, 154 
 Human liver, section of, 115, 117 
 muscle with T. spiralis, 193 
 
INDEX. 
 
 329 
 
 Humble bee, sting of, 175 
 Huyghenian eye-piece, 41 
 Hydra viridis and fusca, 1 60 
 Hydroid Zoophytes, 160 
 Hydrozoa, 160 
 Hymenoptera, 146 
 Hyposulphite of soda solution, 224 
 
 ILLUMINATOR, Beck's vertical, 75 
 
 Osborne's, 74 
 
 Powell and Lealand's vertical, 75 
 
 reflex, Wenham's, 71 
 
 Tolles' interior, 76 
 
 traversing substage, 69 
 
 Wenham's diatom, 72 
 
 white cloud, 96 
 
 Immersion objectives, 104, 121 
 
 paraboloid, 78 
 
 Inch objectives, 51 
 Infusoria, 145 
 
 mounting, 305 
 
 Injected kidney, 192 
 
 Injecting and staining, 259, 269 
 
 apparatus, 269 
 
 fluid, carmine, 269 
 
 Prussian blue, 268 
 
 Injections, opaque, 268 
 
 transparent, 268 
 
 Insecta, 147 
 
 Insects, mounting in balsam and benzol, 
 299 
 
 ' without pressure, 303 
 
 Intensification of negatives, 224 
 Iodine solution, 319 
 Iris diaphragm, 63 
 Isthmia enervis, 140 
 
 J. 
 
 JACKSON model, the, 12 
 Jackson's eye-piece micrometer, 233 
 Japan black, 322 
 Jute fibres, mounting of, 304 
 
 K. 
 
 KELNER'S orthoscopic eye-piece, 42 
 Kidney, injected, 192 
 Klein's quartz-plate, 242, 246 
 
 Knives, 168, 187 
 
 L. 
 
 LABELS for slides, 298 
 
 Lagena squamosa, 144 
 
 Lamps, 91-95 
 
 Lantern, microscope, 229 
 
 objects for, 229 
 
 transparencies, 227 
 
 Lap, leaden, 196 
 
 Larva of crane-fly, 177 
 
 Lastrea filix mas, 142 
 
 Lathe, 197 
 
 Laticiferous vessels, 259 
 
 Leaden lap, 196 
 
 Lecanora cerina, 150 
 
 Lecidea canescens, 151 
 Lens, 4 
 
 aplanatic, 106 
 
 Coddington, 5 
 
 convex, 100 
 
 engraver's, 4 
 
 magnifying power of, 8 
 
 over-corrected, 106 
 
 plano-convex, 101 
 
 platyscopic, 5 
 
 pocket, 4 
 
 spot, 77 
 
 Stanhope, 5 
 
 Steinheil's, 5 
 
 under-corrected, 106 
 
 watchmaker's, 4 
 
 Lepidocyrtus curvicollis, in, 148 
 Lepidoptera, 146 
 Lepisma saccharina, in, 148 
 Liber- cells, staining, 259 
 Lichens, 149 
 
 sections of, 190 
 
 mounting, 308 
 
 Lieberkuhns, 79 
 
 mounting for, 296 
 
 Life-history of organisms, 3 
 
 slide, Botterill's, 87 
 
 Light, refraction of, 97 
 
 modifier, 95 
 
 monochromatic, 96 
 
 Smiting diaphragm, 124 
 Jmnias ceratophylli, 146 
 Liquid glue, 321 
 
330 
 
 INDEX. 
 
 Liquor potassoc, 319 
 Lister, J. J.'s, researches, 45 
 Live-boxes, 84 
 Liver, human section of, 115 
 Locusta viridissima, 1 70 
 Logwood solution, 260 
 
 staining, 259, 261 
 
 Lnplinpiis cry ,I:illinil>, I 56 
 
 Low-angle objectives, 106, 120 
 
 M. 
 
 MAGENTA and tannin staining, 266 
 Magnesium lamp, 218 
 Magnifying power of lenses, 8 
 Maps, microspectroscopic, 257 
 Marine glue, 321 
 
 cells, 284 
 
 Marsh's section spoon, 184 
 
 Mastic and benzol, 322 
 
 Matthews' section-cutting machine, 202 
 
 Matt varnish, 321 
 
 black, 321 
 Measuring apertures, 56, 234 
 wedge for thin glass, 275 
 Mechanical finger, 293 
 
 stage, 19 
 Melicerta ringens, 134 
 Mercury, bichloride of, 314 
 Meridion circulare, no, 140 
 Methylated spirit, 313, 317 
 Micra, 230 
 
 Micro-dissections, 162 
 Microfungi, 145 
 i. mounting, 295 
 Micrometers, 230 
 
 stage, 230 
 
 Browning's light-spot, 256 
 
 Jackson's eye-piece, 233 
 
 Ramsden's, 232 
 
 screw, 234 
 
 Micromillimetres, 231 
 Microphotographs, 112 
 Microscopes, 9-38 
 
 working, 38 
 Microscope lamps, 91-95 
 
 dissecting, 163-165 
 
 lantern, 229 
 
 petrological, 245 
 Microscopical preparations, 271 
 
 Microscopical priiiriplcs, 3 
 
 preparations, Dr. Pcllctan on, 271 
 Microscopy, old works on, 2 
 Microspectroscopc, 249 
 
 sections of, 256 
 
 Microtome, Dancer's, 185 
 free/ing, 194 
 
 Rutherford's, 185, 194 
 
 Swift's, 1 86 
 
 Minerals, 151 
 
 forceps for, 82 
 
 cutting sections of, 199 
 Mirrors, concave, 98 
 
 plane, 98 
 
 Moisture, elimination of, 288 
 Mailer's test-plate, 120 
 Mollusca, 153 
 Monochromatic light, 96 
 Monterey stone, 290 
 Morpho Menelaus, 1 10 
 Morris's rotating stage, 82 
 Mosses, 154 
 apparatus for collecting, 154 
 
 how to collect, 154 
 Mounting-board, 301 
 
 diatoms, 291, 299 
 
 dry, 285, 294 
 
 fluids, 304 
 
 in aqueous media, 285, 303 
 
 in balsam, 297 
 
 in glycerine, 305 
 
 in glycerine jelly, 307 
 
 in gum resins, 285, 296 
 
 infusoria, 304 
 
 insects without pressure, 303 
 jute fibres, 304 
 
 lichen sections, 308 
 
 microfungi, 295 
 
 objects, 271 
 
 starch-granules, 295 
 
 Muscle, human, with T. spiralis, 193 
 Muscular system of animals, 244 
 Myxomycetes, hardening protoplasm 
 of, 3'4 
 
 N. 
 
 NACHET'S prism, 74 
 Naturalist's studio, 132 
 Natural sines, Table of, 236 
 
INDEX. 
 
 331 
 
 Navicula firma, 141 
 
 lyra, 141 
 
 rhomboides, 103, 117, 118 
 Needles, dissecting, 167 
 Neutral tint re (lector, 205 
 Nitrate of silver staining, 266 
 Nitric acid, 313, 314 
 Nit/schia sigmoidca, 141 
 
 lanceolata, 141 
 
 Nobert's bands, 119 
 Noctiluca miliaris, 137 
 Nodosaria raphanus, 144 
 Nose-piece, double, 60 
 
 Swift's centering, Go 
 
 Numerical apertures, 125 
 
 O. 
 
 OBJECTIVES, 9, 45 
 
 amplifying power of, $3 
 
 Hartnack, 54 
 
 Zeiss, 55 
 
 construction of, 47 
 
 correction of, for photomicro- 
 graphy, 210 
 
 depth of focus of, 114 
 
 homogeneous-immersion, 12 1 
 
 immersion, 104, 121 
 
 improvements in, 46 
 
 low angle, 106 
 
 i -inch, 51 
 
 proposed classification of, 105 
 
 selection of, 49 
 
 separating, 48 
 
 Swift's short mounted, 52 
 
 Wenham's new formula for, 52 
 
 Object of dissecting, 177 
 Objects, collection of, 127 
 delineation of, 203 
 
 by ruled squares, 204 
 
 for polariscope, 248 
 
 Oculars, 40 
 
 American nomenclature, 43 
 
 cleaning, 44 
 
 relative power of, 43 
 Odontophore, 153 
 - of Patella vulgata, 153 
 Oi. I in in aurantiacum, 144 
 Oil-immersion condensers, 68 
 ofcajeput, 317 
 
 Oil of cloves, 317 
 
 of vitriol, 313 
 
 Old works on microscopy, 3 
 
 Opaque injections, 268 
 
 Orbitolites complanatus, 144 
 
 Ordinary ray, 238 
 
 Organisms, life-history of, 3 
 
 Orthoptera, 146 
 
 Orthoscopic eye-piece, Reiner's, 42 
 
 Osborne's illuminator, 74 
 
 Oscillatoria, 132 
 
 Osmic acid, hardening, 314 
 
 staining, 265 
 
 Over-corrected lenses, 106 
 Over-exposed negatives, 214 
 Oxydising agents, 314 
 Oyster, organs of, 179 
 
 P. 
 
 PAPER cells, 284 
 
 Papulaspora sepidonioides, 144 
 
 Parabolic reflector, 79 
 
 Paraboloid, 77 
 
 immersion, 78 
 
 Paramecium aurelia, 129, 134 
 
 Parasitica, 146 
 
 Parasite, spectrum of, 253 
 
 Parmelia parietina, 150 
 
 Patella vulgata, 153, 178 
 
 Pelargonium, petal of, no 
 
 Penetrating power, 103, 113 
 
 Penetration, Abbe's researches on, 1 14, 
 
 "5 
 
 Penicillium crustaceum, 144 
 setophilum, 144 
 Periwinkle, 178 
 
 organs of, 1 79 
 
 Peronospora infestans, 144 
 
 viciae, 144 
 Peronosporites, 201 
 Pertusaria communis, 151 
 Petal of pelargonium, 1 10 
 Petroleum naphtha, 317 
 Petrological microscope, 245 
 Petrology, 246 
 Philodina megalotrocha, 146 
 Phosphoric acid, 313 
 Photographing on wood, 227 
 Photographic varnish, 322 
 
332 
 
 INDEX. 
 
 Photographing Amphipleura 
 
 220 
 
 Photo-micrography, 208 
 
 camera for, 208, 209, 213 
 
 correction of objectives for, 210 
 
 drying negatives, 225 
 
 electric light, 217 
 
 fixing image, 225 
 
 magnesium light, 219 
 
 sun light, 214 
 
 Table of amplifications, 208 
 
 working with eye-pieces, 209 
 
 Physcia ciliaris, 151 
 
 Picro-carmine staining, 263 
 
 Pine wood, section of, 1 10 
 
 Pinnularia radiosa, 141 
 
 viridis, 141 
 
 Piths, stained, 259 
 
 Pitted vessels, 259 
 
 Plain mirrors, 98 
 
 Plano-convex lenses, 101 
 
 Platyscopic lens, 5 
 Pleurobrachia pileus, 160 
 Pleurosigma angulatum, 103, 118 
 Pocket lenses, 4 
 
 microscope, 139, 140 
 
 Podocyrtis Schomburgii, 155 
 Podura, no, 148 
 Podura-cage, 310 
 Polariscope, 238 
 Polarizing objects, list of, 248 
 
 prism, 238, 239 
 
 Polishing lap, 196 
 
 Pollen, Althea rosa, 107, 158, 296 
 
 hollyhock, 107 
 
 Polyactis fascicularis, 144 
 Polycistina, 151, 154 
 arranged slides of, 294 
 Polyommatus argus, in, 148 
 Polypide, 155 
 Polystomella crispa, 144 
 Polyzoa, 155 
 Pond filter, 130 
 
 scoop, 128 
 
 Porphyrine, 151 
 
 Positive eye-piece, Ramsden's, 42 
 
 Postage of slides, 311 
 
 Potash, 313, 319 
 
 Powell & Lealand's binocular prism, 33 
 
 Powell & Lealand's oil -immersion con- 
 denser, 68 
 
 stand, 13 
 
 vertical illuminator, 75 
 
 Power, amplifying, of objectives, 53^ 
 
 relative, of oculars, 43 
 
 Preparation and mounting of objects, 
 271 
 
 Preparing animal tissues, 190 
 
 Preserving insects for dissection, 173 
 
 zoophytes, 161 
 
 Prism, Amici's, 73 
 
 analysing, 239 
 
 Nachet, 74 
 
 Nicol's, 239 
 
 Stephenson's binocular, 35 
 
 Wenham's binocular, 32 
 
 Woodward's, 73 
 
 Pritchard's microscopic cabinet, 2 
 
 Proboscis of blow-fly, 108 
 
 Pteris aquilina, 142 
 
 Ptilota, 133 
 
 Puccinia graminis, 144 
 
 Purifying diatoms, 139 
 
 Pyrogallic acid and iron, 265 
 
 developer, 221 
 
 Q. 
 QUARTZ-PLATE, Klein's, 242 
 
 action of Nicol prism on, 
 
 243 
 
 rotatory polarisation on, 242 
 
 scale, 255 
 
 Quekett's treatise, 2 
 
 R. 
 
 RALF'S liquid, 320 
 Ramsden's eye-piece micrometer, 232 
 
 positive eye-piece, 41 
 
 screw micrometer, 234 
 
 Razor guards, 187 
 
 Reade's condenser, 67 
 
 Reagents, 312 
 
 Real images, 6 
 
 Recipes, 318 
 
 Redmayne's collecting apparatus, 138 
 
 Red ringing varnish, 323 
 
 Reflector, neutral tint, 205 
 
 parabolic, 79 
 
 side, 80 
 
INDEX. 
 
 333 
 
 Reflex illuminator, Wenham's, 71 
 Refraction of light, 97 
 Refractive indices, Table of, 98 
 Relative power of oculars, 43 
 Resolving power of objectives, 103, 117 
 Revolving table, 90 
 Rezner's mechanical finger, 294 
 Rhinoceros horn, 244 
 Rhomb of Iceland spar, 240 
 Rhopalocanium ornatum, 155 
 Rhopalomyces pallidus, 144 
 Ringing varnishes, 323 
 Rings in biaxial crystal, 246 
 Rock-sections, cutting, 199 
 
 mounting of, 297 
 
 Rosewood slips, 274 
 Ross, early objectives, 46 
 
 model, II 
 
 stands, 10, 12 
 
 Zentmayer's stand, 27 
 
 Rotatoria, 145 
 
 Rotifer trap, 83 
 
 Rutherford's microtome, 185, 194 
 
 SAFETY cage, 89 
 Salpina redunca, 134 
 Saws of saw-fly, 174 
 Scale of Podura, no 
 Sciopticon, 212, 228 
 Scissors, 169 
 
 Scolopendrium vulgare, 142 
 Sea-anemones, 160 
 Section-cutter, common, 184 
 
 Haile's, 184 
 
 Hoggan's, 201 
 
 Matthews', 202 
 
 Rutherford's, 185, 194 
 
 Swift's, 1 86 
 
 Section-knives, 187 
 
 lifter, 184 
 
 Sections, animal, 193 
 
 bleaching, 260 
 
 bone, cutting, 201 
 
 coal, cutting, 200 
 
 cutting, 182 
 
 bedding agents for, 188 
 
 Echinus spine, 112, 113, 200 
 
 frog's lung, 115 
 
 Sections, horse-chestnut, 108 
 
 human liver, 117 
 
 lichens, 190 
 
 mounting, 308 
 
 pine wood, 1 10 
 
 rocks, 199 
 
 teeth, 20 1 
 
 vegetable, 1 89 
 
 wood, 156 
 
 Selection of objectives, 49 
 Selenite films, 241 
 
 Barker's, 241 
 
 stage, 241 
 
 Sending slides by post, 310 
 Separating diatoms, 294 
 
 objectives, 48 
 
 Short-mounted objectives, 52 
 
 Side reflectors, 80 
 
 Siphonoptera, 146 
 
 Size, 267 
 
 Slags, 151 
 
 Slide box, Stokes's, 309 
 
 centerer, 274, 275 
 
 sending by post, 310 
 
 Slips, 97 
 Slitter, 195 
 
 charging with diamond dust, 196 
 
 Slitting and polishing bench, 195 
 
 Smith's mounting instrument, 308 
 
 Soda, 313 
 
 Softening agents, 312 
 
 Solar heat, 215 
 
 Solvents, 316 
 
 Sorby's wedge cell, 25 1 
 
 Spectra of various substances, 253 
 
 Spectroscope, 249, 256 
 
 Spectroscopic maps, 257 
 
 Spencer's early objectives, 46 
 
 Spicer's fluid, 319 
 
 Spine, Echinus, section of, 112, 113, 200 
 
 Sporocybe alternat,a, 144 
 
 Spot lens, 77 
 
 Spring clips, 300 
 
 scissors, 169 
 
 Stachybotrys lobulata, 144 
 
 atra, 144 
 
 Stage-forceps, 81 
 
 rotating, 82 
 
 Staining and injecting, 259 
 
334 
 
 INDEX. 
 
 Staining animal sections, 265 
 
 bioplasm, 267 
 
 carmine and green, 262 
 
 chloride of gold, 266 
 
 logwood, 259 
 
 nitrate of silver, 266 
 
 osmic acid, 265 
 
 picro-carmine, 263 
 
 pyrogallic acid and iron, 265 
 
 tannin and magenta, 266 
 
 Stand, Beck's, 14 
 
 Economic, 36 
 
 Browning's portable, 22, 23 
 
 rotating, 21 
 
 Bulloch, 25 
 
 Collins' Harley, 18 
 
 Crouch, 20 
 
 Powell and Lealand, 13 
 
 Ross, 10, 12 
 
 Zentmayer, 27 
 
 " - Stephenson's binocular, 34 
 
 Swift's Challenge, 1 6 
 
 Watson's patent, 30 
 
 Stanhope lens, 5 
 Starches, 158, 159 
 
 under polarised light, 243 
 
 Starch - granules, mounting of, 295, 
 
 304 
 
 Steinheil's lenses, 5 
 Stephanoceros Eichornii, 146 
 Stephenson's binocular microscope, 34 
 
 prism, 35 
 
 safety cage, 89 
 
 Sting of humble bee, 175 
 
 wasp, 176 
 
 Stokes's slide box, 309 
 
 Substage illuminator, 69 
 
 Sulphate of copper cell, 96 
 
 Sunlight method of photomicrography, 
 
 214 
 Swift's petrological microscope, 244 
 
 short mounted objectives, 52 
 
 Syringe, 170 
 
 T. 
 
 TABLE of Abbe's experiments of depth 
 
 of vision, 115 
 amplifying power of single lenses, 
 
 8 
 
 Table of apertures, 126 
 
 corrections of visual and actinic 
 
 foci, 212 
 
 exposures, photomicrography, 213 
 
 erector amplifications, 166 
 
 magnifying power of eye-pieces 
 
 and objectives, 53 
 
 Hartnack, 54 
 
 Zeiss, 55 
 
 micras and micromillimetres, 231 
 
 Mb'ller's test-plate, 120 
 
 natural sines, 236 
 
 Nobert's test-plate, 119 
 
 penetrating and illuminating 
 
 power, 116 
 
 photomicrographical amplifica- 
 tion, 208 
 
 proposed catalogue for objectives, 
 
 105 
 
 refractive indices, 98 
 
 relative power of oculars, 43 
 
 revolving, 91 
 
 Tannin, 314 
 
 Teeth, cutting sections of, 201 
 
 Telescopic walking-stick, 128 
 
 Thin glass covers, 97, 275 
 
 measuring wedge for, 275 
 
 Thwaites's fluid, 320 
 
 Tiletia caries, 144 
 
 Tissues, hardening animal, 191 
 
 preparing animal, 190 
 
 Tolles' binocular eye-piece, 33 
 
 interior illuminator, 76 
 
 Toning baths, 226 
 
 Tourmaline, 240 
 
 Tow net, 129 
 
 Trachea of water beetle, 109 
 
 Transparencies for lantern, 228 
 
 Transparent injections, 268 
 
 Treatise, Baker's, 2 
 
 Goring's, 2 
 
 Pritchard's, 2 
 
 Quekett's, 2 
 
 Triarthra longiseta, 134 
 
 Trichina spiralis, 193, 306 
 
 Triplexicon, 212, 228 
 
 Troughs, Better-ill's, 87 
 
 dissecting, 167 
 
 zoophyte, 85 
 
INDEX. 
 
 335 
 
 Tubularia ramea, 160 
 Tulley's achromatic, 45 
 Turacus albocristatus, 254 
 Turntables, 276-283 
 Turntable, Armstrong's, 279 
 
 Aylward's, 283 
 
 Bridgman's, 277 
 
 Butterworth's, 278 
 
 Congress, 280 
 
 Cox's, 278 
 
 Dunning's, 282 
 
 Kinne's, 279 
 
 Matthews', 276 
 
 Rolfe's, 281 
 
 Shadbolt's, 276 
 
 Zentmayer's, 277 
 
 Turpentine, 314 
 bleaching in, 299 
 
 U. 
 
 UNDER-CORRECTED lenses, 106 
 Uni axial crystals, rings in, 247 
 Useless paraphernalia, 4 
 Usnea barbata, 150 
 Ustilago segetum, 144 
 
 V. 
 
 VALENTINE'S knife, 183 
 
 Maddox's form of, 183 
 
 Vallisneria spiralis, 116 
 Varnish cells, 284 
 Varnishes, 321-323 
 
 Vegetable matter, disintegration of, 
 180 
 
 dissection of, 179 
 
 preparations, 157 
 
 section-cutting, 189 
 
 Vertical illuminators, 75 
 Virtual images, 6 
 Vivarium, 149 
 Volvox globator, 132 
 
 W. 
 
 WALKING-STICK, telescopic, 128 
 Wash bottle, 270 
 Wasp, sting of, 176 
 Watchmaker's lenses, 4 
 Water beetle, trachea of, 109 
 Watson's patent stand, 20 
 Wax cells, 284 
 Wedge cell, Sorby's, 251 
 Wenham's binocular prism, 32 
 
 high power, 33 
 
 diatom illuminator, 72, 1 19 
 
 objectives, new formula for, 52 
 
 reflex illuminators, 71 
 
 Wet and dry plates, 213 
 
 Whalebone clip, 299 
 
 Wheat starch, mounting in dammar, 
 
 301 
 
 Whisker, cat's, 294 
 White cloud illuminator, 96 
 White zinc varnish, 323 
 Wide apertures, value of, 123 
 Wollaston's doublets, 45 
 Woodward's prism, 73 
 Wood, photographing on, 227 
 
 sections, 158 (FRONTISPIECE) 
 
 Working distance, 103 
 microscope, 38 
 
 Y. 
 
 YELLOW ringing varnish, 323 
 
 Z. 
 
 ZENTMAYER'S mechanical finger, 293 
 Zeiss's objectives, 55 
 Zincs for electric light battery, 218 
 Zoophyte, 160 
 
 troughs, 85 
 
 Zoophytes, preserving, 161 
 
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 sliding body for coarse . adjustment, screw fine adjustment, draw-tube, 
 circular glass stage, diaphragms, plano-concave mirror, with eye-piece, 
 superior -in. and i-in. object-glasses, in mahogany case. Price 4 los. 
 
 Accessory Apparatus for the "Student's Microscope" at 
 greatly reduced prices. 
 
 SEND POE MICRO-CATALOGUE, POST-FREE. 
 
 Largest and best Stock of New and Second-hand Photographic Lenses, 
 
 Cameras, and Apparatus, by all best Makers. 
 ILLUSTRATED PHOTO-CATALOGUE, POST-FREE. 
 
 Gentlemen residing in the Country can have goods forwarded op, 
 approval on receipt of deposit for the amount. 
 
 PURCHASES AND EXCHANGES MADE. 
 
 HUNTER AND SANDS, 20 CRANBOURN STREET, LONDON, 
 
LIST OF PRICES 
 
 Of the Instruments referred to in this Work made by 
 
 JOHN BROWNING. 
 
 Bro Wiling 1 ' S Platyscopic Lenses, figure 2, pages 5 and 6, magnifying 10, 15, 20, or 30 
 diameters. Price each power, i8s, 6</. 
 
 Browning's Rotating- Stag-e Microscope, figure n, page 21, with i-in. and i-in. 
 Object-glasses. Price 10 10*. 
 
 Browning's New Portable Microscope, figures 12 and 13, pages 21, 22, and 23. 
 Price, complete in case, but without Objectives, 22. 
 
 Stephenson's Binocular Microscope, figures 19, 20, and 21, pages 34 and 35. Price 
 complete, with pair of Eye-pieces and two Objectives, i-in. and 4-inch, .20. 
 
 Microscope Lamp, figures 81 and 82, pages 91 and 92. 12*. bd. and 1 i6s. 
 
 Browning's Pocket Microscope, figure 124, page 140. Price ^i us. 6d. 
 
 Houston's Botanical Dissecting Microscope, figure 149, page 163. 6*. 6d. 
 
 Browning's Lantern Microscope, figure 200, page 229, complete with Objectives. 
 Price s ios. 
 
 The Sorby-Browning Microspectroscope, figure 216, page 250. Price 6. 
 
 The Sorby-Browning Microspectrostfope, with bright point Micrometer, figure 
 221, page 256. Price .8 5^. 
 
 List of Microscopes sent free. 
 
 Illustrated Catalogue of Microscopes, containing 33 Engravings, 8 'whole page, 
 sent for six stamps. 
 
 JOHN BROWNING, 
 
 Optician to Her Majesty's Government, the Royal Society, the Royal 
 Observatories of Greenwich, Edinburgh, &c., &c., 
 
 63, STRAND, LO 1ST DO 1ST, W. C. 
 
 LIVING SPECIMENS FOR THE MICROSCOPE. 
 
 THOMAS BOLTON, 
 
 57, NEWHALL STREET, BIRMINGHAM. 
 
 SPECIMEN TUBE ONE SHILLING, 
 
 A Series of Twenty-six Tubes in course of Six Months (or as required) 
 for a Subscription in advance of ^i is. 
 
 Portfolio of Drawings, Six Parts, Is. each. 
 
 HINTS ON THE PRESERVATION OF LIVING OBJECTS, 
 
 AND 
 
 THEIB EXAMINATION UNDER THE MICROSCOPE. 
 
 THREEPENCE. 
 
 Price List on receipt of Stamped and Directed Envelope- 
 
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