B10LOSY 
 
 LIBRARY 
 
 G 
 
LECTURES ON BACTERIA 
 
 DE BARY 
 
HENRY FROWDE 
 
 OXFORD UNIVERSITY PRESS WAREHOUSE 
 AMEN CORNER, E.C. 
 
LECTURES 
 
 ON 
 
 BACTERIA 
 
 BY 
 
 A. DE BARY 
 
 PROFESSOR IN THE UNIVERSITY OF STRASSBURG 
 
 SECOND IMPROVED EDITION 
 
 AUTHORISED TRANSLATION BY 
 
 HENRY E. F. GARNSEY, MA. 
 
 Fellow of Magdalen College, Oxford 
 
 REVISED BY 
 
 ISAAC BAYLEY BALFOUR, M.A., M.D., F.R.S. 
 
 Fellow of Magdalen College and She rardian Professor of Botany 
 in the University of Oxford 
 
 WITH 20 WOOD-ENGRAVINGS 
 
 AT THE CLARENDON PRESS 
 
 1887 
 
 [ All rights reserved ] 
 
BIOLOSY 
 
 LIBRARY 
 
 G 
 
PREFACE TO THE ENGLISH 
 EDITION. 
 
 THIS translation of Professor De Bary's ' Vorlesungen iiber 
 Bacterien' has been prepared because there is at present 
 no book in English which gives in like manner ' a general 
 view of the subject ' of Bacteria, and ' sets forth the known 
 facts in the life of Bacteria in their connection with those 
 with which we are acquainted in other branches of natural 
 history.' 
 
 I. B. B. 
 
 OXFORD, 1887. 
 
AUTHOR'S PREFACE. 
 
 THE present work is in the main a short abridgement of a 
 number of lectures, some of which were delivered in a connected 
 series as a University course, others as occasional and separate 
 addresses. The form of the lectures has been occasionally 
 altered to meet the difference between a written treatise and free 
 oral delivery accompanied by demonstrations. Some things 
 have been omitted and others added, especially some matters of 
 general importance which were not published or did not become 
 known to me till after the delivery of the actual course. 
 
 The lectures were an attempt to introduce an audience com- 
 posed of persons of very different professional pursuits, medical 
 and non-medical, to an acquaintance with the present state of 
 knowledge and opinion concerning the much discussed questions 
 connected with Bacteria. They had, therefore, to give such a 
 survey of the subject as would be intelligible to all who were 
 not strangers to the elements of a scientific training, and 
 especially to set forth the known facts in the life of the 
 Bacteria in their connection with those with which we are 
 acquainted in other branches of natural history. 
 
 A survey of the present extensive literature of the subject, 
 and of the almost daily additions to it, shows the existence of 
 many serviceable and some excellent publications, but at the 
 same time also of much that is mistaken and obscure. The 
 scientific and semi-scientific converse of the day, if I may use 
 
viii Preface. 
 
 the expression, is greatly influenced by works of the latter kind, 
 and the chief reason for this, if I am not mistaken, lies in the 
 absence of a general view of the subject itself and of its relations 
 to other portions of natural history; we cannot see the wood for 
 the trees. An attempt to give such a view would be no mere 
 superfluous addition to existing works, and this consideration 
 was a decisive reason in the judgment of myself and of those 
 who gave me their encouragement for afterwards transcribing 
 and publishing my lectures. 
 
 The present treatise, therefore, must not be expected to be 
 a Bacteriology, or even to report and enumerate all the details 
 which may be of interest and importance ; it should rather 
 serve only as a guide for the direction of the student through 
 these details. 
 
 Many readers, devoted to the study of the Bacteria, will be 
 familiar with the literature or with the guides to it before they 
 take up this book. For the sake of those who seek to gain 
 some knowledge of the subject from its perusal, and also for 
 the purpose of naming the most important sources of informa- 
 tion which I have made use of along with my own investigations. 
 I have added a few notices of publications at the end of the 
 volume, and have indicated by numerals in brackets the places 
 in the text to which the citation marked with the same number 
 refers. 
 
 So much by way of introduction to this little work. I trust 
 that it may do something to clear up existing views on the 
 subject of the Bacteria, and to lead the investigation of these 
 organisms from its present stage of storm and pressure into the 
 ways of quiet fruitful labour and increase of knowledge. 
 
 The above with the omission of one sentence is the word- 
 ing of the preface written in July, 1885, for the first edition of 
 this book. The kindly reception which it met with can only 
 
Preface. ix 
 
 have been due to the circumstance that the form in which the 
 subject was presented in it was the one best adapted to attain 
 the object proposed ; it could scarcely be that there was any- 
 thing new in it. Hence the form and limits of the second 
 edition which is now demanded are alike prescribed to me ; 
 it must be made as like as possible to the first. This has been 
 done ; the original frame is unaltered, and the old matter still 
 appears in it in many places. On the other hand, much pro- 
 gress has been made in the period which has elapsed since the 
 work was originally composed, and some new views have been 
 laid down which could not be disregarded. The new edition, 
 therefore, will be found to contain not only some editorial 
 improvements in the special descriptions, but also various 
 important alterations. 
 
 These observations apply also to the notes at the end of the 
 work, except that I have introduced somewhat more critical and 
 explanatory remarks than in the first edition. 
 
 A. DE BARY. 
 
 STRASSBURG, Oct., 1886. 
 
CONTENTS. 
 
 I. Introduction. Bacteria or Schizomycetes and Fungi. Struc- 
 ture of the Bacterium-cell . . . : . . . i 
 
 II. Cell-forms, cell-unions, and cell-groupings .... 9 
 
 III. Course of development. Endosporous and Arthrosporous 
 
 Bacteria . . . ...'*. . . 15 
 
 IV, Species of Bacteria. Distinct species denied. The grounds 
 for this denial insufficient. Method of investigation. 
 Relationships of the Bacteria and their position in the 
 system 24 
 
 V. Origin and distribution of Bacteria . . . . . 37 
 
 VI. Vegetative processes. External conditions : temperature and 
 material character of the environment. Practical ap- 
 plication of these in cultures, in disinfection, and in 
 antisepsis . . . . . ' Y Y . 49 
 
 VII. Relation to and effect upon the substratum. Saprophytes 
 and Parasites. Saprophytes as exciting decompositions 
 and fermentations. Characteristic qualities of Forms 
 exciting fermentation . . . . . . . 64 
 
 VIII. Most important examples of Saprophytes. The nomenclature 
 explained. Aquatic Saprophytes: Crenothrix, Cladothrix, 
 Beggiatoa; other aquatic forms . . -. . .- . 7 2 
 
 IX. Saprophytes which excite fermentation. Fermentations of 
 urea. Nitrification. Acetous fermentation. Viscous 
 fermentations. Formation of lactic acid. Kefir. Bacillus 
 Amylobacter. Decompositions of proteid. Bacterium 
 Termo 83 
 
 X. Parasitic Bacteria. The phenomena of parasitism . . 107 
 

 xii Contents. 
 
 PAGE 
 
 XI. Harmless parasites of warm-blooded animals. Parasites of 
 the intestinal canal. Sarcina. Leptothrix, Micrococci, 
 Spirillum, Comma-bacillus of the mucous membrane of 
 the mouth 115 
 
 XII. Anthrax and Fowl- cholera 122 
 
 XIII Causal connection of parasitic Bacteria with infectious 
 diseases, especially in warm-blooded animals. 
 Introduction . . . ' . 
 
 Relapsing fever 
 
 Tuberculosis 
 
 Gonorrhoea 
 
 Asiatic Cholera '.--.... . . ... \ 
 
 Traumatic infectious diseases . . 
 Erysipelas . . f . ; . . 
 
 Trachoma and xerosis ; pneumonia, leprosy, syphilis, 
 
 cattle-plague . . . . . ,, .. . 169 
 
 Malaria . . . . . . . .170 
 
 Typhoid fever and diphtheria . . . ' " ' ". ' - . 171 
 Infectious diseases in which the presence of contagium 
 
 vivum has not been demonstrated . . . . 1 74 
 
 XIV. Diseases caused by Bacteria in the lower animals and in 
 plants. 
 
 Diseases of insects . . . v ..." . _ ,' . 174 
 
 Diseases of plants . -. - , . ; : : . - . . 177 
 
 Conspectus of the Literature and Notes ..'.'.. . 181 
 Index of Names . . . ... . . . 191 
 
I. 
 
 Introduction. Bacteria or Schizomycetes and Fungi. 
 Structure of the Bacterium-cell (1). 
 
 THE purpose of these lectures is to give some account of the 
 present state of our knowledge respecting the objects included 
 under the name of Bacteria. It is unnecessary to enlarge upon 
 the manifold interest attaching to these organisms at a time when 
 the statement urged daily on the educated public does not fall far 
 short of saying, that a large part of all health and disease in the 
 world is dependent on Bacteria. If we are therefore spared that 
 customary portion of the introduction to a lecture which seeks 
 to impress the hearer with the importance of the subject, it be- 
 comes the more necessary to give prominence from the first to 
 the reverse side of the question ; that is to say, to call special 
 attention to the fact, that the problem presented to us can only 
 be solved by quiet scientific examination from every possible 
 point of view of the objects under consideration; and a study of 
 this kind is dry rather than exciting, or to use a common ex- 
 pression, interesting. But this should not deter any one who 
 is really desirous of acquiring some knowledge of our subject. 
 
 The order of our remarks will follow the natural arrangement 
 .of the subject before us; and our first task therefore will be to 
 ''enquire what Bacteria are ; in other words, to make ourselves 
 acquainted with their conformation, their structure, their de- 
 velopment, and their origin in connection with their development. 
 Next, we have to enquire what they do, what good and what 
 
2 Lectures on Bacteria. [ i. 
 
 harm they occasion, that is, we must study their vital processes 
 and the effects which these produce on the objects outside of 
 themselves. 
 
 We begin with the first question, and we will first of all bestow 
 a moment's consideration on the name. 
 
 Bacteria, meaning rod-shaped animalcules or plantlets, from 
 the rod-like form which many of them exhibit, are also termed 
 Fission-fungi or Schizomycetes. The two expressions are not, 
 strictly speaking, of the same import. 
 
 The reason of this is that the word Fungi is used in two 
 senses. In the one it is the name for those lower flowerless 
 plants which are devoid of chlorophyll, the green colouring 
 matter of leaves, and hence exhibit certain definite peculi- 
 arities in the process of their nutrition. We shall speak of 
 these peculiarities at greater length in succeeding lectures; 
 at present we will only make the preliminary observation, 
 that all organisms devoid of chlorophyll require already formed 
 organic carbon-compounds for their nutrition, and cannot obtain 
 the necessary supplies of carbon from the carbon dioxide which 
 finds access to them. The construction of organic compounds 
 from this substance is bound up with the presence of chlorophyll 
 and analogous bodies. 
 
 Fungi in this sense are therefore a group characterised by 
 definite physiological peculiarities the mark of which is the 
 absence of chlorophyll, somewhat in the same way as birds and 
 bats may be grouped together under the head of winged 
 creatures. 
 
 In the other sense, that of descriptive taxonomic natural 
 history, the term Fungi denotes a group of lower plant-forms 
 distinguished by definite characteristics of structure and develop- 
 ment, and recognised at once when we see a mushroom or a 
 mould. The members of this group are all as a matter of fact 
 devoid of chlorophyll, but they might contain chlorophyll and 
 yet belong to this group, just as a bird may have no apparatus 
 for flight and yet be allowed to be a bird. To these Fungi, as 
 
i.] Structure of the Bacterium-cell. 3 
 
 defined by natural history and not by physiological characters 
 only, Bacteria are as little related in structure and development 
 as bats are to birds ; the relationship is even less, because there 
 are a few, though only a few, true Bacteria which contain chlo- 
 rophyll and decompose carbon dioxide, and which are therefore 
 not Fungi in the physiological sense. 
 
 For these reasons we shall be more strictly correct if we 
 speak on the present occasion of Bacteria rather than of Fission- 
 fungi ; but so long as we are quite clear as to the difference in 
 the meaning of the two words, it is a matter of no importance 
 which we use. 
 
 The conformation, structure, and growth of Bacteria are 
 extremely simple, if we put out of sight certain phenomena of 
 propagation and consider only the vegetative state. 
 
 Bacteria appear in the form of round or cylindrical rod-shaped, 
 rarely fusiform, cells of very minute size. The diameter of the 
 round cells or the transverse section of the cylindrical cells is in 
 most cases about o'ooi mm. ( = i micromillimetre = i /z) or even 
 less. The length of the cylindrical cells is 2-4 times the trans- 
 verse section, rarely more. There are only a few forms with dis- 
 tinctly larger dimensions. Putting aside, for later consideration, 
 the forms from the group of Beggiatoa, Crenothrix and their 
 allies, which differ to some extent in this and other respects from 
 the rest of the Bacteria, the greatest breadth yet observed is 4 /a, 
 the measurement given by Van Tieghem for the rod-shaped 
 cells of Bacillus crassus. 
 
 We are obliged to apply the term cells to those minute bodies, 
 because they grow and divide like plant-cells, and also because 
 all that we know of their structure agrees with the corresponding 
 phenomena in plant-cells. It is true that their small size does 
 not permit of our going at present very deeply into the minutiae 
 of their structure. Cell-nuclei, for instance, have not yet been 
 observed in them ; but this is the case in many small cells of 
 other plants of a low order of growth, especially Fungi, and till 
 recent times it was the case with respect to all fungal cells. 
 
 B 2 
 
4 Lectures on Bacteria. [$ i. 
 
 Perseverance and constantly improving methods of research 
 advance our knowledge as time goes on. 
 
 The Bacterium-cell is mainly composed of a portion of 
 protoplasm, which in the smaller and in most also of the 
 larger forms appears as an entirely homogeneous translucent 
 substance, but in some of the larger forms it is also often finely 
 granular or shows a different kind of structure, which will be 
 further described presently. It consists, as Nencki (2) has shown 
 in a number of cases, chiefly of peculiar albuminoid compounds 
 (mycoprotein, anthrax-protein) which vary with the species, and 
 its behaviour, when the usual empirical reagents are applied to it, 
 agrees in general with that of the protoplasmic bodies of other 
 organisms the yellow and brownish-yellow coloration with 
 solutions of iodine, and the absorption of, that is to say, the 
 intense staining by, preparations of carmine and anilin dyes. 
 Yarious specific differences occur in individual cases in the 
 behaviour of the protoplasm to these colouring reagents, and 
 supply very useful marks of distinction in certain cases which 
 will be mentioned again on subsequent occasions. 
 
 We have already alluded to the fact that the protoplasm of 
 certain Bacteria described by Engelmann and van Tieghem, 
 for example, Bacillus virens, v. T., is coloured by chlorophyll, 
 being of a uniform pale leaf-green hue. In the very large 
 majority of cases it is colourless ; most Bacteria, not only when 
 isolated under the microscope but also when collected into 
 masses, have a pure or dirty-white colour, and in the latter case 
 show various shades of tint inclining to gray or yellow, &c., 
 which the practised observer may even apply to the determina- 
 tion of species. On the other hand, there are not a few Bacteria 
 which exhibit lively colours when they are associated in masses, 
 yellow, red, green, violet, blue, brown, &c., according to the 
 individual. Schroter has collected together a number of such 
 cases. How far these colours belong to the protoplasm itself 
 or to its envelope, the cell-membrane, which will be described 
 presently, or to both, cannot in most cases be certainly ascer- 
 
i.] Structure of the Bacterium-cell. 5 
 
 tained, because the individual cell is so small that it does not by 
 itself show any indications of colour. In some comparatively 
 large forms, those, for instance, grouped together by Zopf under 
 the name of Beggiatoa roseo-persicina, it can be seen that the 
 living protoplasmic body shares at least in the coloration, which 
 in this case is a bright red. Some of the colouring matters in 
 question have been submitted to closer examination and have 
 even received special names, as bacterio-purpurin, &c. In their 
 optical qualities they show various points of resemblance to 
 anilin dyes, as is indicated by the above name ; but we must 
 not infer from this that the chemical composition is analogous. 
 
 Among other phenomena of frequent recurrence in the 
 structure and contents of the protoplasm the starch-reaction 
 claims special attention. Bacillus Amylobacter and Spirillum 
 amyliferum, v. T., in certain stages of their development have 
 this peculiarity, that a portion of their protoplasm, distinguished 
 from the remainder by being somewhat more highly refringent, 
 when treated with watery solution of iodine assumes an indigo- 
 blue colour like starch-grains, or speaking more exactly like 
 the granulose which forms a large part of their substance. The 
 conditions under which this phenomenon makes its appearance 
 and again disappears will be discussed at greater length below. 
 E.Hansen'sMicrococcusPasteurianus also and usually Leptothrix 
 buccalis show the granulose-reaction. We may also mention in 
 this connection the occurrence of sulphur-granules in Beggiatoa, 
 referring the reader to Lecture VIII for further particulars. 
 
 The protoplasmic body of the Bacteria is surrounded by a 
 membrane or cell-wall. This membrane in one of the species 
 which have been examined, Sarcina ventriculi (see Lecture XI), 
 possesses, as far as is at present known, the qualities of typical 
 plant-cellulose-membrane; it is firm and thin, and assumes 
 the characteristic violet colour when treated with Schulze's 
 solution. But in the majority of cases there is no trace of the 
 characteristic coloration of cellulose. In single specimens 
 scattered about in a fluid the membrane appears under the 
 
6 Lee hires on Bacteria. [ i. 
 
 microscope as a delicate line drawn round the free surface, and 
 forming the boundary between contiguous cells. It may even be 
 seen distinct from the protoplasm in the larger forms by the aid 
 of reagents which strongly contract the protoplasm and colour it 
 at the same time without affecting the membrane, for instance 
 alcoholic solution of iodine (see Fig. i, p\ It is plainly 
 shown also in the formation of spores which will be described 
 in Lecture III. This membrane, which lies close upon 
 the protoplasm, is in certain forms at least, the species of 
 Beggiatoa and Spirochaete for example, highly extensible and 
 elastic, for it is seen to follow the curves often made by the 
 elongated organism, and the protoplasm can alone be the active 
 agent in producing these. But the membrane which thus directly 
 covers the protoplasm is certainly in all cases only the innermost 
 firmer layer of a gelatinous envelope surrounding the proto- 
 plasmic body. This may be seen directly in not a few forms 
 if observed attentively under the microscope, when the cells 
 or small aggregations of cells lie isolated in a fluid. Large 
 masses of Bacteria are always more or less gelatinous or slimy 
 when in a sufficiently moist condition. When the cells are 
 dividing, the outer layers of the membrane may sometimes be 
 seen to swell up in succession. Hence, speaking generally, we 
 may say that the cells of Bacteria have gelatinous membranes, 
 with a thin and comparatively firm inner layer. The consistence 
 of the mucilage and its capability of swelling in fluids differ 
 in different cases, changing gradually, but this point will be 
 considered again presently at greater length. 
 
 The possession of gelatinous membranes of this kind is com- 
 mon to the Bacteria and to various other organisms of the lower 
 sort, of which Nostocaceae and some Sprouting and Filamentous 
 Fungi may be quoted as examples. In Bacteria, as in the latter 
 plants, the gelatinous membrane has been shown in a number 
 of forms which have been examined to consist of a carbohydrate 
 closely related to cellulose ; this is specially the case in the Bac- 
 terium of mother of vinegar and in Leuconostoc, the frog-spawn- 
 
i.] Stricture of the Bacterium-cell. 7 
 
 bacterium of sugar factories. On the other hand, Nencki found 
 that the membranes of certain putrefactive Bacteria not distinctly 
 determined are in a great measure composed, like the proto- 
 plasm which they enclose, of the mycoprotein mentioned on 
 page 4. Lastly, a statement of Neisser (65) must also be men- 
 tioned in this place ; he suspects, from the behaviour of the 
 membrane or envelope of the Bacterium of xerosis conjunctiva 
 in the presence of reagents, that it contains a considerable amount 
 of fatty matter. Further investigation into these points is at all 
 events desirable. The membranes of Cladothrix and Crenothrix 
 which live in water are often coloured brown by the introduc- 
 tion of compounds of iron. 
 
 Many Bacteria are capable of free movement in fluids. They 
 rotate about their longitudinal axis, or they oscillate like a 
 pendulum and move rapidly forwards or backwards. Search 
 has consequently been made for organs of motion, and these 
 are supposed to have been found in certain very slender filiform 
 appendages, cilia or flagella, which are attached singly or in 
 pairs to the extremities of rod-shaped Bacteria. Such cilia are 
 present in many relatively large cells not belonging to the Bacteria, 
 and endowed like them with the power of free movement in fluids, 
 the swarm-cells, for example, and swarm-spores of many Algae 
 and some Fungi. In these cases the cilia oscillate rapidly as 
 long as the movement continues, causing rotation round the 
 longitudinal axis, and may consequently be considered to be 
 the active organs of motion. In the swarm-cells of the Algae 
 they are processes, projections as it were, from the surface of 
 the protoplasmic body, and belong therefore to the protoplasm. 
 When the protoplasm is surrounded by a membrane, the cilia 
 pass out through openings in the membrane. But no such 
 characteristic structural conditions have been observed in the 
 Bacteria. Delicate thread-like processes have certainly been 
 observed occasionally at the points above-mentioned in coloured 
 specimens which have been exposed to desiccation. That they 
 are really there and not, or at least not always, in the imagina- 
 
8 Lectures on Bacteria. [ i. 
 
 tion of the observer only, is proved by the fact that they 
 appear in photographs. But in an overwhelming majority of 
 cases no cilia can be seen, though the Bacteria are capable of 
 independent movement and are examined with the best optical 
 aids after being killed and coloured. Where they are found, 
 they are as van Tieghem rightly says, not processes of the 
 protoplasmic body, but belong to the membrane, as is shown 
 by their behaviour with reagents, and must therefore be con- 
 sidered to be thread-like extensions of the soft gelatinous 
 membrane-layers. They have accordingly nothing in common 
 with the cilia of swarm-spores of the Algae, and cannot therefore 
 be regarded as organs of motion, since it was only from the 
 analogy of the cilia in the Algae that this function was inferred. 
 Such is the state of the case at least in the great majority of 
 species. Whether there are any exceptional cases must be deter- 
 mined by further investigation. It should be added, that among 
 lower organisms there are some comparatively large forms, 
 the Oscillatorieae, for example, the near relatives according to 
 our present knowledge of the Bacteria a point to be further 
 considered below which show similar movements, though no 
 cilia or other distinct organs of motion have been observed in 
 them. It follows that analogy does not require the discovery 
 of cilia in the Bacteria. 
 
 Vegetating Bacterium-cells multiply by successive division, 
 each cell forming two daughter-cells. When a cell has reached 
 a certain size, a fine transverse line makes its appearance in it, 
 dividing the cell into two equal parts. This line is subse- 
 quently shown by its gelatinous swelling to be the commence- 
 ment of a cell-membrane. This agrees with the phenomena 
 observed in the divisions of larger plant-cells, and there is 
 nothing to prevent our assuming that the details of the process 
 of division, which the minuteness of the object makes it impos- 
 sible to observe directly, are the same in both cases. 
 
 It must be acknowledged that the transverse wall which 
 appears as the cell divides is often so delicate as easily 
 
ii.] Cell-forms. 9 
 
 to escape observation, and becomes visible only under the influ- 
 ence of reagents which give a deep colour to the protoplasm 
 and make it shrink, especially alcoholic solution of iodine. 
 This must not be forgotten in determining the length of cells. 
 
 The successive bipartitions are either all in the same direction, 
 and the transverse walls are therefore parallel ; or more rarely 
 the walls lie in two or three directions in space, so that they 
 successively cut one another, and may actually cross at a right 
 angle. 
 
 II. 
 
 Cell-forms, cell-unions, and cell-groupings. 
 
 SINGLE Bacterium-cells, the simple structure of which has been 
 considered in the preceding chapter, may appear in very various 
 forms, the variety depending partly on their own shape and on 
 that of their simplest aggregations, partly on whether they are 
 united into larger aggregations or not, and on the peculiar 
 characters of these aggregations. 
 
 i. The shape of the individual cells and their simplest 
 genetic combinations give rise to the distinction into round- 
 celled, and straight or spirally twisted rod-like forms. A billiard- 
 ball, a lead pencil, and a cork-screw, so exactly illustrate these 
 three chief forms, that no one requires for his instruction in 
 this case the costly models which are offered for sale. The 
 figures on subsequent pages, which will be examined more 
 closely in later lectures, will for the present give a sufficiently 
 clear idea of the matter. 
 
 These forms have received a variety of names in the course 
 of the development of our knowledge. The round forms are 
 at present most commonly known as Cocci (Figs. 3, 4), and are 
 spoken of as Micrococci or Macrococci according to their size, 
 or as Diplococci when they still remain united in pairs after a 
 bipartition ; earlier writers called them monads, a name which 
 they applied to a variety of heterogeneous objects. 
 
io Lectures on Bacteria. -[$ IT. 
 
 The straight rod-forms (Figs, i, 2) have received the special 
 name of rods, Bacteria, from the earlier writers. Short or long 
 rods and other terms are obvious designations for subordinate 
 peculiarities of shape, but have no other value. 
 
 The screw or cork-screw forms are termed Spirilla, Spiro- 
 chaetae. Those which are only slightly curved, that is, which 
 form a portion only of a turn of the screw, being intermediate 
 between the two preceding categories, have been called by Cohn 
 Vibriones in accordance with the nomenclature of older authors. 
 It is well that we should understand clearly that these and other 
 names, which will be mentioned presently, are only used to define 
 the shapes of the organisms. It would indeed be better to give 
 them proper names expressive of their outward appearance, 
 and to use terms like sphere, screw ; and it is to be hoped 
 too that the jargon which prevails at present, especially 
 in medical literature, will gradually be replaced by a rational 
 terminology. 
 
 The cocci and rod-forms are sometimes liable to a peculiar 
 deviation from their ordinary shape ; single cells, lying between 
 other cells which remain true to one of the typical forms 
 described above, swell into broadly fusiform or spherical or oval 
 vesicles several times larger than the typical cells. This has been 
 observed in species of Bacillus, Cladothrix, &c., and with special 
 frequency in the Micrococcus of mother of vinegar. There is 
 some ground for assuming, though further proof is required, 
 that these swollen forms are the products of diseased develop- 
 ment, indications of retrogression and involution, and they were 
 therefore termed by Nageli and Buchner involution-forms (see 
 Fig. io). 
 
 2. According to the nature of the union or want of union of 
 the cells, we must first of all distinguish between the forms in 
 which genetic union and arrangement is maintained after succes- 
 sive bipartitions, and those in which it is severed or displaced. 
 
 When the cells continue united together in the connected 
 sequence of the divisions we have 
 
IL] Cell-unions, Cell-groupings. 1 1 
 
 a. The cells arranged in rows in the direction of the succes- 
 sive divisions. From their thread-like form these cell-rows 
 (Fig. 2, &c.) are termed filaments in accordance with the 
 traditional terminology; a strange confusion of ideas led to 
 their being also called pseudo-filaments, objects which look like, 
 but are not real, filaments. 
 
 It is obvious after the foregoing remarks, first, that these 
 filaments must be of different shape according as the individual 
 cells are round or of some other form ; secondly, that the 
 length of the filaments, measured by the number of cells, may 
 be very various. It may be said specially of the rod-like and 
 spiral forms, that the cells usually remain united into short 
 rows in such a manner that the rod or spiral is actually 
 composed of more than one cell, and then after a definite 
 increase of the entire length and of the number of the segment- 
 cells is divided into two at the oldest points of division. The 
 words Leptothrix, Mycothrix, and others designate the longer 
 filamentous forms. 
 
 b. Cells united together and arranged genetically in a simple 
 surface, or as a body of three dimensions, are of less frequent 
 occurrence, as has been already said ; Zopf s Bacterium meris- 
 mopoedioides may be given as an example of the former kind, 
 of the latter the cube-shaped cell-packets of Sarcina ventriculi 
 (see Fig. 14). 
 
 By the side of these phenomena of genetic union and variously 
 combined with them appears a series of groupings, as they may 
 be briefly termed, which owe their character to a great extent to 
 the mass, cohesion, and other specific qualities of the gelatinous 
 membranes as these are formed, and next and in combination 
 with these, to their own very various specific peculiarities, which 
 cannot, as a rule, be shortly defined ; some explanation of the 
 latter, though unfortunately only an imperfect one, will be given 
 further on when we are considering vital processes. The nature 
 also, and especially the state of aggregation of the substratum, 
 may in certain circumstances have an influence on the grouping. 
 
12 Lectures on Bacteria. [ n. 
 
 Thinness of the gelatinous membranes and a high degree of 
 capacity for swelling reaching to deliquescence will cause the 
 separation of cells or of the simplest cell-unions from one 
 another when growing in a fluid. Thick cell-membranes, and 
 a narrowly limited capacity for swelling in the gelatinous sub- 
 stance, will keep the cells united together in compact gelatinous 
 masses in the same fluid. These, which are the extreme con- 
 ditions, are actually found in nature, and all kinds of intermediate 
 states also occur. The firmer gelatinous masses (see Fig. 3) 
 are called by the old name Palmella, or by the more recent 
 name now commonly used, Zoogloea. The less sharply denned 
 Zoogloeae, as they may be shortly described, may naturally be 
 termed swarms. It depends on their specific gravity whether a 
 Zoogloea or a swarm will float on the surface or sink to the 
 bottom of the same fluid, while their general outline and the 
 grouping of the separate aggregates which compose them will 
 be fashioned in accordance with their further specific qualities. 
 
 To illustrate this point in passing by a few examples, 
 let us take three flasks containing a similar 8-10 per cent, 
 solution of grape-sugar and extract of meat in water. In one 
 flask the fluid is pretty uniformly clouded with the short motile 
 rods of Bacillus Amylobacter. In the second the surface of 
 the slightly clouded fluid is covered with a thick wrinkled scum, 
 dry on the upper surface, which is formed by Bacillus subtilis, 
 the so-called hay-bacillus. In the third the filaments of Bacillus 
 Anthracis, the Bacillus of anthrax which in other respects re- 
 sembles B. subtilis, form a flocculent deposit at the bottom of 
 the clear fluid. We can scarcely call this deposit by the name 
 of Zoogloea, we may perhaps call it a swarm. The hay- 
 bacillus-scum is properly a Zoogloea with a special characteristic 
 form. Formations more or less like it are found often enough 
 in fluids containing decomposable organic bodies. Highly 
 characteristic Zoogloeae developed in a fluid are the frog-spawn- 
 Bacterium of sugar-factories and the Bacterium of kefir. The 
 former is a round-celled organism, Leuconostoc, with a thick 
 
ii.] Cell-groupings. 1 3 
 
 compact gelatinous envelope which may fill entire vats with a 
 substance looking like frogs' spawn, and which will be con- 
 sidered again in a later lecture ; the term kefir-grains is applied 
 to the bodies employed by the inhabitants of the Caucasus in 
 the preparation from milk of a sourish beverage rich in car- 
 bonic acid. The kefir-grains are in the fresh living state white 
 bodies, usually of irregularly roundish form, equal to or ex- 
 ceeding a walnut in size. They have their surface crisped with 
 blunt projections and furrowed like a cauliflower ; they are of a 
 firm toughly gelatinous consistence, becoming cartilaginous, 
 brittle, and of a yellow colour when dried, and are chiefly com- 
 posed of a rod-shaped Bacterium. The small rods are for the 
 most part united together into filaments, which are closely 
 interwoven in countless zig-zags and firmly connected together 
 by their tough gelatinous membranes. It must also be observed, 
 that the Bacterium-filaments are not the only constituents of the 
 granules ; numerous groups of a Sprouting Fungus like the 
 yeast-fungus of beer are enclosed between them, especially in 
 the periphery, living and growing in common with the Bacterium, 
 but in much smaller quantity, and taking only a passive part in 
 the formation of Zoogloeae. 
 
 If Bacteria grow not in fluids but on some solid substance 
 which is only wet or moist, the grouping into Zoogloeae is a 
 frequent phenomenon even in those forms which separate 
 from one another in larger amounts of fluid owing to the 
 deliquescence of their gelatinous envelopes. The more limited 
 supply of water on the merely damp substratum is not 
 sufficient to make this gelatinous substance swell up to the 
 point of deliquescence. On decaying potatoes, turnips, and 
 similar substances we may often see small lumps of gelatinous 
 matter of a white or yellowish tint or of some other shade of 
 colour, and composed of these aggregations of Bacteria. These 
 lumps deliquesce in water. We have a special instance of the 
 kind in the often-described occurrence of the blood-portent, 
 Micrococcus prodigiosus (Monas prodigiosa of Ehrenberg), pro- 
 
14 Lectures on Bacteria. [ n. 
 
 ducing on substances rich in starch, such as dressed potatoes, 
 bread, rice, or wafers, moist blood-red spots which sometimes 
 spread rapidly and widely. Their colour has given rise to a 
 variety of superstitious notions when they have appeared 
 unexpectedly on objects of household use. They consist of 
 one of the chromogenous Bacteria which have been already 
 mentioned. 
 
 It was stated above that the grouping of different forms is 
 different in the same fluid, and in like manner the conformation 
 of the Zoogloeae on solid substances shows manifold variation 
 of forms which differ in other respects also. 
 
 These various facts connected with the grouping are them- 
 selves calculated to afford very valuable marks for character- 
 ising and distinguishing forms, the more valuable indeed in 
 proportion to the difficulty oftentimes of discriminating in- 
 dividual cells of such minute size under the microscope. It is 
 precisely in the phenomena of grouping that specific peculiarities 
 of conformation best display themselves, being collected together, 
 as it were, in larger quantity; these characters must indeed 
 be present in the single cell, but, with the means at present 
 at our disposal, it is difficult or even impossible to recognise 
 them there. But there is nothing peculiar in this. There 
 are many cells of gigantic size in comparison with the Bacteria 
 and highly differentiated, of which we cannot say with cer- 
 tainty when we see them by themselves whether they belong 
 to a lily or a tulip. But in their natural connection or grouping 
 some of them form a lily, others a tulip, and by this we know 
 that they are different. 
 
in.] Endosporous Bacteria. 1 5 
 
 III. 
 
 Course of development. Endosporous and Arthro- 
 sporous Bacteria. 
 
 THE different conformations and groupings described in the 
 preceding lectures indicate primarily nothing more than de- 
 finite forms of one phenomenon marked in each case by a 
 distinct name, such as present themselves at any moment of 
 observation, and without reference to their origin or future 
 destination. They are forms of the vegetative development, 
 growth-forms as they may be shortly termed, and correspond 
 to those which in the higher plants are designated by the words 
 tree, shrub, bulbous plant, and the like. Forms which are 
 determined only by their conformation correspond indeed only 
 to separate members of a particular growth, such as woody 
 stem, tendril, tuber, bulb, &c. 
 
 If we wish to know the significance of a tendril or a bulb in 
 the chain of phenomena, or indeed that of any other form of 
 living creature, we must answer the above questions of its 
 origin and destination, or, to use the customary form of words, 
 we must learn the course of its development. For every form 
 of living being taken at any one moment of time, though it 
 may be present in millions of specimens, is only a member of a 
 chain of periodic movements which coincide with a regular 
 alternation of forms. If therefore we wish for a more intimate 
 acquaintance with Bacteria, we must proceed to enquire into 
 their course of development. 
 
 As far as our present knowledge goes, this development is 
 not quite the same in all cases. We must distinguish two 
 groups, one of which contains the Endosporous, the other the 
 Arthrosporous Bacteria. 
 
 The former group consists of a number of straight rod- 
 forms which will here receive the special name of Bacillus, and 
 a few screw-twisted Spirilla. The phenomena, so far as they 
 
16 
 
 Lectures on Bacteria. 
 
 [$ 
 
 are known, are essentially the same in both, and they have now 
 to be described in detail in the case of Bacillus. See Fig. i. 
 
 The Bacilli in the highest state of vegetative development are 
 rod-shaped or shortly cylindrical cells with the characters already 
 described, which either remain isolated or are united together into 
 unicellular rods or longer filaments ; they are motile or motion- 
 less, and display active growth and division (Fig. i, ac], 
 Both growth and division at length come to an end, and then 
 begins the formation of peculiar organs of reproduction spores. 
 This process begins at the point to which it has been followed 
 furthest back with the appearance of a comparatively very minute 
 point-like granule in the protoplasm of a hitherto vegetative 
 cell. This granule increases in volume and soon presents the 
 
 appearance of an elon- 
 gated or round, highly 
 refringent, sharply-defined 
 body, which attains its 
 ultimate size rapidly, some- 
 times in a few hours, and 
 is then the mature spore 
 (Fig. i, d-f}. The spore 
 always remains smaller 
 than its mother-cell, the 
 protoplasm and other con- 
 tents of which disappear 
 with the growth of the 
 spore, being doubtless 
 consumed for its benefit, until at length the spore is seen sus- 
 pended in a pellucid substance inside the delicate membrane 
 of the mother-cell (Fig. i, r, h^. 
 
 Fig. i. Bacillus Megaterium. a outline sketch of a chain of rods in 
 active vegetation and motion, b pair of rods in active vegetation and 
 motion, p a 4-celled rod in this stage after treatment with alcoholic solution 
 of iodine, c 5-celled rod in the first stage of preparation for forming spores. 
 d-f successive states of a spore-forming pair of rods, d about 2 o'clock 
 
fin.] Endosporous Bacteria. 17 
 
 The details of these processes disclose sundry variations of 
 diagnostic value, especially in connection with the shape. In 
 Bacillus Megaterium, B. Anthracis, B. subtilis, for example, the 
 sporogenous cell does not differ in shape from the vegetative 
 cell, but in the two latter the mature spore is much shorter ; in 
 B. Anthracis it is slightly narrower, in B. subtilis often rather 
 broader than the mother-cell, in B. Megaterium it is a little 
 shorter but much narrower than the comparatively short 
 mother-cell (cf. Figs, i and 2). 
 
 In other species the spores are much smaller in every 
 direction than the mother- cell, and the latter is distinguished 
 from the cylindrical vegetative cell before or during the form- 
 ation of the spore by swelling into a permanent fusiform or 
 ovoid shape, either over the entire area of the cell or at the spot 
 where the spore lies, and which is then usually at one ex- 
 tremity of the cell. In the latter case, and also when cells that 
 are still cylindrical are attached on one side to a mother-cell 
 which has swollen up all over, the forms are produced which 
 were once known as capitate Bacteria, cylindrical Bacteria 
 with a capitate sporogenous swelling at the extremity. Ex- 
 amples of this kind are Bacillus Amylobacter (Fig. 13), B. 
 Ulna, and some others. 
 
 In Bacillus Amylobacter and Spirillum amyliferum, v. Tiegh., 
 the appearance of the spore is preceded by the formation of 
 granulose described above, and the spot where the spore 
 
 p.m., e about one hour later, /one hour later than e. The spores in /were 
 mature by evening ; no others were formed ; the one apparently commenced 
 in the third upper cell of d and e disappeared ; the cells in / which did 
 not contain spores were dead by 9 p.m. r a four-celled rod with ripe 
 spores, g- 1 five-celled rod with three ri;e spores placed in a nutrient 
 solution after drying for several days, at 12.30 p.m.; g z the same speci- 
 men about 1.30 p.m. ; g* about 4 p.m. h^ two dried spores with the mem- 
 brane of the mother-cell placed in a nutrient solution, about 11.45 a.m.; 
 h z the same specimen about 12.30 p.m. i, k, I later stages of germination 
 explained in the text on p. 2 1 . m rod dividing transversely, grown from a 
 spore placed eight hours before in a nutrient solution, a magnified 250 
 times ; the other figures 600 times. 
 
 C 
 
1 8 Lectures on Bacteria. [$ in. 
 
 begins to be formed is marked by the absence of granulose. 
 This spot looks in solution of iodine like a notch of a pale 
 yellowish colour, occupying one extremity of the rod which 
 elsewhere tends to be blue, and is moreover distinguished by 
 its lower power of refraction even before the use of a reagent. 
 As the spore grows in size the granulose disappears. Accord- 
 ing to Prazmowski the granulose is not always present before 
 the formation of the spore, even in Bacillus Amylobacter. In 
 other Bacilli, the three, for example, just previously named, it 
 has never been observed ; their protoplasm either remains un- 
 changed before spore-formation, or at most becomes a little 
 less transparent and in larger forms more evidently finely 
 granular. 
 
 A mother-cell, so far as can be positively stated, never pro- 
 duces more than a single spore. This can be determined with 
 certainty in almost all cases, and the few accounts which have 
 been given of the formation of two spores in a single cell are 
 doubtful, being unaccompanied by any guarantee that the 
 boundaries of adjoining cells have not been overlooked or 
 errors of other kinds admitted. I must, however, add that an 
 exception to the prevailing rule has recently come under my 
 own observation in the case of a species nearly allied to Bacillus 
 Amylobacter (see Lecture IX), which usually follows the rule, 
 but does also sometimes contain two spores in a cell which has 
 swollen and become broadly fusiform. I have not yet succeeded 
 in observing the further development of the twin spores. 
 
 In cultures formation of spores usually takes place when 
 other growth comes to an end because the substratum is no 
 longer adapted to maintain it, being either exhausted, as we 
 are in the habit of saying, or impregnated with the products 
 of decomposition which are unfavourable to vegetative develop- 
 ment. Formation of spores then spreads rapidly through the 
 larger number of the cells and through the special aggregations, 
 if the particular form is present in abundance. Some of these 
 it is true do not produce spores, in some the process begins 
 
$ in.] Endosporous Bacteria. 19 
 
 but is not completed. All cells which do not take part in 
 the normal formation of spores ultimately die and are de- 
 composed, if they are not transferred in good time to a fresh 
 substratum. 
 
 In other Bacilli, as B. Amylobacter, the procedure is dif- 
 ferent. Here spore-formation begins in single cells and spreads 
 by degrees to more and more of them, while a number of other 
 cells continue to vegetate and divide. We cannot therefore 
 regard the unsuitableness of the substratum to the vegetative 
 process as the cause which generally determines the formation 
 of spores. 
 
 By spores are usually meant such cells as are delimited 
 from a plant to develope again under favourable conditions 
 into a new vegetating plant. The commencement of this 
 latter process is termed germination. The bodies to which we 
 have here given the name of spores are so called because their 
 behaviour corresponds to that of germinating spores. As soon 
 as they are fully grown, that is, as soon as they are ripe, the 
 membrane of the mother-cell dissolves gradually or swells, and 
 the spores are thus set at liberty, retaining the characters 
 which have been already described; that is, they are round, 
 ovoid, or rod-shaped, according to the species, rarely of some 
 other shape, with a dark outline and usually colourless, but 
 with a peculiar bluish glistening appearance ; according to Cohn 
 the spore of Bacillus erythrosporus is tinged with red. Round 
 the dark outline may often be perceived a very pale and 
 evidently soft gelatinous envelope, which either covers the 
 spore uniformly all round, or is thicker at the two extremities 
 and drawn out into processes. 
 
 Germination shows that the spore is a cell surrounded by a 
 thin but very firm membrane, defined by the dark outline inside 
 the gelatinous envelope. Germination begins when the ripe 
 spore is subjected to the conditions favourable to the vege- 
 tation of the species, supply of water, suitable nutriment, and 
 favourable temperature. As it begins the spore loses its high 
 
 c 2 
 
20 
 
 Lectures on Bacteria. 
 
 [f "I. 
 
 
 
 Vi 
 
 l? 
 
 refringent power, its lustre and dark outline ; it assumes the ap- 
 pearance of a vegetative cell, and grows at the same time to the 
 size and shape of the vegetative cell from 
 which it sprang. With the completion 
 of this process movement begins in the 
 motile species, and this is followed by 
 the growth, division, and grouping which 
 have been described above as occur- 
 ring in the vegetative stages, and which 
 at length come to an end with a fresh 
 formation of spores. In many cases 
 a few hours only intervene between the 
 first observable commencement of ger- 
 mination and active vegetative growth. 
 See above, Fig. i, h-m. 
 
 With the first increase in size a mem- 
 brane is often seen to split and rise from 
 off the surface of the growing cell, being 
 evidently lifted from off it by a swelling 
 gelatinous outer layer surrounding the new 
 membrane of the cell. The rent through 
 the membrane is in the direction of 
 the length, or across the middle, accord- 
 ing to the species. The former is the 
 case according to Prazmowski in Bacillus Amylobacter, and it 
 occurs also in other species. The latter has been observed in 
 
 Fig. 2. A Bacillus Anthracis. Two filaments partly in an advanced 
 stage of spore- formation ; above them two ripe spores escaped from the 
 cells. From a culture on a microscope-slide in a solution of meat-extract. 
 The spores are drawn a little too narrow ; they are nearly as broad as the 
 breadth of the mother-cell. B Bacillus subtilis. I fragments of filaments 
 with ripe spores. 2 commencement of germination of spore ; the outer wall 
 torn transversely. 3 young rod projecting from the spore in the usual 
 transverse position. 4 germ-rods bent into the shape of a horse-shoe, one 
 afterwards with one extremity released. 5 germ-rods already grown to a 
 considerable size but with both extremities still fixed in the spore-membrane. 
 All magnified 600 times. 
 
 Fig. 2. 
 
$in.] Endosporous Bacteria. 21 
 
 B. Megaterium (Fig. i) and B. subtilis (Fig. 2, B)] the trans- 
 verse rent either extends quite across, so that half the membrane 
 is placed like a cap on each extremity of the cell, or the halves 
 remain attached on one side, so that the growing cell must 
 emerge from a gaping cleft (Fig. i , h-f). The ruptured mem- 
 brane is usually delicate and pale. In B. subtilis only it retains 
 at first the lustre and dark outline of the spore before ger- 
 mination, and hence it is probable that these phenomena have 
 their origin in the membrane. Sooner or later the membrane 
 thus torn from the cell swells and disappears. It may be owing 
 to the very early period at which the swelling sets in that 
 sometimes, as, for example, in B. Megaterium and B. Amylo- 
 bacter, the removal of the membrane is not perceptible in one 
 germinating spore, while it is clearly seen in others, and that in 
 other species, as in B. Anthracis, no removal of the membrane 
 takes place at all. 
 
 The longitudinal growth of the first cell in germination has 
 always the same direction in space as the longitudinal axis of the 
 spore or spore-mother-cell. This is the case also in Bacillus 
 subtilis, which appears at first sight to behave differently in this 
 respect. In this species the first rod-shaped germ-cell usually 
 emerges from the open transverse rent in the spore-membrane 
 in such a manner that its longitudinal axis crosses that of the 
 spore at a right angle, but this is not caused by a corresponding 
 divergence of the longitudinal growth, but by the circumstance 
 that when the germ-cell has attained a certain length it bends 
 through about 90, and thus projects on one side at a right 
 angle from the rent in the membrane. The bending of the 
 germ-cell is evidently caused by the resistance offered to the 
 elongation of the cell by the spore-membrane, which in this 
 species is highly elastic and is always ruptured on one side. 
 When growth is very rapid the two extremities of the young 
 rod may remain fixed in the membrane, and in that case the 
 middle portion projects in a curve from the aperture. It is not 
 till a later period, when the rods have begun to divide and 
 
22 Lectures on Bacteria. [ in. 
 
 separate into daughter-rods, that the latter straighten themselves 
 out. 
 
 Endogenous spore-formation, as it has now been described, 
 that is, formation of spores taking place inside the previously 
 vegetative cell, sharply distinguishes the endosporous forms from 
 the rest of the Bacteria, which we have termed arthrosporous. 
 The name is intended to indicate the fact, that in these forms 
 members of an aggregation or of a series of united generations 
 of vegetative cells separating from the rest assume the character 
 of spores immediately without previous endogenous rejuvenes- 
 cence, that is, they may become the origins of new vegetative 
 generations. In a number of the forms comprised in this divi- 
 sion, a more or less distinct morphological difference may be 
 observed between vegetative cells and spores; in others, as 
 far as we know at present, no such distinction is to be found. 
 
 Simple examples of the former kind are supplied by Leuco- 
 nostoc mentioned above and by Bacterium Zopfii, Kurth. The 
 former (Fig. 3) consists, according to van Tieghem's descrip- 
 tion, of curved bead-like rows of small round cells with firm 
 gelatinous coats united together in large numbers into Zoogloeae 
 (Fig. 3, a, b}. A large portion of the cells dies at the end of the 
 vegetative period when the nutrient substratum is exhausted. On 
 the other hand single cells irregularly distributed in the rows 
 become somewhat larger than the rest, acquire a more distinct 
 outline, that is, become thicker-walled, and their protoplasm 
 grows darker (Fig. 3, c). They at length become free by the 
 deliquescence of the gelatinous envelopes, and may claim the 
 name of spores, because when placed in a fresh nutrient solution 
 they develope into new rows of beads like those of the mother- 
 plant (Fig. 3, d-h). 
 
 Bacterium Zopfii was originally found by Kurth in the intes- 
 tinal canal of fowls, and then cultivated partly in gelatine partly 
 in suitable watery solutions. In the fresh substratum the Bac- 
 terium vegetates at first in the rod-form. In the gelatine the 
 rods continue united together into large filaments often twisted 
 
1 III.] 
 
 A rthrosporous Bacteria. 
 
 into a coil ; in the fluid short and motionless filaments are 
 formed only at a temperature of more than 35 C. ; at 20 C. the 
 filaments separate into motile rods. At the close of their vege- 
 tation when the substratum is exhausted, the rods fall asunder 
 
 Fig. 3- 
 
 into short roundish cells, and these again may be termed spores 
 since in a fresh substratum they develope into new rods or 
 filaments. 
 
 Though their course of development is more complex yet the 
 phenomena observed in Crenothrix, Cladothrix, and Beggiatoa, 
 if ZopPs description is correct, closely resemble those just de- 
 scribed. They will be noticed again below in Lecture VIII. 
 
 Fig. 3. Leuconostoc mesenterioides, Cienkowski. a sketch of a Zoogloea. 
 b section through a full-grown Zoogloea just before the commencement of 
 spore-formation, c filaments with spores from an older specimen. 
 d isolated ripe spores, e-i successive products of germination of spores 
 sown in a nutrient solution ; sequence of development according to the 
 letters. In e the two lower specimens show the fragments of the ruptured 
 spore-membrane on the outer surface of the gelatinous envelope indicated by 
 dark strokes, i portion of a gelatinous body from h broken up into short 
 members, which have been separated from one another by pressure. After van 
 Tieghem (Ann. d. sc. nat. ser. 6, vii). a natural size, b-i magn. 520 times. 
 
24 Lectures on Bacteria. [$ iv. 
 
 Examples of the other and simpler kind of arthrosporous forms 
 are to be found, according to our present knowledge, in the 
 forms described under the name of Micrococcus 
 (Fig. 4). Each vegetative cell may at any moment 
 begin to form a new series of vegetative cells ; there 
 is no distinction between specifically reproductive 
 F ' 1 S- 4- and vegetative cells. 
 
 The entire distinction between endosporous and arthro- 
 sporous Bacteria is required by the present state of our know- 
 ledge. It remains to be seen whether and to what extent it will 
 be maintained. Our knowledge is at present still so incomplete 
 that we must on the one hand regard the discovery of endo- 
 genous formation of spores as possible or probable in forms 
 where they are hitherto unknown, even in the simplest Micro- 
 cocci, and I say this to prevent all misunderstanding; and on 
 the other hand we cannot say that facts will not come to light 
 in course of time which will do away with any sharp separation 
 between the two divisions. 
 
 IV. 
 
 Species of Bacteria. Distinct species denied. The 
 grounds for this denial insufficient. Method of in- 
 vestigation. Relationships of the Bacteria and their 
 position in the system. 
 
 HAVING now made ourselves acquainted with the course of 
 development in Bacteria in its main features, we proceed to 
 consider the much-debated question whether there are specifi- 
 cally distinct forms, species of Bacteria, as these terms 
 are used in descriptive natural history, and how many such 
 species can be determined. Species are determined by the 
 course of development. By the term species we mean the sum 
 
 Fig. 4. Micrococcus Ureae, Cohn, from putrifying urine. Single cells 
 and cells united in rows (= Streptococcus). Magn. noo times. 
 
5 iv.] The question of species. 25 
 
 total of the separate individuals and generations which, during 
 the time afforded for observation, exhibit the same periodically 
 repeated course of development within certain empirically deter- 
 mined limits of variation. We judge of the course of develop- 
 ment by the forms which make their appearance in it one after 
 another. These are the marks by which we recognise and dis- 
 tinguish species. In the higher plants and animals we are 
 in the habit of taking the marks chiefly from a single section of 
 the development, namely, from the one in which they are most 
 distinctly shown. We distinguish birds better by their feathers 
 than, for instance, by their eggs. This abbreviated method of 
 distinguishing is convenient, wherever one section of the de- 
 velopment is so pregnant as to make the consideration of the 
 rest unnecessary. But this is not always the case. The simpler 
 the forms of an organism are, the larger must be the portions 
 of development requisite for characterising and distinguishing it, 
 and the demand is still greater when we have to compare the 
 entire course of the development of the species, to use the same 
 figure, from the ovum of the first to the ovum of the next gene- 
 ration. We are pleased if we succeed in this way in finding any 
 single mark to serve our purpose, but we must not be too con- 
 fident of finding one. 
 
 Experience has taught us that different species may behave 
 very differently in respect of the forms which make their appear- 
 ance successively in their course of development. In some the 
 same forms constantly recur one after another with comparatively 
 small individual variations. These may be termed monomorphic 
 species. Most of the common higher plants and animals are 
 examples of this, and also many of the lower and simpler kinds. 
 They can be readily distinguished after a little experience even 
 by single portions from the general development. We can re- 
 cognise a horse-chestnut, for example, by each individual leaf 
 plucked from the tree. 
 
 Other species are pleomorphic and may appear in very 
 unlike forms even in the same segments of the development, 
 
26 Lectures on Bacteria. [ iv. 
 
 partly from the effect of external causes which are known and 
 may be varied at pleasure in our experiments, partly from 
 internal causes which cannot at present be analysed. The 
 white mulberry-tree, for example, in contrast to the horse- 
 chestnut just mentioned produces foliage-leaves very unlike each 
 other and with no certain rule of succession, some simply cor- 
 date, others deeply notched and lobed. We should not recog- 
 nise the species by a leaf of the latter kind, if we had before 
 only happened to have seen the cordate leaves. This occurs 
 frequently and to a still greater extent in the lower plants, 
 though they need by no means belong, like the Bacteria, to the 
 simplest and smallest forms. Many of the larger Fungi, for ex- 
 ample, the forms of Mucor,and green Algae, such as Hydrodictyon 
 and the remarkably pleomorphous Botrydium granulatum, exhibit 
 phenomena of this kind in a very striking manner, especially 
 when it further happens, as it often does happen in similar 
 plants, that the successive members of the development do 
 not continue in prolonged connection with each other, like the 
 leaves of the mulberry, but separate and vegetate apart from 
 one another. In this case if we happen to find the objects 
 separate and alone, and are accustomed from our experience 
 of the chestnut always to judge of a species by the individual 
 form, we fall into mistakes such as the history of botanical study 
 can supply in great abundance. But if we observe how each 
 form developes and how it originated, we perceive that they 
 have all the same course, the same origin, and the same return 
 to similar beginnings, or as we may say, conclusions of the 
 development. 
 
 The pleomorphous species therefore differ from the relatively 
 monomorphous species only in the greater number of forms 
 and in the greater amount of differentiation in the course of 
 development; the qualities of the species are apportioned in 
 equal measure in the one as in the other. 
 
 As regards then the species of Bacteria two views have been 
 promulgated, which in their extreme form differ much from one 
 
$ iv.] The question of species. 2 7 
 
 another. According to the one view their case is the same as 
 that of all organisms other than Bacteria, that is, of all other 
 plants and animals ; like these they are distinguished into 
 species. This was accepted as a matter of course by the earlier 
 observers from the first discovery of the Bacteria by Leeuwen- 
 hoek (3), to the more careful and extended observations of these 
 organisms which was undertaken by Ferdinand Cohn (4) at the 
 beginning of the period from 1860 to 1870. Cohn, following 
 in the steps of his predecessors, especially Ehrenberg (5), en- 
 deavoured to give a general view and classification of the forms 
 which had become known to himself and others. It was im- 
 portant to arrange the material in hand and waiting further ela- 
 boration in some provisional manner, and to do this it was 
 either allowable or necessary to start from the assumption, 
 which certainly required to be proved, that a species was always 
 characterised by a definite form, as is the case with the above- 
 mentioned comparatively monomorphous kinds. The species 
 were therefore distinguished by their shape and growth-form, with 
 some help from their effects on the substratum, and then further 
 classified. The names Coccus, Spirillum, Spirochaete, &c., applied 
 above to growth-forms corresponding to such terms as tree and 
 shrub, were used as names for definite natural genera like birch, 
 chestnut, &c. ; such genera we may accordingly therefore term 
 form-genera. Whether these form-genera and form-species did 
 or did not really coincide in all points with natural genera and 
 real natural species, was expressly left undecided by Cohn and 
 reserved for further investigation. 
 
 Cohn's view as expressed in his provisional classification was 
 opposed by other writers, who went so far as to deny that there 
 were any species of Bacteria. They considered that the ob- 
 served forms proceeded alternately from one another, the one 
 being convertible into the other with a change in the conditions 
 of life, and that this change might be accompanied by a corre- 
 sponding change in the effects on the substratum, though this 
 point does not, strictly speaking, belong to the subject which we 
 
28 Lectures on Bacteria. [$ iv. 
 
 are considering. Full expression was given to this view by 
 Billroth (6) in 1874 in a lengthy publication, in which he includes 
 all the forms which he had examined, and they were many and 
 various, in one species which he names Coccobacteria septica. 
 N'ageli (7) and his school have supported the same views since 
 1877. Nageli indeed expresses his opinion on the one hand 
 with circumspection and reserve, saying that he finds no necessity 
 for separating the thousands of Bacterium-forms which have come 
 under his observation even into two species, but that it would be 
 rash to speak decidedly on a subject that is so imperfectly ex- 
 plored. On the other hand he goes so far as to say : If my view 
 is correct, the same species in the course of generations assumes 
 a variety of morphologically and physiologically dissimilar forms 
 one after another, which in the course of years and decades 
 of years at one time turn milk sour, at another give rise to 
 butyric acid in sauerkraut, or to ropiness in wine, or to putrefac- 
 tion in albumen, or decompose urine, or impart a red stain to 
 food-material containing starch, or produce typhus, relapsing 
 fever, cholera, or malarial fever. 
 
 In presence of this statement of opinion our practical interests 
 require that we should obtain a decided answer to the question 
 of species which we are here considering, for it certainly is not 
 a matter of indifference in medical practice, for example, 
 whether a Bacterium which is everywhere present in sour milk 
 or in other objects of food, but without being injurious to health, 
 is capable or not of being changed at any moment into a form 
 which produces typhus or cholera. The scientific interest cer- 
 tainly demands that the question should be set at rest. 
 
 It may safely be maintained that continued investigation has 
 at length arrived at a decision and it is this, that there is no 
 difference as regards the existence of species and their deter- 
 mination between this and any other portion of the domain of 
 Natural History. 
 
 Species may be distinguished provided we follow the course 
 of development with sufficient attention. Some which are 
 
$ iv.] The question of species. 29 
 
 familiar to us through the researches of Brefeld, van Tieghem, 
 Koch, and Prazmowski are comparatively monomorphous ; they 
 make their appearance in the vegetative segments of their de- 
 velopment as a rule in the same forms as regards their shape, 
 growth and grouping. Others show a greater amount of 
 variation in these respects; they display the phenomena of 
 pleomorphy in varying degrees. Among the endosporous 
 Bacilli described above Bacillus Megaterium is a particularly 
 good example of monomorphy. A motile rod is developed from 
 the spore and gives rise as it grows to successive similar gene- 
 rations of rods, until these at length proceed to the formation of 
 fresh spores (Fig. i). 
 
 Bacillus subtilis when growing normally in a fluid differs to 
 some extent from B. Megaterium; successive generations of 
 rods moving about in the fluid proceed from the germinating 
 spores, but the later generations which proceed from them re- 
 main united into long filaments and are without motion, being 
 grouped together and forming on the surface the Zoogloea- 
 membrane mentioned on page 12. In this state they then form 
 fresh spores. Here therefore we have a small amount of 
 pleomorphy, two, or reckoning the spores, three distinct forms, 
 and in a sequence also which is regularly repeated from one 
 spore-generation to another. Moreover the special conditions 
 of shape and size always remain the same within certain limits 
 of variation, for variations in the direction indicated certainly 
 occur in this case as they do everywhere in the organic world. 
 Stunted forms may also be met with. I have for instance re- 
 peatedly observed some of the rods in a group of Bacillus 
 Megaterium, in circumstances unfavourable to its nutrition, sepa- 
 rate into its cells which were themselves already short, and these 
 cells round themselves off and in this way represent what may 
 be termed Cocci. Other unusual forms also made their appear- 
 ance with the Cocci. There was scarcely any or no formation 
 of spores. Under improved food-conditions these stunted forms 
 reverted to the normal state. 
 
30 Lectures on Bacteria. [^ iv. 
 
 The arthrosporous species, Crenothrix and Beggiatoa, which 
 have been mentioned above, are particularly striking examples 
 of pleomorphous species, if the accounts of them which we 
 possess are correct (see Lecture VIII). But it is in these very 
 forms that the course of development, as we have already pointed 
 out, has not been so completely followed out and so clearly ex- 
 plained as to exclude the possibility, that the apparently irregular 
 pleomorphism is due in these cases to the admixture sometimes 
 of several less pleomorphous species. And even if we accept very 
 extreme statements with regard to Bacteria, it is nevertheless 
 true that the most pleomorphous Bacteria show a very high 
 degree of uniformity when compared with the lower plants 
 mentioned on page 26, such as Botrydium, Hydrodictyon, and 
 many others. 
 
 Any one not familiar with the subjects and investigations in 
 question will be inclined to ask how there can be such a pro- 
 found difference of opinion as that between the negation and 
 affirmation of the existence of species in Bacteria. The answer 
 is, that the difference has its origin in the differences and to 
 some extent in the mistakes in the method of investigation. I 
 do not use the word method here in the customary sense of 
 manual skill and practical contrivances in investigation, but to 
 express the course of procedure in examining and judging of 
 the observed phenomena. 
 
 Species, as is acknowledged and as has been already pointed 
 out above, can only be determined and recognised in and 
 through the course of development, and this consists in the suc- 
 cessive development of forms, one from another. The forms 
 which appear later in the series proceed from the earlier forms, 
 as parts of them, and are therefore at every moment in un- 
 broken continuity with them, even when subsequently separated 
 from them. The proof that they all belong to one and the 
 same course of development can only therefore be established 
 by proving this continuity. The attempt to establish it in any 
 other way, for example, by ever so careful observation of the 
 
$ iv.] The qitestion of species. 3 1 
 
 forms which make their appearance one after another at the 
 same spot, or by the construction of a hypothetical series of de- 
 velopments by the most exact and ingenious comparison of 
 these forms, involves a logical fallacy. We distinguish, for in- 
 stance, a species of wheat by its seed, its stem and leaves, its 
 flowers and fruits, and we know that these proceed alternately 
 from one another ; but the latter fact we know only by ob- 
 serving that the one of these members arises as part of one of 
 the others, and by observing also how this happens. This is 
 the only reason why we consider the grain of wheat to belong 
 to the wheat-plant, whether it is attached to it or has fallen to 
 the ground or lies thrashed out on the floor of the granary. 
 That the stem with the leaves belongs to the grain we know by 
 observing its origin as part of the grain, not because we have 
 seen wheat-plants growing where wheat was sown ; weeds may 
 grow at the same spot along with the wheat. 
 
 This mode of viewing the matter sounds trivial ; its truth will 
 seem obvious to every one, and rightly so ; and yet it cannot be 
 too often repeated, for the logic which it is intended to illustrate 
 is being constantly disregarded, and a mass of confusion has 
 been the result of this neglect. This may be shown by means 
 of the very example which we have chosen, for less than fifty 
 years ago it was maintained that all sorts of weeds were pro- 
 duced from the seed of the wheat-plant, and people (8) in other 
 respects well-educated and intelligent believed that this was 
 possible, because these weeds sprang up in the spots where 
 wheat had been sown. But whoever examines at the right place 
 finds that either wheat or nothing grows from the wheat-grain, 
 that the weed springs only from the seed of the species of 
 weed which may happen to be present, and that where 
 the weed grows up instead of or with the wheat, its seed has 
 found its way by some means to the place where the wheat 
 was sown. 
 
 Notions and mistakes like these in the case of the wheat- 
 plant have appeared again and again in connection with smaller 
 
32 Lectures on Bacteria. [$ iv. 
 
 organisms, such as Algae and Fungi, both those of the larger 
 kinds and the microscopically minute. The separate species 
 were imperfectly known, and different ones were brought into 
 genetic connection with one another, because observation of 
 continuity was omitted or imperfectly made, and in its place was 
 substituted the observation of the succession in time of forms 
 at the same spot, or the comparison of them as they made their 
 appearance there together. 
 
 The smaller and simpler the forms, the greater certainly is 
 the difficulty of satisfying our logical demand, and the greater 
 the attention which must be paid to it. In small forms consist- 
 ing of isolated cells of no very marked shape, such as some of 
 the lower Fungi and the Bacteria, we must observe carefully 
 whether the sowing contains the germs of a single species or of 
 several mixed together. The latter is very frequently the case, 
 as experience shows. Various species often occur together and 
 mixed with one another at the spots from which the material 
 for the observation was obtained ; during the investigation forms 
 not desired, ' unbidden guests/ may find their way with par- 
 ticles of dust into the material, and even when we are dealing 
 with apparently quite pure material, a small quantity of micro- 
 scopic weeds, as we may say in this case also, may be mingled 
 with it. 
 
 If every thing in the mixture grows at an equal rate, the 
 different species may be kept distinct with comparative ease, and 
 the character of the mixture is clearly understood. But the state 
 of things may be different from this, and experience shows that 
 it often is different. The one species develops vigorously under 
 the existing conditions, the other feebly or not at all ; the more 
 successful species gains the upper hand of the less successful, 
 dispossessing it and even entirely destroying it. Further ex- 
 amination shows that in some cases a weed has grown up in 
 place of the wheat. This may very easily happen. We shall 
 see further on that some Bacteria, for example, double the num- 
 ber of their cells under favourable conditions in less than an 
 
$ iv.] The question of species. 33 
 
 hour. Those to which the conditions are unfavourable may be 
 seen, if a single specimen is watched continuously, to be dis- 
 solved and to disappear entirely in a few hours. By the com- 
 bination of phenomena of this kind the character of any given 
 mixture may be totally changed in a short space of time. 
 
 It is obvious that difficulties such as these do not invalidate 
 our postulate, but on the contrary bring it out into sharper 
 relief. Those who altogether deny the existence of species in 
 Bacteria, with Billroth and Nageli at their head, have in fact 
 never undertaken a direct observation of continuity of develop- 
 ment, and they are therefore not justified in denying their exist- 
 ence. Billroth has accurately examined and compared the 
 forms, but has never continuously followed and checked the 
 changes in a preparation or culture ; the observation has been 
 interrupted by intervals of sufficient length to allow of various 
 things happening unobserved. Nageli, as far as can be gathered 
 from his publications, has not closely examined the forms at all, 
 but grounds his conclusions, even when they are morphological, 
 on non-morphological observations with respect to phenomena 
 of decomposition on the great scale. One instance of this mode 
 of dealing with the subject may be mentioned. Nageli remarks 
 that milk which has not been boiled turns sour when left standing 
 for a time, but that boiled milk becomes bitter (9). He admits 
 that the sourness is due to the presence of a Bacterium. He 
 considers the bitterness to be the result of a change in the 
 action of the same Bacterium caused by the boiling a ' trans- 
 formation of the definite ferment-nature of a single Fungus into 
 a ferment of another kind.' Here it is assumed that a single 
 Bacterium-species is present in the unboiled milk ; the question 
 is not asked whether there may not perhaps be several species in 
 it, some of which predominate before, the others after the boil- 
 ing, and whether the different changes in the milk may not be 
 thus explained. But Hueppe's more recent researches have 
 shown that such is really the true state of the case (10). Of the 
 various Bacteria-forms present in the unboiled milk, Micrococcus 
 
34 Lectures on Bacteria. [$ iv. 
 
 lacticus is at first most active at a low temperature, and turns the 
 milk sour by the formation of lactic acid ; it is killed by boiling, 
 but the spores of Bacillus Amylobacter, the Bacillus of butyric 
 acid, which is also present in the milk retain their vitality, and 
 this Bacillus causes the decompositions in boiled milk which 
 give it a bitter taste. 
 
 Another instance of the same kind is the statement ema- 
 nating from Nageli's laboratory, that the hay-bacillus, Bacillus 
 subtilis, is identical with Bacillus Anthracis, the Bacillus of 
 anthrax. The two species are very like each other, and Buch- 
 ner' s observations certainly contain some true remarks about 
 them, which will be discussed in Lecture XII. But the most 
 striking characteristic of B. subtilis is the often-described ger- 
 mination of its spores, the growing out of the germ-cell from 
 the transverse fissure of the spore-membrane at right angles to 
 the longitudinal axis of the spore. The Bacillus of anthrax 
 does not exhibit this phenomenon, as Buchner himself tells us. 
 But due regard has nowhere been paid to these differences, so 
 that it is still doubtful whether Buchner has examined B. subtilis 
 at all. In this case too the morphological statement is without 
 certain foundation and justification. 
 
 The increased attention bestowed by observers on this subject, 
 beginning with the wheat-plant and going down through various 
 larger forms of the lower plants to Bacteria, has done away 
 one after another with the erroneous notions indicated, and led 
 to the general adoption of the view above explained, that ques- 
 tions of species are essentially alike throughout the series of 
 organisms. In the case of the Bacteria much still remains to 
 be done ; our knowledge of these is yet only in its infancy. 
 
 I say that increased attention is leading to this result. I 
 should wish at the same time to point out once more the con- 
 ditions which have been and which are of the first importance. 
 As might be expected, the aids to investigation, apparatus, tech- 
 nical methods, reagents, &c., have been improved. To deter- 
 mine the questions which we are at present considering, minute 
 
$ iv.] The question of species. 35 
 
 organisms have to be isolated and unceasingly watched in order 
 to see what proceeds from the single individual, if it developes. 
 This end can only be obtained by means of cultures which can 
 be followed with exactness under the microscope. A spore or 
 rod in the preparation must be permanently fixed under the 
 microscope, and the phenomena of its growth must be observed 
 without interruption. This is done by help of the moist 
 chamber, a contrivance in which the microscopic object pro- 
 tected from desiccation can be observed continuously under con- 
 ditions favourable to vegetation. There are several varieties of 
 apparatus of this description, which have their advantages and 
 disadvantages according to the special case and also to the 
 habits of the observer, but we must not enter into a detailed 
 description of them here. 
 
 Fluids are usually employed as the medium in which the ob- 
 ject is placed for microscopic observation and for culture, on 
 account of their transparency. Living and especially moving 
 objects readily change their position in a fluid and become 
 mixed together. A method which greatly assists the fixing of 
 an object where continuity of observation is required, consists in 
 the use of a transparent medium which allows of the conditions 
 necessary to vegetation, and is soft but not fluid, so that dis- 
 placement of the objects and disturbance of the observation are 
 more or less perfectly avoided. Such media are gelatine and 
 similar substances, especially the gelatinous substance known 
 in commerce as agar-agar and prepared from sea-weeds of 
 the Indian and Chinese seas. Gelatine, as I understand, was 
 first employed by Vittadini in 1852 in the culture of micro- 
 scopic Fungi (11), and has been frequently used since that time, 
 especially by Brefeld. Klebs more recently in 1873 (12) re- 
 commends it specially for the cultivation of Bacteria ; cultures 
 of these organisms have been conducted in recent times in a 
 gelatinous substratum, especially by Koch. 
 
 Having thus glanced at the morphology and the history of the 
 development of Bacteria, we have still to enquire what is their 
 
 D 2 
 
36 Lectures on Bacteria. [ iv. 
 
 position in the organic world and their natural affinity to other orga- 
 nisms. The question is of only secondary interest to us on the 
 present occasion, and must not therefore be examined at any length. 
 
 If we compare the structure and development of Bacteria with 
 those of other known creatures, as we must do to answer the 
 above question, the arthrosporous Bacteria are seen to agree 
 entirely in all essential points with the members of the plant- 
 group of Nostocaceae in the wider sense of the word ; only 
 the Nostocaceae are furnished with chlorophyll in conjunction 
 with another blue or violet colouring matter which is soluble 
 in water, and are thus distinguished from the Bacteria which 
 contain no chlorophyll. There is no reason why the arthro- 
 sporous Bacteria should not be termed Nostocaceae which 
 are devoid of chlorophyll. Structure, growth, occasional for- 
 mation of Zoogloeae, more or less constant motility, especially 
 developed in the Oscillatorieae, a division of the Nostoca- 
 ceae, are the same in the two groups, so that apart from the 
 absence of chlorophyll there is no greater difference between 
 them than between the separate species of either of the groups. 
 This may be illustrated by the case of Leuconostoc described 
 on page 22. The name indicates that the plant entirely re- 
 sembles in all respects the bluish-green species of the genus 
 Nostoc which live in water and on moist soil, only it is colour- 
 less and white. To this may be added, that most of the 
 Nostocaceae attain to considerably larger dimensions than the 
 Bacteria in their cells and in the aggregations of their cells, and 
 that the members of the group which resemble the Bacteria are 
 related to other forms of a more varied and higher differentia- 
 tion and conformation. 
 
 The Bacteria which we have distinguished as endosporous 
 entirely resemble the arthrosporous Bacteria in every respect ex- 
 cept the peculiar formation of spores, and resemble no other 
 known organisms. We must therefore place them next to the 
 arthrosporous division, at least for the present and in accord- 
 ance with our present knowledge. 
 
$ v.] Origin and distribution. 37 
 
 Hence the Bacteria have been arranged in one group with 
 the Nostocaceae, and this group has received the name of 
 Fission-plants or Schizophytes ; the Nostocaceae which contain 
 chlorophyll are Fission-algae, those which have no chlorophyll 
 are Fission-fungi. 
 
 The entire group of the Schizophytes is somewhat isolated in 
 the general system ; a closer association with other groups can- 
 not be established at present, and it would lead us too far away 
 from our more immediate subject to enter further into the con- 
 jectures which may be formed about them. So much however 
 is beyond doubt, that most Schizophytes, the Nostocaceae 
 especially, have all the characteristics of simple plants. They 
 show a very slight approximation to the Fungi, in the sense in 
 which that term is used in the natural system, as has been 
 already stated in the Introduction. We can only say therefore 
 that the Bacteria, together with the rest of the Schizophytes, are 
 a group of simple plants of a low order. 
 
 The old observers regarded them as belonging to the animal 
 kingdom and to the group of Infusorial Animalcules, chiefly on 
 the ground of their motility and in the absence of the basis re- 
 quired for a more exact comparison. At present there is no 
 reason for separating them from the vegetable kingdom, though 
 it is merely a matter of convention in the case of these simple 
 organisms where and how we should draw the line between the 
 vegetable and animal kingdoms. 
 
 V. 
 
 Origin and distribution of Bacteria. 
 
 WE commenced our survey of the mode of life of the Bacteria 
 by explaining in what manner and from whence they make their 
 way to the spots where we find them. 
 
 If we adhere to the general result of the foregoing con- 
 siderations, namely, that Bacteria are like other vegetable growths, 
 
38 Lectures on Bacteria. [ v. 
 
 we may at once assume that their origin is the same as that 
 of other plants, that is, that the Bacteria existing at any given 
 time have sprung from beginnings which proceeded from in- 
 dividuals of the same species, and experience shows that this 
 is really the case. These beginnings may be spores or any 
 other cells capable of life; we shall here usually call them 
 germs. 
 
 The germs of living beings, especially plants, are extra- 
 ordinarily numerous. They may be said to cover the surface 
 of the earth and the bottom of the waters with an infinite 
 profusion of mingled forms. The number of plants observed 
 in the developed state gives no idea or only a very imperfect 
 idea of this fact, because a much larger number of germs is in 
 all cases produced from a single plant than can arrive at their 
 full development in the space at their command, which is in 
 fact always limited. The smaller the organisms are, the greater 
 advantages they enjoy as a general rule caeteris paribus for the 
 production and distribution of their germs, for it is so much 
 easier for them to find space and a sufficient quantity of food for 
 their development and for the production of new germs; the 
 mechanical conditions for the transport of the germs from place 
 to place are also more favourable in proportion as the volume 
 and mass are diminished. For these reasons the number and 
 distribution of the germs of lower microscopic organisms, espe- 
 cially in the vegetable world, must seem astonishingly great to 
 any one who is unprepared for the facts. If spring-water is 
 allowed to stand in a glass, it becomes green in time from the 
 growth of small Algae, whose germs were present in the water 
 before it was placed in the glass or have been carried there with 
 particles of dust. If a small piece of moistened bread is placed 
 in the water a growth of mould soon makes its appearance, pro- 
 ceeding from germs of Mould-fungi. Some time since I made 
 researches with a different object into the Saprolegnieae, a 
 group of rather large Fungi consisting of about two dozen 
 well-known species, which grow in water on the bodies of 
 
$ v.] Origin and distribution. 39 
 
 dead animals, and it was found that germs of one or several 
 species of this single group were present in every handful of 
 mud from the bottom of every sheet of water from the sea-level 
 to a height of 2000 metres. The actual presence of the germs 
 may be shown in all these cases by microscopic and experi- 
 mental examination, to the conduct of which we will recur 
 presently. 
 
 As these facts again would lead us to expect, among micro- 
 scopic growths some are rare and some are common, some 
 have a limited and some a very extensive area of distribution. 
 The principle must be the same with these as with the higher 
 and larger organisms ; climatic and other external causes must 
 have a similar effect on the distribution, though for the reason 
 stated above that effect is generally less powerful than in larger 
 and more pretentious forms. The researches into this subject 
 are not yet extensive enough to permit of the production of 
 many details. But we know, for example, that a small Fungus, 
 scarcely visible to the naked eye, Laboulbenia Muscae, which 
 vegetates on the surface of the bodies of living house-flies in 
 Vienna, and which appears to be common in southern Europe, 
 does not occur in the middle and west of Europe ; at all events 
 after careful search it has not yet been found. Instances 
 of the reverse kind are more numerous. Our common species 
 of moulds, Penicillium glaucum, for example, and Eurotium, 
 are spread over all parts of the world and all climates, and the 
 same is the case with other small Fungi and Algae. 
 
 In this point also Bacteria are only special instances of the 
 series of phenomena which have been shown above to occur 
 as a rule in small organisms. Our knowledge of the several 
 species, as appears from preceding lectures, is too imperfect to 
 enable us to make precise statements with respect to the larger 
 number of them ; at the same time we know that some species 
 are comparatively rare, such as Micrococcus prodigiosus and 
 Bacillus Megaterium, while others, like B. subtilis, B. Amy- 
 lobacter, and Micrococcus Ureae, occur in almost every situation 
 
4O Lectures on Bacteria. [ v. 
 
 in which they find the conditions of vegetation, which are them- 
 selves of very common occurrence. We shall make acquaint- 
 ance with other illustrative instances in subsequent special 
 discussions. Dispensing with an exact determination of the 
 species in every case, we shall be perfectly safe in declaring, 
 as the result of direct observations, that the vital germs of 
 Bacteria are scattered abroad with such profusion in earth, air, 
 dust, and water, that their appearance at all spots where they 
 find the conditions* necessary for vegetation is more than 
 sufficiently explained. 
 
 The way to prove this, and at the same time to determine 
 approximatively the number of germs within a given space, is ob- 
 viously the same in the case of the germs of Bacteria as in that 
 of other lower organisms, Fungi and others; both necessarily 
 come under our observation at the same time, when they are 
 present. It consists first of all and simply in microscopical 
 examination. But in this method we encounter considerable 
 difficulties. Sometimes the germs are not present in every 
 smallest spot ; they must be sought for, and this is at all times a 
 troublesome process, especially when it is intended to count them. 
 Various devices may it is true be applied to lighten this labour. 
 Pasteur (13), for example, employed an ingenious contrivance 
 for finding germs in the air in the form of a suction-apparatus, 
 an aspirator, which drew in the air through a tube stopped with 
 a dense plug of gun-cotton. The plug allows the air to pass, 
 while the solid substances in suspension in the air and the 
 germs therefore with them are caught on or in the plug. The 
 quantity of air passing through the apparatus within a given 
 time can be easily determined. The gun-cotton is soluble in 
 ether, and by taking advantage of this property the germs which 
 have been intercepted in the plug may be obtained suspended 
 in a clear solution, and collected within a narrow space for ex- 
 amination and even for counting. 
 
 But in this process the germs are very liable to be killed by 
 the ether, and even in ordinary microscopical examination it is 
 
$ v.] Origin and distribution. 41 
 
 impossible to be quite certain whether we are dealing with dead 
 or with living objects. Yet it is a matter of the first importance 
 to determine whether germs capable of development are present 
 or not, and this would require further and very complex modes 
 of procedure. 
 
 Hence various other methods have been tried with the object 
 of making the investigation easier and more trustworthy in both 
 directions. It was Koch who at length cracked the egg, like 
 Columbus. Starting from the empirical fact that gelatine, com- 
 bined with other nutrient substances easily prepared and in a 
 state of solution, is a very favourable substratum for the develop- 
 ment of most Fungi that are not strictly parasitic, and also 
 of Bacteria, he distributes quantities of the substances intended 
 for examination, earth, fluids, &c., in properly prepared gelatine, 
 liquefying at a temperature of about 30 C., and then makes the 
 gelatine stiffen by lowering the temperature. The quantities 
 may be exactly determined. Each germ is fixed in the 
 stiffened mass and so developes, and the products of the 
 development are at least at first also fixed and not liable to 
 displacement in the medium. If the transparent gelatine is 
 spread in a thin layer on glass slides at the commencement of 
 the investigation, the germs and the products of their develop- 
 ment can be found with certainty with the microscope, and if 
 necessary be counted. If the object is to examine the air, the 
 best plan is to draw it in slowly by means of an aspirator 
 through glass tubes, coated inside with a layer of gelatine. If 
 the stream is properly regulated, the greater part at least of the 
 germs which are mixed with the air sink downwards and are 
 caught in the gelatine, where they may then undergo further 
 development. If experiments of this kind are properly con- 
 ducted and disturbing impurities excluded, distinct groups of 
 Bacteria, Fungi, &c., will be found after a few days in the 
 gelatine. Each group originates in a germ, or in some cases in 
 an assemblage of germs, which made .its way to the particular 
 spot at the commencement of the experiment, as may often 
 
42 Lectures on Bacteria. [ v. 
 
 be easily ascertained by direct observation. It is obvious that 
 the purpose under consideration can be most certainly and most 
 simply effected in the way which has just been described. The 
 result certainly can never be more than approximatively exact, 
 because the nature of the process does not ensure that all the 
 germs capable of development which find their way to the 
 gelatine in the apparatus do in any given case actually develope, 
 or in the case of air-suction that all the germs without exception 
 are always actually caught. No other method which has not 
 this fault in an equal or even greater degree and without the 
 advantage of fixing the germ has up to the present time been 
 devised, nor is it easy to imagine one that would be practicable. 
 It may be added here that Koch's method has the further 
 advantage of making the sorting and selection of Bacteria for 
 isolated culture comparatively easy. Each of the groups derived 
 from a single germ in the experiments above described must 
 contain a single species without admixture. To obtain a 
 quantity of this species for a pure culture we have only to remove 
 a sample from the group with the needle. To sort a mixed mass 
 of Bacteria requires simply the spreading small quantities of it 
 over a large amount of gelatine, and thus isolating germs capable 
 of development. The groups formed from these germs supply 
 pure species-material. Various other experiments have been 
 tried with the same objects and on the same principles, but with 
 less perfect arrangements and methods ; we must not, however, 
 enter here into a more detailed account of them. The most 
 elaborate are those instituted by Miquel and continued from 
 year to year in the meteorological observatory at Montsouris, 
 near Paris, intended especially to ascertain the distribution of 
 germs in the air and in water (15). 
 
 All researches hitherto conducted have given the general 
 result described above, and a further one which might have 
 been expected beforehand, namely, that the number of germs 
 capable of development v.aries, other conditions being the same, 
 with the place, the time of year, the weather, and other circum- 
 
v.] Origin and distribution. 43 
 
 stances. To give some idea of the approximate numbers it may 
 be added, that the number of germs in the air caught on glass 
 plates in a mixture of glycerine and grape-sugar in the aspirator, 
 Fungi and Bacteria capable of development and in some cases 
 dead being taken together, varied in the garden of Montsouris, 
 in a single series of observations, from between 0-7 to 3-9 in 
 December and to 43-3 in July in a litre of air. 
 
 The most exact air-determinations have been recently carried 
 out by Hesse with the aspirator and gelatine-process. These 
 showed the presence of germs capable of development in a litre 
 of air, as follows : 
 
 In Sick-ward No. i, with 17 beds, Bacteria 2-40, Moulds 0-4. 
 2, 18 n-o, i-o. 
 Cattle-stall for experimental pur- 
 poses belonging to the Na- 
 tional Office of Health : (a) 58-0, 3-0. 
 
 W 2 3 2 '> 28 '- 
 
 The air out of doors in Berlin was found to contain o- 1-0-5 
 
 germs per litre, of which about half were Fungi and half 
 Bacteria. 
 
 Miquel obtained thirty-five germs per cubic centimetre in 
 rain-water caught as it fell, sixty-two in river-water from the 
 Vanne; in that from the Seine above Paris 1400, below 
 Paris 3200. 
 
 We have no numerical determinations of the number of germs 
 present in the soil; but we can produce growths of Fungi and 
 Bacteria from every small pinch of soil taken from the surface 
 of the ground. In lower strata, according to some preliminary 
 researches made by Koch (14) in winter, the number of germs 
 capable of development diminishes rapidly. 
 
 A special interest attaches to the question of the presence of 
 germs in and on sound living organisms. That they must remain 
 hanging in profusion to the surface of such organisms is obvious 
 from the preceding statements, and is proved by every investiga- 
 tion. They can penetrate into the interior of the higher forms of 
 
44 Lectures on Bacteria. [$ v. 
 
 plants through the open slits in the epidermis, the stomata, which 
 lead to the system of intercellular passages. It is probable that this 
 actually takes place, but it is not yet quite certain and requires 
 further investigation. The respiratory and alimentary canals in 
 healthy, especially warm-blooded, animals are constantly acces- 
 sible places for the entrance of germs with air, meat and drink, 
 and it is these parts, especially the mouth and the intestinal 
 canal, both in man and other warm-blooded animals, which are 
 as a matter of fact always a well-stocked garden of vegetating 
 Bacteria. They may also make their way into the glands which 
 are in communication with these canals through their excretory 
 ducts. Researches into their occurrence in the blood of healthy 
 living warm-blooded animals give different results. Hensen, 
 Billroth, and other observers maintain their presence there. Very 
 careful investigations by Pasteur, Meissner (13), Koch, Zahn, 
 and others give a negative result; the affirmative result may 
 therefore be due to disturbances and errors in the experiment. 
 But this conclusion is not unavoidable, for a series of experi- 
 ments by Klebs (12) have placed it beyond doubt that both 
 states may occur, and why they may occur. Klebs examined 
 the blood of some dogs, and partly with a negative result. But 
 in the case of one dog the result was affirmative, the fact being 
 that putrefactive Bacteria had been injected into the blood of 
 this animal some time before on the occasion of some other 
 experiments ; it had sickened with them but had quite recovered 
 long before the date of the investigation of which we are now 
 speaking. It cannot be doubted that in this case germs capable 
 of development but actually dormant had remained from the 
 first experiment in the animal's blood, and we may conclude 
 generally that Bacteria germs may be present in healthy blood, 
 if they have once made their way into it through a wound or in 
 some other way. 
 
 The result of the above facts is to show the wide distribution 
 and great abundance of Bacteria-germs, though their species 
 are not at present clearly discriminated. They show also on 
 
$ v.] Origin and distribution. 45 
 
 the other hand that it would be an exaggeration to suppose 
 that these bodies are everywhere present, that is, in every 
 minutest space. Even Pasteur's earlier and famous researches 
 show the inequality of the distribution by extreme examples. 
 This may be briefly illustrated by the following account. A 
 small quantity of germ-free nutrient fluid, very favourable for the 
 development of lower organisms, was introduced into small 
 narrow-necked phials of 1-200 ccm. content ; the air was 
 withdrawn from the phials and the narrow neck hermetically 
 closed. Subsequently the closed neck was reopened by in- 
 tentional fracture of its extremity; air rapidly poured in, and 
 as soon as this had taken place the neck was once more closed. 
 From 1-200 ccm. of air were thus hermetically inclosed in the 
 phial. The germs which they contained were at liberty to develope 
 in the nutrient fluid, which, to use a short expression, remains 
 unaltered if no germs are present. Of ten such phials filled with 
 air in the court-yard of the Paris Observatory not one remained 
 unaltered ; nine out of ten filled in the cellar of the Observatory, 
 which was almost entirely free from dust, and nineteen out of 
 twenty filled at the Montanvert near Chamonix were unaltered. 
 
 The views here expressed with regard to the origin of 
 Bacteria, and especially the fundamental axiom, that they are 
 produced without exception from germs springing from species 
 of the same name, have not been arrived at without trouble or 
 without opposition, and the latter has not entirely ceased even 
 at the present day. We must not pass by the view of the 
 opponents without at least a brief consideration. It may be 
 concisely stated thus : Bacteria may be formed at any moment 
 from parts of other organisms, living or dead ; but it is allowed 
 that they may afterwards multiply by their own growth and also 
 produce their own germs. 
 
 This view is a survival from the old doctrine of original 
 production without parents, spontaneous or equivocal genera- 
 tion. Plants or animals are often known to appear in numbers 
 in places where they had never been seen before, and the super- 
 
46 Lectitres on Bacteria. [ v. 
 
 ficial observer is led to assume in such cases that they owe their 
 origin to other bodies present at the particular place before their 
 appearance there, no matter what these bodies may be, and not 
 to germs formed from similar parents. Such views were not 
 unnatural in ancient times. Virgil's (16) account of the pro- 
 duction of a swarm of bees from the buried entrails of a steer 
 furnishes an obvious illustration, and shows how utterly defective 
 were the observation and reasoning which admitted of such 
 notions. With a closer observation of nature it became evident 
 in one case after another that the appearance of the particular 
 organisms invariably commenced with germs which were the 
 product of parents of the same kind, and that the point not 
 observed was how these germs found their way to the place of 
 observation. Generation without parents was step by step driven 
 into a corner. The process began with large and coarse objects 
 like the maggots of flies which appear in carrion, not by spon- 
 taneous generation, but produced from the ova of flies which 
 have been deposited in it. And as the adherents of the old 
 doctrine were driven back on smaller objects, such as moulds, 
 the lowest forms of animal life and the like, their refutation 
 followed step by step with equal success in these domains also. 
 Microscopic and improved experimental methods by turns 
 sharpened the weapons. Thus we find ourselves face to face 
 with the fact that the adherents of generation without parents, 
 at least during the last hundred years, seek for support to their 
 doctrine always in the minutest and at the time the most inac- 
 cessible objects. The view has never been entirely given up, and 
 for two good reasons. First, because an opinion once expressed 
 or put into print, be it what it may, never totally disappears ; the 
 second and much better reason is, that we must necessarily assume 
 that organisms were certainly once produced without germs and 
 without parents ; the possibility that this may happen again at 
 any time must be allowed, and to prove that this does happen and 
 to show where and how it happens would be highly interesting, 
 and a really worthy subject for the efforts of the enquirer. 
 
$ v.] Origin and distribution. 47 
 
 Bacteria rank with the smallest organisms at present known 
 to us, with the least accessible and the most imperfectly investi- 
 gated. It is true that the question of actual spontaneous gene- 
 ration has been in all essential points decided in the same way 
 in their case as in that of other organisms, by the beautiful 
 researches conducted by Pasteur twenty-five years ago at the 
 instance of the Academy of Paris, and intended to test the 
 doctrine in question in connection with the smallest and least 
 accessible creatures; and every pure and trustworthy investi- 
 gation has confirmed Pasteur's results. Nevertheless there are 
 writers who still hold to the doctrine and who seek for fresh 
 arguments in support of it. A comprehensive theory in this 
 direction is contained in Be*champ's doctrine of Microzymes (17) 
 published twenty years ago. The term Microzyme was applied 
 by him to minute form-elements, such as occur generally 
 in the shape of granules in the protoplasm of animals and 
 plants, and are doubtless formed in them as parts of their 
 substance. If these particles of matter are set free by any 
 cause, especially after the death of the parent, they are supposed 
 to undergo a further process of independent development and 
 to become partly Bacteria, partly also small Sprouting Fungi. 
 They not only outlive the organism which produces them, but 
 enjoy a very prolonged existence extending over geological 
 periods. Close scrutiny of the accounts given by Be'champ in 
 a volume of almost a thousand pages shows no sharp dis- 
 crimination of forms, and no sign that the continuity of the 
 development has been strictly followed, and yet this is a point 
 of the very first importance. The whole matter therefore is 
 without any certain foundation, and is no longer a subject for 
 discussion. 
 
 A. Wigand (18) has quite recently published a preliminary 
 communication, in which he arrives at the same results as 
 Bechamp as regards the question before us. Small portions 
 of living or dead organisms, the latter not being Bacteria, are 
 said to separate from them under definite conditions and to 
 
48 Lectures on Bacteria. [$ v. 
 
 develope into Bacteria. The course of the observations, from 
 which this conclusion is drawn, is in most cases not stated 
 with sufficient exactness to allow of our forming a judgment 
 upon them. Still one observation is mentioned which it was 
 admissible and desirable to have repeated and tested. Wigand 
 states, for the removal ' of all doubt about spontaneous forma- 
 tion of Bacteria in the protoplasm of cells/ that motile Bacteria 
 are found in the living healthy cells of the leaf of Trianea bogo- 
 tensis and in those of the hairs of Labiatae. My attention had 
 been directed to the matter from another quarter before I 
 proceeded to examine into this remarkable statement. Trianea 
 is a South American water-plant, which floats in the manner of 
 our Frogbit (Hydrocharis). If living tissue from the fresh 
 healthy leaf is placed under the microscope, we shall really see 
 in many cells the prettiest representations of the appearance of 
 Bacteria, small slender rods, isolated or attached together in 
 short rows and actively following the movements of the proto- 
 plasm and other cell-contents. An excellent representation, as 
 I said, or model. But a drop of dilute muriatic acid destroys 
 the illusion. The acid at once dissolves the rods in Trianea, 
 which it would not do if they were really Bacteria ; they are 
 simply small crystals of calcium oxalate, which often occur in 
 vegetable cells and in the form of rods. Of the same kind are 
 the much less beautiful rods in the young hairs of the leaf of 
 Galeobdolon luteum and Salvia glutinosa, and so also in other 
 Labiatae or lipped-flowered plants. The case is full of instruction, 
 as showing how a preconceived opinion may lead even good and 
 intelligent observers into the greatest absurdities. I should not 
 otherwise have mentioned it, and I do not think it necessary to 
 go any further into similar matters. Such things at all events 
 are not calculated to weaken the proposition, that according to 
 the observations which actually lie before us even the smallest 
 organisms spring only from germs produced from ancestors of 
 the same kind ; and to this we must hold fast in spite of what- 
 ever may be thought possible or desirable. 
 
vi.] Vegetative processes. 49 
 
 VI. 
 
 Vegetative processes. External conditions : tempera- 
 ture and material character of the environment. Prac- 
 tical application of these in cultures, in disinfection, 
 and in antisepsis. 
 
 IN passing on to the consideration of processes of vegetation, 
 we must first of all remember that agreement in structure and 
 development between Bacteria and other lower organisms neces- 
 sarily implies also an agreement in the chief phenomena and 
 chief conditions of vegetative life. In fact we have simply to 
 do with special cases of phenomena which are of general occur- 
 rence in all living organisms, and which do not differ more from 
 those to be met with in other plants than these do from one 
 another. It is specially true of the Bacteria which do not 
 contain chlorophyll, that their vegetative process agrees essen- 
 tially with that of other vegetable cells which do not contain 
 chlorophyll, both those which belong to the higher plants, and 
 more particularly those belonging to the Fungi. It is to the 
 investigation of the Fungi, which are more easily studied, that we 
 owe much of the advance that has been made in our knowledge 
 of the Bacteria. It is perhaps scarcely necessary to observe 
 that differences prevail from one case to another among Bacteria 
 also as regards the phenomena and conditions of vegetation, 
 analogous with those in the allied groups. 
 
 Our present object, however, is not to give a complete account 
 of everything belonging to the vegetative process, but only to 
 call attention to the points most worthy of notice in connection 
 with the subject of these lectures. The conditions of tempera- 
 ture and the material character of the environment are chiefly 
 to be considered. 
 
 Every process of vegetation is dependent on the temperature 
 of the surrounding medium ; it finds its limits within certain 
 extreme degrees of heat, and its greatest activity at a fixed 
 
 E 
 
50 Lectures on Bacteria. [ vi. 
 
 temperature between these extremes. The cardinal points of 
 temperature are accordingly distinguished as minimum, maxi- 
 mum, and optimum. 
 
 Transgression of the limits leads at first to a cessation of the 
 particular process going on at the time ; other processes may 
 possibly persist. If the raising or lowering of the temperature 
 beyond the maximum or minimum point of vegetation reaches 
 certain extreme degrees, life is destroyed, in other words the 
 death-point is attained. 
 
 In all these respects considerable variations occur in confor- 
 mity with every one's daily experience, according to the species, 
 the state of development, and the character of the environment. 
 
 The limits of temperature in the growth and multiplication of 
 cells are the points which have been chiefly examined in the 
 case of the Bacteria ; it being assumed with some reason that 
 the rest of the vegetative processes, other conditions remaining 
 the same, run proportionally with the growth. 
 
 It appears from the data before us that non-parasitic species, 
 if well and properly nourished, have a tolerably wide range and 
 a high optimum of growth-temperature. The former lies in 
 Bacillus subtilis, for example, according to Brefeld (19), between 
 6C. and 50 C., the optimum being at about 30 C. Bac- 
 terium Termo, Cohn grows between 5 C. and 40 C., while 
 its optimum is 30-35 C. (Eidam 20). Bacillus Amylobacter, 
 according to Fitz (21), has its optimum in solution of glycerine 
 at 40 C., its maximum at 45 C. The minimum of growth, 
 according to present accounts, in Bacillus Anthracis in cultures 
 in gelatine, on potatoes, &c., is at i5C., the maximum at 
 43 C., the optimum at 20-25 C. As a parasite in the blood 
 of rodents it grows at about 4 C. ; at least, not less vigorously 
 than in the optimum just given for specimens under culture. In 
 the Spirillum of Asiatic cholera, according to van Ermengen 
 (see Lecture XIII), the minimum is reached at 8C., the 
 optimum at 37 C., the maximum at 40 C. 
 
 That the species which are more strictly adapted for a para- 
 
vi.] Conditions of vegetation. Temperature. 5 1 
 
 sitic life in warm-blooded animals have a higher maximum and 
 optimum is probable beforehand, and has been proved by Koch 
 (60) in the case of the Bacillus of tubercle, in which the limits 
 of temperature were found to be from 28 to 42 C., and its 
 optimum 3 7-3 8 C. 
 
 The optimum temperature for the formation of spores in 
 endosporous Bacilli, as far as can be ascertained, approaches 
 that of growth. The temperatures for the germination of the 
 endogenetic spores are higher, at least in the case of the op- 
 timum, being 30-34 C., for instance, in Bacillus subtilis, which 
 however also germinates in the temperature of a room which 
 is somewhere about 20 C. B. Anthracis does not germinate, 
 as far as our experience goes, at 20 C. ; the minimum given 
 for this species is 35-3 7 C., the optimum can scarcely be much 
 higher. Other species, as B. Megaterium, grow and germinate 
 quite well at a temperature of about 20 C. 
 
 Transgression of the limits of temperature of vegetation in 
 the downward direction without destruction to life is possible in 
 the case at least of a large number of Bacteria, and to such an 
 extent that in view of the phenomena which are known to occur 
 we may even say that there are no limits. Frisch (22) found 
 the power of development in the forms which he examined, and 
 in their vegetative cells, unaffected when they were frozen in a 
 fluid at a temperature of noC. and afterwards thawed 
 again. Bacillus Anthracis is one of the forms which behave in 
 this manner; in the case of other species the point remains 
 undecided, but it is probable that in some of them the lower 
 death-temperature is higher than this. 
 
 The upper death-temperature, so far as is at present known, 
 is about the same for the vegetative cells of the majority of 
 forms, as for most other vegetable cells, 50-60 C. Similar 
 figures are true also for the spores of arthrosporous forms, 
 though this point requires further investigation. Exceptional 
 cases will be mentioned further on. On the other hand, the 
 endogenetic spores of the Bacilli are capable of enduring 
 
 E 2 
 
52 Lectures on Bacteria. [$ vi. 
 
 extreme high temperatures. Most of them continue capable of 
 germination after being heated in a fluid up to iooC. ; some 
 will bear 105 C., uoC., and as much as i3oC. 
 
 These are all general rules and are not affected by the modi- 
 fications and exceptions which occur in different cases, and 
 which in part depend on the species and individual, other con- 
 ditions remaining the same, in part also are found in the same 
 species, being then dependent on the external conditions, such 
 especially as the length of the time during which they are heated, 
 dried, or soaked, and in the latter case on the nature of the 
 surrounding fluid. 
 
 There are first of all species which develope vigorously at a 
 temperature considerably above 50 C. Cohn and Miquel supply 
 instances of this, but the best is that of a Bacillus described by 
 van Tieghem (23), which grows and forms spores in a neutral nu- 
 trient solution at a temperature of 74C.; growth ceases at 77C. 
 
 The Bacilli obtained by Duclaux (24, 25) from cheese, and 
 named by him Tyrothrix, are instructive examples on all the 
 points above-mentioned. The vegetative cells of T. tenuis 
 cultivated in a neutral fluid were only killed at a temperature of 
 90-95 C., in a slightly alkaline fluid they bear a temperature 
 of over iooC., while the ripe spores remain capable of germin- 
 ation when subjected to a temperature of 115 C. in a similar 
 fluid. The most favourable temperature for vegetation in this 
 species is 25-35 C. T. filiformis in the vegetative state will 
 bear a temperature of iooC. in milk, but is killed in the space 
 of a minute in an acid fluid at the same temperature. The 
 spores of this species are uninjured at a temperature of i2oC. 
 in milk, but are killed at less than 110 C. in gelatine. Duclaux 
 gives similar accounts of other species. The vegetative cells also 
 of Bacillus Anthracis are said by Buchner (28, p. 229) to continue 
 capable of infection when heated for an hour and a half in 
 neutral and slightly acid fluids up to a temperature of 75-80 C. 
 Brefeld (19) found all the spores of Bacillus subtilis in a nutrient 
 solution kept for a quarter of an hour at a temperature of 
 
$ vi.] Conditions of vegetation. Moisture. 5 3 
 
 iooC. capable of germination; if they remained in it at the 
 same temperature for half an hour the majority still germinated, 
 if for one hour a smaller number; none retained their vital 
 power after a space of three hours. The spores were killed in 
 fifteen minutes at a temperature of 105 C., in ten minutes at 
 107 C., in five minutes at noC. 
 
 Fitz (21) found that the spores of his Bacillus butylicus 
 (B. Amylobacter) bear a temperature of 100 C.for a time vary- 
 ing from three to twenty minutes, according to the fluid in 
 which they happen to be. But if the time of exposure is pro- 
 longed, temperatures under iooC. are sufficient to kill them, 
 80 C. for example, when they are kept seven to eleven hours 
 in glycerine solution. 
 
 Spores, at least, are proof against still higher degrees of dry 
 heat ; those of Bacillus Anthracis, B. subtilis, and others con- 
 tinued capable of development in Koch's experiments (14, p. 305) 
 in a chamber heated up to 123 C. 
 
 Among the conditions connected with the nature of the en- 
 vironment, the requisite supply of water must be mentioned first 
 in this case as in that of all living cells. Withdrawal of water 
 to the point of air-dryness not only stops the process of vege- 
 tation but kills vegetative cells, at least in a number of cases, 
 in a very short time, those of Bacterium Termo, Cohn, and B. 
 Zopfii, for example, in seven days. But here, too, the effect 
 varies in different cases ; Micrococcus prodigiosus, for instance, 
 continues alive and capable of development for months in a 
 state of desiccation. 
 
 The resistance of spores to desiccation is greater than that of 
 vegetative cells. The spores of the arthrosporous Bacterium 
 Zopfii withstand it for seventeen to twenty-six days; those of 
 the endosporous Bacilli on the average certainly a year, those of 
 Bacillus subtilis, according to Brefeld, at least three years. 
 Here, too, limits and modifications will arise according to other 
 internal and external causes, but air-dry cells can hardly be 
 expected to retain their vitality for centuries. 
 
54 Lectures on Bacteria. [ vi. 
 
 Oxygen is not equally necessary in all cases. Two extreme 
 cases are distinguished in Pasteur's terminology as aerobia 
 and anaerobia. The first require an abundance of air con- 
 taining oxygen, as well as a good supply of nutrient sub- 
 stances for luxuriant vegetation and growth ; of this kind are 
 Micrococcus aceti, Bacillus subtilis, B. Anthracis, and Koch's 
 Spirillum of cholera. The other kind does well on good food 
 without oxygen ; free access of air reduces their vegetation to a 
 minimum or to zero, as for example in Bacillus Amylobacter. 
 
 Intermediate cases, however, are found between the two 
 extremes, as is well shown by Engelmann's beautiful example 
 which will be referred to again presently ; and according to the 
 investigations of Nencki, Nageli, and others, Bacteria which 
 excite fermentation, like the Sprouting Fungi which give rise to 
 alcoholic fermentation, grow luxuriantly without oxygen, when 
 they are in a suitable fluid capable of fermentation with them. 
 If these forms are placed in a less favourable nutrient fluid in 
 which they cannot incite fermentation, they will not grow with- 
 out a supply of oxygen. 
 
 Oxygen may impede and even destroy vegetation even in the 
 case of aerobiotic forms if it takes place under high pressure. 
 Bacillus Anthracis, for example, remained alive for fourteen days 
 in oxygen under a pressure of fifteen atmospheres, but was dead 
 in a few months' time. Duclaux contends that the germs even 
 of aerobiotic forms, when withdrawn from the conditions re- 
 quired for growth, lose their power of development more quickly 
 under the continued effect of atmospheric oxygen than when 
 oxygen is excluded. The facts on which this view is founded 
 are in themselves remarkable. In some glass bottles which had 
 been used in Pasteur's researches about 1860, and had been 
 kept hermetically sealed with their contents decomposed by 
 Bacteria, the germs of these Bacteria were found thoroughly 
 capable of development after twenty-one and twenty-two years. 
 Plugs of cotton-wool full of germs of all kinds, which had been 
 kept dry and protected from dust during the same time, but not 
 
$ vi.] Conditions of vegetation. Oxygen. 55 
 
 from contact with the air, did not contain a single living germ. A 
 few similar plugs which were only six years old contained germs 
 still capable of development. Duclaux' interpretation of these 
 facts may be correct, but it requires further proof, since we are 
 dealing with matters in which many other things besides the 
 supply of oxygen may have been unequal. Above all things it 
 is necessary in these questions that experiment should be made, 
 not with collective Bacteria, that is, with mixed masses which are 
 possibly or certainly undetermined, but always with a single 
 definite species. 
 
 Oxygen is taken up as material for respiration or breathing, 
 oxygen-breathing, to use a more precise term, carbon-dioxide 
 being at the same time given off. Water, except in some cases 
 which will be mentioned presently, serves as the agent and 
 medium of the chemical processes of the metabolism. Neither 
 of these bodies is properly a nutrient substance, that is, a sub- 
 stance from which carbon-compounds, the constructive material 
 for growth and cell-formation, are produced. 
 
 With respect to the true nutrient substances which therefore 
 supply building-material we must assume in the case of the few 
 green Bacteria, if they really contain chlorophyll, that accord- 
 ing to the analogy of all other plants containing chlorophyll, 
 they assimilate carbon as their food and give off oxygen. 
 Engelmann (26) has ascertained that a small portion of oxygen 
 is given off by his Bacterium chlorinum, and this supports the 
 assumption, while the employment of water also as a food- 
 material in the case of these forms, as in all other plants con- 
 taining chlorophyll, would also be probable. 
 
 The Bacteria containing no chlorophyll, which are by far the 
 greater number and almost the only ones which concern us 
 at present, require, like all cells and organisms that are devoid 
 of chlorophyll, carbon-compounds previously formed else- 
 where for the supply of their carbon, and do not assimilate 
 carbon-dioxide. The nitrogenous food-material may be furnished 
 both by previously formed organic and also by inorganic sub- 
 
56 Lectures on Bacteria. [ vi. 
 
 stances, compounds of nitric acid or still better of ammonia. 
 In addition to these a small supply quantitatively and quali- 
 tatively is required, as in other plants, of soluble constituents of 
 the ash. 
 
 It does not fall within the scope of these lectures to go more 
 deeply into the consideration of the value of the several com- 
 pounds as food-material; on this point the special literature, 
 especially Nageli's publications (27, 28), should be consulted. 
 It is sufficient for our general guidance and for practical pur- 
 poses to observe that according to Nageli's investigations a 
 number of moulds and Sprouting Fungi as well as Bacteria also 
 can find their food in solutions which contain nitrogenous and 
 non-nitrogenous nutrient substances in the following compounds 
 or combinations, the several solutions being arranged and 
 numbered in descending order according to their nutritiveness : 
 i. Proteid (peptone) and sugar. 2. Leucin and sugar. 3. 
 Ammonium tartrate or sal-ammoniac and sugar. 4. Proteid 
 (peptone). 5. Leucin. 6. Ammonium tartrate or ammonium 
 succinate, or asparagin. 7. Ammonium acetate. 
 
 But we must not seek to determine or judge of the optimum 
 of feeding - quality for all species or forms of Bacteria from 
 this table. The above scale is not even true for all moulds, 
 though it was first drawn up from the study of one of that group, 
 Penicillium glaucum. The requirements in the way of food of 
 single definite species of Bacterium have as yet been little studied, 
 and much needs more exact investigation. A number of prac- 
 tical experiences, which will be partly noticed further on under 
 the particular examples, point already to the great multiplicity 
 of the actual relationships which have to be taken into account. 
 
 Besides the amount of suitable food-material contained in the 
 substratum, other chemical qualities in it are also of importance 
 to the vegetative process in Bacteria. It is an old experience 
 that most of these organisms^ in contrast to the reverse be- 
 haviour of Sprouting Fungi and moulds, flourish best, other 
 conditions being the same, in a medium with a neutral or 
 
vi.] Conditions of vegetation. Food. 57 
 
 slightly alkaline or at most with a slightly acid reaction ; should 
 the reaction be strongly acid, vegetative processes are hindered 
 or wholly stopped. According to Brefeld (19) the development 
 of Bacillus subtilis, for example, is impeded, if 0-05 per cent, of 
 sulphuric or tartaric acid or 0*2 per cent, of lactic or butyric 
 acid is added to a good nutrient solution. But this, too, is 
 only a rule which has its exceptions ; the Bacterium of kefir 
 vegetates well, and, as far as our experience goes, best in milk 
 which has been rendered strongly acid by lactic and even acetic 
 acid ; the Micrococcus of vinegar vegetates in the same way in 
 an acid fluid. 
 
 Other soluble bodies also impede or destroy the vegetative 
 process when mixed with the food-material. This is of course 
 the case with substances which always act as poisons upon living 
 cells, such as corrosive sublimate, iodine, &c., when present in 
 sufficient quantity. But other bodies have a similar at least re- 
 tarding poisonous effect on Bacteria. Fitz, for instance, found 
 that the vegetation of his Bacillus of butyl-alcohol in a solution 
 of glycerine and under conditions otherwise most favourable was 
 impeded by the addition of 2-7-3-3 per cent, by weight of ethyl- 
 alcohol, o'9-i*o5 per cent, of butyl-alcohol, or o'i per cent, of 
 butyric acid. Since these prejudicial compounds are often 
 formed by the vegetative process itself, the latter may even be 
 stopped by the accumulation of its own products, as, for instance, 
 in lactic acid fermentation in sugars by the accumulation of 
 lactic acid ; if this is fixed, as by addition of chalk or zinc- 
 white, the vegetation of the Bacterium which causes the fer- 
 mentation continues. These phenomena are also found mutatis 
 mutandis, in other plants beside Bacteria, especially in Fungi, 
 and they vary in the individuals of different species. That 
 which disturbs one species may be of advantage to others, and 
 hence a change in the composition of the substratum may 
 favour the supplanting of one species by another, which was 
 previously perhaps present in the very smallest quantity. In 
 such a case the first species has prepared the ground for the 
 
58 Lectiires on Bacteria. [ vi. 
 
 others by its vegetative process and its products. This must 
 always be kept in mind in judging of processes on the large 
 scale ; attention to it supplies the explanation of a number of 
 phenomena which are at first sight puzzling. 
 
 The influence of other agencies besides those which have 
 been mentioned on the vegetation of Bacteria cannot in general 
 be disputed, but in the present state of our knowledge it is of so 
 subordinate importance, that a very short notice of it will be 
 sufficient on this occasion. The dependence of carbon-as- 
 similation upon the rays of light in the forms which contain 
 chlorophyll follows of necessity from what we know of the 
 function of chlorophyll. With respect to other effects of light 
 we have only some uncertain statements by Zopf on the pro- 
 bable promotion of the growth of Beggiatoa roseo-persicina by 
 illumination, and an investigation by Engelmann (29) into the 
 dependence on the rays of light of the movements of a form 
 which, though named Bacterium photometricum, is possibly, to 
 judge by the illustrations, not a Bacterium at all. Influence of 
 light has not been proved in the case of the majority of Bacteria. 
 The effects of electricity have been recently investigated by Cohn 
 and Mendelssohn (30), and may be gathered from their paper. 
 
 The dependence on the conditions of vegetation which we 
 have been considering is true of all stages and phases of the 
 normal vegetative process, not excepting its first beginnings, the 
 germination of the spores. Of this it must be specially remarked 
 that it occurs, as far as is at present known, only in a nutrient 
 substratum favourable to the vegetation of the species. This 
 agrees with the corresponding behaviour of some spores of Fungi, 
 those for example of Mucorini. It does not agree with that of 
 most other spores or with the seeds of flowering plants, which 
 germinate, or at least can germinate, without nutrient substances, 
 provided they are supplied with water, oxygen, and the necessary 
 warmth. 
 
 It has been already stated above on page 19, that in some 
 cases, as in Bacillus Amylobacter, spore -formaf ion takes place 
 
vi.] External conditions of vegetation. 59 
 
 even while vegetation and growth are going on in a portion of the 
 vegetative cells, and therefore while the conditions of vegetation 
 are still in operation. In other and especially in the endo- 
 sporous species it is true to say, that the formation of spores 
 begins when the substratum is exhausted, that is, has become 
 unsuitable for the vegetation of the species. Whether the latter 
 condition is really due in every case to a consumption of the 
 requisite nutrient substances or to an accumulation of checking 
 products of decomposition, or whether the formation of spores is 
 induced in this case as in others by internal causes when the 
 vegetation has reached a definite height, are all questions which 
 require more precise investigation, though they may perhaps be 
 of only subordinate practical importance. 
 
 Vegetation proceeds with great rapidity in most Bacteria 
 under the co-operation of the most favourable conditions. 
 Brefeld determined in the case of Bacillus subtilis, that with a 
 good supply of food and oxygen, and a temperature of 30 C., a 
 rod divides once in every thirty minutes, which means that it 
 doubles its length every thirty minutes, the thickness remaining 
 the same, and then separates transversely into two equal parts. 
 The process goes on more slowly in proportion as the condi- 
 tions recede from the optimum. If we assume that the increase 
 directly observed in the way here described is accompanied 
 by a corresponding increase in the mass, especially of the 
 dry substance, an assumption which is not strictly proved 
 but from the indications before us is certainly approximatively 
 correct, then we have growth to double the former size in the 
 full sense of the expression once in every thirty minutes. 
 Similar results are arrived at from observations on many other 
 species, as Bacillus Anthracis, B. Megaterium, &c. But here, 
 too, there are exceptions. The Bacterium of kefir, for example, 
 in the cases which I examined, required more than three weeks 
 for growing to about twice its weight, more than 500 times the 
 period observed in Bacillus subtilis. I am not able to say 
 whether the conditions were absolutely the most favourable ; at 
 
60 Lectures on Bacteria. [ vi. 
 
 all events, they were those in which the kefir-organism grows best 
 according to our present knowledge, namely, in milk at an air- 
 temperature of 1 5-20 C., and with a supply of atmospheric air. 
 
 The movements also of the Bacteria, as well as their growth 
 and germination, are directly dependent on the conditions of 
 vegetation in the species and forms which are capable of inde- 
 pendent movement. The occurrence and the direction of the 
 motion are specially determined by the influence of nutrient 
 substances, and of oxygen. If a form of this kind, Bacillus 
 subtilis for instance, in the vegetative condition in which it is 
 capable of movement is placed in a drop of nutrient solution on 
 a slide under a cover-glass, the motile rods are seen to collect 
 at once round the margin of the cover-glass where the oxygen 
 of the air has free access. The comparatively few which remain 
 behind in the centre of the drop, and are there cut off from the 
 atmospheric oxygen, become slower in their movements and 
 finally lose them altogether. Aerobiotic forms enclosed in a 
 drop of water in which there is no free oxygen along with 
 Algae containing chlorophyll at first remain motionless. But 
 as soon as the cells containing chlorophyll are induced to give 
 off oxygen under the influence of light, the Bacteria begin to 
 move actively, as Engelmann (31) has shown, and the movement 
 is directed towards the spots where the oxygen is being given 
 off. Here the Bacteria collect, and they may therefore be used 
 as an extremely delicate reagent for the detection of quantities 
 of oxygen of almost inconceivable minuteness. The frequent 
 grouping of aerobiotic forms into films or membranes on the 
 surface of fluids is no doubt partly due to the influence in 
 question determining the direction of the movement. 
 
 While the above-mentioned forms approach as near as pos- 
 sible to the source of the atmospheric oxygen, there are others 
 which, as Engelmann (26) found in the case of a Spirillum, 
 always remain at a certain distance from it, the distance 
 diminishing as the amount of free oxygen diminishes in the air 
 which finds access to the Bacteria. This observation proves the 
 
$ vi.] Culture of Bacteria. 61 
 
 existence of intermediate cases, mentioned above, between ex- 
 treme aerobia and anaerobia. 
 
 Pfeffer (32) has further shown that chemical stimuli, exerted 
 by other bodies in a state of solution, may influence cells which 
 have the power of locomotion and organisms of very various 
 kinds, hastening and determining the direction of their move- 
 ment, and that the Bacteria supply special instances of this 
 general phenomenon. The chemical bodies which have this 
 effect on the Bacteria are those which were spoken of before as 
 their nutrient substances. The direction of the movement is 
 due, as Pfeffer shows, to diffusion-currents by the introduction of 
 the solutions on one side, the axis of rotation of the cells being in 
 the same direction as the currents and the movement in space 
 in the opposite direction. Other conditions remaining the same 
 the effect varies according to the quality of the body in solution 
 and the concentration of the solution, and it must be particularly 
 observed that it is not every diffusion-current that influences the 
 direction of movement, but only the current from solutions 
 determined in each case by the species of Bacterium. These 
 facts explain a phenomenon which has been frequently observed, 
 namely, that swarms of Bacteria assemble in water round solid 
 bodies, such as dead parts of plants, pieces of flesh and the like, 
 which gradually give off soluble nutrient substances. 
 
 The practical application of these remarks on the conditions 
 and phenomena of vegetation in conjunction with the ascertained 
 facts respecting germs and their dissemination are in the main 
 obvious, if the important points and conditions in each case are 
 kept clearly in mind. We require always a certain amount of 
 positive knowledge and careful consideration of the object which 
 we desire to attain and can really attain in a particular way. The 
 practical remarks therefore may, for the present, be summed up 
 in a very few words. 
 
 First, with respect to the culture of Bacteria, there is but 
 little to be said. Pure extracts of animal and plant-substances, 
 the meat-extracts sold in the shops, broths, the juice of 
 
62 Lectures on Bacteria. [ vi. 
 
 fruits, neutralised, if necessary, and dissolved in not too con- 
 centrated (about 10 per cent.) watery solutions or in gelatine, 
 are, as a rule and in accordance with general experience, good 
 nutrient substrata ; the special choice must be made by experi- 
 ment in each case. Fresh urine has been repeatedly used with 
 success by French observers. The serum of blood has been 
 found to be a very suitable substance, and is almost the only 
 one that can be used in the cultivation of some parasitic forms, 
 especially if made stiff by being heated up to 60-70 C. after the 
 mode of proceeding described by Koch. 
 
 Among the very first requisites are the securing the purity of 
 the species under cultivation, the absence of unintentional ad- 
 mixtures, on which point some practical hints were given in a 
 former lecture (pp. 34 and 41), and the perfect control of the 
 continued purity of the cultures. The possibility of different 
 species displacing each other has been already discussed (p. 32). 
 
 To obtain purity of a culture as well as for other practical 
 purposes, it is often necessary to effect the entire destruction or 
 death of germs present in it. In the conduct of cultures there 
 is the special risk of these germs adhering to the apparatus to 
 be employed, vessels, nutrient substances, &c., and they must 
 be killed in order to provide for the purity of the culture. This 
 process of destruction is known as sterilisation, an expression 
 introduced by the school of Pasteur. 
 
 Bodies poisonous to protoplasm, such as acids, corrosive sub- 
 limate, &c., if sufficiently concentrated will usually effect the de- 
 sired result, where the object is only to destroy, of course on the 
 one condition that they are able to force their way into the proto- 
 plasm which is to be killed. This is the case in most poisons 
 but not in all. Absolute alcohol is a poison which is imme- 
 diately fatal to protoplasm, and it must therefore kill the proto- 
 plasm of endosporous Bacilli, if it reaches them. Nevertheless, 
 the spores of Bacillus Anthracis, as Pasteur discovered, and no 
 doubt also those of other endosporous species retain their vitality 
 after lying several weeks in absolute alcohol. If the same ex- 
 
J vi.] Culture of Bacteria. Sterilisation. 63 
 
 periment is made with sound ripe seeds of the ordinary garden 
 cress, Lepidium sativum, the same result is obtained ; they ger- 
 minate if they are taken from the alcohol after four weeks' time, 
 and washed and sown. The spores of the Bacillus and the 
 seeds of the cress agree in being enveloped all round in a gela- 
 tinous membrane into which the alcohol cannot penetrate, and 
 thus the protoplasm, which in the cress-germ would otherwise 
 be certainly killed at once, remains unattacked. 
 
 But the application of poisons to cultures for purposes of 
 sterilisation is attended with great inconveniences in all the many 
 cases in which they must be got rid of again that they may do no 
 injury to the culture itself. New impurities may be introduced in 
 the process of washing the vessels and the rest of the apparatus. 
 
 Hence much the most practical mode of sterilisation consists 
 in. the application of extremely high temperatures, which must 
 exceed iooC., if the object is to kill any spores that may pos- 
 sibly be present; in dry vessels it is best to raise it to 120- 
 150 C. In the sterilising of fluids a heat of even 100 C. may not 
 always be possible for practical reasons, as, for example, when it 
 is necessary to avoid the coagulation of the albuminous sub- 
 stances dissolved in the fluid. Since most vegetating cells are 
 killed by a temperature of 50-60 C., the plan suggested by 
 Tyndall (33) is the most effective ; the fluid is allowed to stand 
 till whatever germs it contains begin to grow; if it is then 
 heated to 60-70 C. and the process repeated at an interval of 
 two days, the fluid will be in most cases free from Bacteria, 
 always presupposing of course that the plug which closes the 
 vessel is compact and clean. 
 
 Lastly, in practical life all that is usually required is to 
 render harmless any germs that may be present by preventing 
 their further development, whether they continue capable of it 
 or not. Here, too, complete destruction would be best and 
 most desirable ; but the use of most poisons in the state of con- 
 centration which is most certainly fatal, or that of a certainly 
 fatal degree of heat, would also ordinarily lead to the destruc- 
 
64 Lectures on Bacteria. [jj vii. 
 
 tion of the objects intended to be protected from the Bacteria. 
 We must therefore be content with what is within our reach. 
 
 If, as there is no reason to doubt, the favourable results of the 
 application of disinfectants at the present day, the splendid 
 results of antisepsis in surgery, are due to the protection obtained 
 against destructive Bacteria, there can be at the same time little 
 doubt that this protection, partly due to the absence of germs 
 through the increase of cleanliness consequent on these modes 
 of procedure, is chiefly secured by staying the development of 
 the germs and in a much less degree by their destruction. The 
 elaborate experiments of Koch (14, p. 234) show that of the 
 various disinfecting and antiseptic agents in the proper state of 
 concentration or dilution, only corrosive sublimate, chlorine and 
 bromine have the effect of killing the germs. Bodies like 
 salicylic, carbolic, and other acids in the suitable state of 
 dilution, and powdered cane-sugar can only be supposed to have 
 the desired effect by stopping the growth of the Bacteria. It 
 wou^d be highly important to enquire more closely into the 
 specific sensibilities which may exist in the different species of 
 Bacteria. The behaviour of a Micrococcus of ulcer or erysipelas 
 in the presence of antiseptics may possibly be different from that 
 of Bacillus Anthracis, which has been the chief subject of Koch's 
 study. 
 
 VII. 
 
 Relation to and effect upon the substratum. Sapro- 
 phytes and Parasites. Saprophytes as exciting 
 decompositions and fermentations. Characteristic 
 qualities of Forms exciting fermentation. 
 
 THE vegetative process in organisms, which use organic com- 
 pounds for their food, must necessarily effect changes in the 
 substratum from which this food is withdrawn. To these 
 changes are added other effects, more closely connected with 
 the process of respiration, which lead to profound transforma- 
 tions in the organic substratum. 
 
vii.] Relation to the substratum. Saprophytes. 65 
 
 This is especially the case with organisms whose mode of life 
 is of the kind described and therefore with all that do not 
 contain chlorophyll, Infusoria and Fungi as well as Bacteria. 
 Fungi, especially in the narrower use of the word, Sprouting 
 Fungi, moulds, &c. being comparatively easy to examine, have 
 supplied the best and most numerous conclusions with respect 
 to the phenomena in question, and we shall often have to make 
 use of them as examples in the following remarks. 
 
 The interest attaching to the Bacteria which are devoid of 
 chlorophyll rests chiefly on their effects on their substratum, and 
 after the foregoing introduction we must proceed to consider 
 these organisms, and endeavour to give a clear idea of them 
 by calling attention to the most important known examples. 
 
 Organisms not containing chlorophyll are separated into two 
 primary divisions, according as the organic substratum is a 
 living or a dead body. Those which have their habitat on or 
 in living fellow-creatures, and derive their sustenance from them 
 are termed parasites ; the others which live on dead bodies are 
 known as saprophytes. Different species are in fact differently 
 adapted to one or the other mode of vegetation; some are 
 known both as parasites and saprophytes, others only in one 
 or the other character. 
 
 We shall subsequently have to go more deeply into these 
 distinctions and gradations, especially in the case of parasites. 
 This brief mention of them is sufficient for the present. 
 
 The particular account of these forms will be simpler and 
 more intelligible if it begins with saprophytes. The organic 
 compounds present in bodies inhabited by saprophytes are split 
 up into simpler substances; in extreme cases total oxidation, 
 rotting, takes place with the decomposition of non-nitro- 
 genous carbon-compounds into the final products of carbon 
 dioxide and water ; in other cases we have partial oxidations, 
 not proceeding so far as the final products of combustion, 
 ' oxidation-fermentations,' as for example in acetous fermenta- 
 tion that is, the formation of acetic acid by the oxidation of 
 
 F 
 
66 Lectures on Bacteria. [ vn. 
 
 ethyl-alcohol. Reductions are of rarer occurrence, as in the 
 splitting of sulphates by Beggiatoa, which will be described 
 presently. The last to be mentioned are the splittings which 
 end in other than simple products of oxidation and are included 
 under the general term of fermentations ; of these the best- 
 known example in every respect is the alcoholic fermentation, 
 which is the splitting of the different sugars into ethyl-alcohol 
 and carbonic acid. If these splittings are accompanied with a 
 development of offensive gas, especially in compounds containing 
 nitrogen, the term putrefaction is used, an expression rather 
 popular and expressive than strictly and scientifically defined. 
 
 It is no part of our subject to enter further into the chemical 
 nature of these processes, the purely chemical and physical 
 sides of the theories of fermentation. With regard to the 
 general history of these theories also, we shall only observe 
 that it has been an established scientific truth since about the 
 year 1860, that the entire series of phenomena of rotting 
 and fermentation above mentioned are the results of processes 
 of life and vegetation in certain lower organisms, especially 
 Fungi and Bacteria. To Pasteur belongs the entire credit of 
 having placed this vitalistic theory of fermentation on a firm 
 basis, in opposition to other views which acknowledged no 
 causal relations at all between it and living organisms or causal 
 relations of a different kind, and of having extended it to all 
 phenomena of a similar kind. It is true that the same 
 vitalistic theory has been distinctly expressed in the case of 
 alcoholic fermentation since the time of Cagniard-Latour (1828) 
 and Schwann (1837), but it never obtained general accep- 
 tation. 
 
 The vegetative process of living organisms is then the direct 
 cause of fermentations ; there is no fermentation if the organisms 
 are destroyed. Organisms of this kind are therefore termed 
 fermentation-exciters, ferment-organisms, or simply ferments 
 in the terminology of the school of Pasteur. In that of Nageli 
 they are known as yeast, and according as the ferment-organism 
 
viz.] Relation to the substratum. Fermentation. 67 
 
 is a Sprouting Fungus, a Fission-fungus, that is a Bacterium, or 
 a Filamentous Fungus, it is shortly termed Sprouting Yeast, 
 Fission Yeast, or Filamentous Yeast. The French system of 
 terminology limits the application of the French word levure, 
 which had originally the same meaning as the German Hefe and 
 English yeast, to the Sprouting Fungi which excite fermentation. 
 It is essential to the understanding of the literature to observe 
 that the German Hefe, English yeast, is used in quite different 
 senses ; it must be added also, that the same word is applied not 
 only to the ferment- organism simply, or to the particular form 
 of Sprouting Fungus which excites fermentation, but also to all 
 forms of Sprouting Fungi whether they excite fermentation or 
 not, thus often causing very needless confusion. 
 
 We shall speak again presently of the different meanings of 
 the word ferment. 
 
 Since the vegetation of organisms sets up fermentation, the 
 substratum in which the fermentation is to take place must 
 contain all the nutrient substances necessary for the process of 
 vegetation. A pure saccharine solution, for example, does not 
 ferment if a small quantity of fermentation-exciting Fungi or 
 Bacteria also in a pure state is introduced into it. The sugar, as 
 we have seen, is a good nutrient material for these organisms. 
 But it only supplies the necessary amount of carbon, the elements 
 of water, and free oxygen, and is therefore imperfect as food. It 
 is only when the compounds which supply the nitrogen men- 
 tioned above and the ash-constituents are added to the solution 
 that it is rendered capable of fermentation, and fermentation 
 commences as soon as the conditions favourable to vegetation 
 are secured. Bodies which in the natural course of things or 
 when artificially prepared have finished fermenting, such as 
 must or brewers' mash, are proper food for ferment- 
 organisms. 
 
 In every process of fermentation there is first of all a growth, 
 a multiplication of the exciting organism at the expense of the 
 fermenting substance. This can be seen by direct observation 
 
 F 2 
 
68 Lectures on Bacteria. [$ vn. 
 
 when the smallest possible quantity of the organism is intro- 
 duced in the beginning, and its weight exactly determined. 
 The rest of the substratum is split up into the products of 
 fermentation in consequence of the processes of decomposition 
 which are connected with the vegetation, and which, as has 
 been already said, cannot be further considered here. The 
 best-known example of the kind is the alcoholic fermentation 
 of sugar by the Sprouting Fungus of beer-yeast, Saccharomyces 
 Cerevisiae, though it certainly does not strictly belong to the 
 subject-matter of these lectures. Pasteur states that in a suitable 
 solution about 1*25 per cent, of sugar was used for the formation 
 of yeast-substance, 4-5 for that of succinic acid and glycerine, 
 the remainder, 94-95 per cent., was broken up into alcohol and 
 carbonic acid. 
 
 This example shows that the process of decomposition is 
 complex, and does not simply consist in the breaking up of all 
 the sugar into carbonic acid and alcohol. But these, in point 
 of quantity and from their importance to human requirements, 
 are the most prominent products of the fermentation in ques- 
 tion. Accordingly, we distinguish in this and all other cases 
 primary and secondary products of fermentations, and we name 
 the particular process of fermentation from some characteristic 
 primary product. 
 
 It is known that the nature of the fermentations set up by 
 Bacteria is in general analogous with that of the case just men- 
 tioned. But in most of them the splitting-process is at present 
 less exactly understood, and in many only the primary products 
 are qualitatively known. Among these carbonic acid constantly 
 makes its appearance, as in Saccharomyces. Further remarks 
 will appear below along with special examples. At present we 
 will only briefly call attention to the colouring matters which 
 are observed not unfrequently in fermentations with Bacteria ; 
 they were noticed before on page 4, and have given rise to the 
 expression pigment-fermentations. 
 
 Some, but not all, ferment-organisms give off into the fluid 
 
$ vii.] Relation to the substratum* Enzymes. 69 
 
 medium dissolved substances, which in the very minute quantity 
 in which they are excreted are able to give rise to other changes 
 in the substratum than those which belong directly to the 
 process of fermentation. Analogous products with analogous 
 effects are often obtained from other sources also, for instance 
 in Fungi which do not excite fermentation, and on certain 
 organs or in the cells of higher organisms, even of plants 
 containing chlorophyll. The Fungus of beer-yeast, for example, 
 Saccharomyces Cerevisiae, excretes a substance which inverts 
 cane-sugar in solution, as the phrase is, that is by absorbing 
 water splits it into glucose and laevulose (grape-sugar and fruit- 
 sugar). By means of a similar excretion Bacillus Amylobacter 
 breaks up cellulose into products soluble in water. The 
 cells of germinating seeds produce a body, diastase, which 
 breaks up starch-granules into dextrin and maltose. Substances 
 of this kind are known as enzymes or unformed or unorganised 
 ferments, in German terminology simply ferments. The ter- 
 minology of the French schools consistently carried out, especially 
 by Duclaux, terms them generally diastases, and then for the 
 separate cases invents special words, all having the same ending, 
 as amylase, saccharase (' sucrase'!), casease, and so on, reserving 
 the word ferment, as we have learned, for the living ferment- 
 organisms themselves. Enzymes, as has been already intimated, 
 are either unorganised bodies or bodies with a definite form, 
 soluble in water, and are all allied as regards chemical character 
 to the proteid compounds. They can with proper manage- 
 ment be separated from the organisms which produce them 
 without putting an end to their activity. Their characteristic 
 mark as a rule is the power which they possess of causing 
 chemical changes, chemical separations, without passing them- 
 selves into the final products of these changes and so losing 
 their active powers. Their effects are specifically different in 
 every case, and they are accordingly distinguished, as in the 
 examples cited, into inverting, sugar-forming, and other enzymes, 
 to which may be added those that, like the pepsin of the gastric 
 
70 Lectures on Bacteria. [ vn. 
 
 juice of animals, convert albuminous bodies with absorption 
 of water into easily soluble peptones, peptonising enzymes. 
 
 After what has now been said it scarcely requires to be 
 pointed out that every organism which sets up fermentation or de- 
 composition displays a specific activity in the directions indicated, 
 and it may be also a specific formation of enzymes. In the 
 same saccharine solution one species excites alcoholic fer- 
 mentation, another lactic acid or butyric acid fermentation, and 
 so on. Again, the same fermentation, according to the primary 
 products, may also be produced by dissimilar species under 
 otherwise similar conditions, though in unequal quantitative 
 amount. Alcoholic fermentation, for example, is excited in 
 saccharine solutions by several species of Saccharomyces, and 
 also by certain species of the group of Mucorini. The same 
 species can also set up different decompositions in different sub- 
 strata. The vinegar-bacterium oxidises the alcohol in a dilute 
 solution, and converts it into acetic acid and this into carbonic 
 acid and water when the alcohol is exhausted. The Saccharo- 
 myces of beer-yeast changes grape-sugar by fermentation 
 directly into carbonic acid and alcohol ; cane-sugar does not 
 ferment, but is first ' inverted ' by the above-mentioned enzyme, 
 and the ' invert-sugar ' formed of glucose and laevulose ferments 
 as it arises. 
 
 The Bacillus of butyl-alcohol of Fitz (Bacillus Amylobacter, 
 see Lecture IX) vegetates in nutrient solutions of milk-sugar, 
 erythrite, ammonium tartrate, salts of lactic acid, malic acid, 
 tartaric acid, &c., without exciting characteristic fermentations 
 in them ; it produces fermentation in glycerine, mannite, and 
 cane-sugar, with carbonic acid, butyric acid, and butyl-alcohol 
 as the primary products, and small amounts of lactic and other 
 acids as secondary products, the quantities of the primary pro- 
 ducts varying much according to the nature of the substratum. 
 The relative quantities of butyric acid, for example, under similar 
 conditions of fermentation, are 17-4 in the case of glycerine, 
 35-4 in that of mannit'e, and 42-5 in that of cane-sugar. 
 
viz.] Relation to the substratum. Enzymes. 71 
 
 Many similar examples are to be found in works on fermen- 
 tation. 
 
 The production of enzymes may also vary in the same form 
 according to the quality of the substratum. Wortmann (34) found 
 in the case of a Bacterium which he does not further determine, 
 that it excretes a starch-dissolving enzyme, and dissolves starch 
 if carbon is presented to it in the form of starch-grains only. 
 If the carbon is offered it in the form of a carbohydrate 
 which is readily soluble in water, such as sugar, or of tartaric 
 acid, the starch-grains which are offered to it at the same time 
 remain untouched. Similar facts are recorded of Bacillus 
 Amylobacter, which, according to van Tieghem, when fed with 
 glucose, leaves the cellulose which is presented to it at the same 
 time untouched, but decomposes it and takes it in as food if no 
 source of more readily assimilable carbon is available. 
 
 Lastly, the definite activity of a particular species in the way 
 of fermentation or decomposition may be reduced to zero by a 
 change in the external conditions within the limits of vegetation, 
 even when the quality of the nutrient material remains the same. 
 Examples of this are furnished by the Mucorini already men- 
 tioned in passing, by the different species of Saccharomyces, 
 and by Bacillus Amylobacter and other Bacteria. Bacillus 
 Amylobacter, according to Fitz, loses the power of causing fer- 
 mentation, without losing that of vegetation, when exposed to a 
 high temperature, for instance, after the spores are boiled from 
 1-3 minutes in a solution of grape-sugar, or after being heated 
 for 7 hours up to 80 C. ; the same effect is produced if it is 
 cultivated during many generations with a copious supply of 
 oxygen in a nutrient solution, in which it is unable to excite 
 fermentation. The Mucorini present themselves in very dif- 
 ferent forms according to the change of conditions, though the 
 form is quite fixed in each particular case. Such a change of 
 form does not occur in Saccharomyces and the Bacteria which 
 have been more thoroughly examined as to this point, or only 
 to an inconsiderable degree. That external conditions of every 
 
72 Lectures on Bacteria. [ vm. 
 
 kind should have some influence on the form of Bacteria is a 
 legitimate a priori assumption, and may be directly observed 
 from the facts stated on page 29. It is therefore highly 
 probable, though further distinct proof is required, that the 
 change of form of strongly pleomorphous Bacteria (see pp. 25-6) 
 is to a large extent determined by changes in the external 
 conditions of vegetation. 
 
 In the natural course of things the processes of development 
 and decomposition of which we have been speaking, seldom if 
 ever go on their way purely and smoothly from beginning to 
 end. Many of the organisms in question are so numerous that 
 their germs find their way simultaneously or in rapid succession 
 into a nutrient solution or other decomposable substratum. In 
 that case they either develope simultaneously and the effects of 
 their decomposing action appear side by side ; or some find a 
 favourable substratum at first, but changing its character by their 
 vegetation, which is thereby impeded, they thus prepare a highly 
 favourable substratum for other forms ; in this way various de- 
 velopments and decompositions make their appearance, one 
 after another, in the same substratum. 
 
 Examples of such combinations and successions of products 
 of fermentation and decomposition are found everywhere in the 
 natural course of things, and in matters connected with domestic 
 economy. There is less need for me to dwell on them here, 
 because many of them will have to be noticed in the succeeding 
 descriptions of the several species. 
 
 VIII. 
 
 Most important examples of Saprophytes. The nomen- 
 clature explained. Aquatic Saprophytes : Crenothrix, 
 Cladothrix, Beggiatoa; other aquatic forms. 
 
 IN proceeding now to the special consideration of a few 
 saprophytic Bacteria, three remarks must first be made. First, 
 
.] Examples of 'Saprophytes. Nomenclature. 73 
 
 we cannot attempt to give an account of all the phenomena 
 which have been described. We confine ourselves to such as 
 are at present best known, and are at the same time of more 
 general interest. It is to be presumed that many more will 
 have to be added to these in the course of time, and that various 
 changes will have to be made in the views at present enter- 
 tained. We are still very much in the position of beginners as 
 regards our knowledge of these matters and our investigations. 
 Secondly, we do not propose to go any further into the details 
 of the chemical processes attending the work of decomposition ; 
 we are chiefly concerned with the morphological and biological 
 points of view. Thirdly, we must keep clearly in mind that our 
 knowledge of the morphology and biology of the Bacteria is at 
 present very imperfect, or at least very unequally developed. 
 So much is this the case, that we are not yet in a position to 
 attempt a consistent classification and nomenclature on the 
 principles of systematic botany. What at present seems like 
 such a classification is only a temporary expedient. In such a 
 case the only thing to be done is to agree upon a provisional 
 arrangement and nomenclature for the time being. We will 
 therefore, first of all, adhere to the primary division into endo- 
 sporous and non-endosporous or arthrosporous forms proposed 
 in Lecture III. Single better-known groups in these two 
 divisions may and must then be constituted genera, and receive 
 names capable of being precisely defined. We limit the use of 
 the name Bacillus, and apply it to all endosporous forms and 
 species with rod-like vegetative cells and cell-unions of the 
 first order. Single arthrosporous forms, such as Beggiatoa, 
 Cladothrix, Leuconostoc, Sarcina and others, may be separated 
 from the rest and distinguished by characters which will be de- 
 scribed presently. There still remain a number of forms, in 
 respect of which we are reduced to superficial distinctions of 
 shape, and their ultimate classification must therefore be deferred. 
 Among these the spiral forms may be included under the name 
 Spirillum. Some of these, according to van Tieghem, belong 
 
74 
 
 Lectures on Bacteria. 
 
 vm - 
 
 to the endosporous division ; others appear to be arthrosporous, 
 while there is a third group in which the point is not yet ascer- 
 tained, but appearances are in favour of their being kept together, 
 
 as at present, under the same 
 genus. The rod-forms which 
 are not known to be endo- 
 sporous may all be termed 
 Bacterium, and the coccus- 
 forms (page 9) Micrococcus. 
 It is obvious that no sharp 
 line of distinction can be 
 drawn between Micrococci 
 and short rod-shaped Bac- 
 teria, but it is convenient 
 and customary to distinguish 
 them. The species too, which 
 are at present distinguished, 
 require care in their deter- 
 mination. Some of them are 
 certainly known to be fully 
 and clearly distinct ; of others 
 this cannot be said, and 
 their present names in all 
 probability include two or 
 more species which have 
 yet to be studied severally. 
 Thus it seems to me quite 
 certain that more than one distinct species has been described 
 
 Fig. 5. Crenothrix Kiihniana, Rabenhorst. n group of young filaments 
 attached below, a, b older filaments ; at the upper end of b single cells are 
 issuing from the opened sheath, c broad filament with flatly disk-shaped 
 cells in its upper portion, which are divided in basipetal succession along 
 the length of the filament into minute round spore-cells ; the spores are 
 issuing from the uppermost extremity of the open sheath, d, c spores 
 developing into young filaments. After Zopf. n magn. 450, a, b 540, 
 d, e 600 times. 
 
$ viii.] Aquatic Saprophytes. Crenothrix. 75 
 
 under the name of Bacillus subtilis. Such collective names col- 
 lective species, as we may shortly say have occurred in all 
 branches of natural history and have been gradually dis- 
 entangled ; here, too, they will ultimately be cleared up. We 
 have only to keep an eye upon them, and not be induced by 
 names to adopt premature conclusions respecting them (35). 
 
 We will now proceed to give some examples. 
 
 The comparatively large arthrosporous forms, which are 
 described under the names of Crenothrix, Cladothrix, and 
 Beggiatoa, are found often in injurious, or at least in very dis- 
 agreeable quantities, in waters containing organic substances in 
 solution (36). 
 
 i. Crenothrix Kiihniana, Rabenhorst (Fig. 5), in the most highly 
 differentiated stage of its development, forms filaments, accord- 
 ing to Zopf, 1-6 p. thick and about i cm. long, attached at one 
 end to fixed bodies, entirely unbranched, straight or less often 
 slightly spirally twisted. The filament consists of a row of 
 cylindrical cells, which are half to about one and a half 
 times as long as broad. The outer layers of their lateral 
 walls coalesce and form a delicate sheath surrounding the whole 
 filament, which is colourless when young, but at a later period 
 is often coloured from yellowish to dark brown or brownish 
 green by salts of iron. The filaments not unfrequently break up 
 transversely into pieces, which float free in the water and collect 
 into flocculent masses. The segments of the filaments may pass 
 by repeated bipartitions into the form of isodiametric cells which 
 then round themselves off. In this way the cells of thicker 
 filaments first take the shape of flattish disks, and then divide 
 one or more times in the longitudinal direction of the filament 
 into small roundish cells (b, c}. These ultimately escape from 
 the sheath, either because the sheath swells up along its whole 
 length, or because it swells up and opens at the apex only and 
 allows the small cells to escape at that point ; the cells are either 
 passive and are thrust forth by the continued growth in length 
 of the lower portions of the filament, or have a slow movement 
 
76 Lectures on Bacteria. [ vm. 
 
 of their own. These minute cells may be called Cocci from their 
 form, or spores on account of their capability of further de- 
 velopment, for when cultivated in bog-water they develope into 
 new filaments resembling the parent-filaments (d, e). ' On the 
 other hand they may retain the Coccus-form and multiply, pro- 
 ducing at the same time a large quantity of jelly, and in this 
 state they form Zoogloeae, which vary in size from microscopical 
 minuteness to more than i cm. in diameter. They also occa- 
 sionally pass, according to Zopf, into the motile condition, and 
 back again into the resting-state. The Zoogloeae are at first 
 without colour, but like the sheaths of the filaments they gradu- 
 ally become coloured by deposition of iron. The Cocci also 
 may ultimately develope from the Zoogloea-state into the fila- 
 ments as at first described. The external conditions for these 
 formations are not certainly understood. 
 
 Crenothrix Kiihniana is found in every kind of water, even in 
 the water of the soil as far as twenty metres below the surface. 
 It may become a formidable nuisance in water-pipes, drain- 
 pipes, and the like, in which its tufts of filaments and its Zoo- 
 gloeae increase to such an extent as to form dense gelatinous 
 masses stopping up the passages; in reservoirs it may form 
 slimy layers several feet in depth. The water is thus ren- 
 dered unfit for drinking and for various technical uses, though 
 no direct injury to human health has been traced to the Creno- 
 thrix. We do not know that any other processes of decom- 
 position are caused by Crenothrix. 
 
 2. Cladothrix dichotoma, Cohn is of still more frequent occur- 
 rence than Crenothrix, especially in dirty water, such as the 
 outflow from manufactories and from similar sources, and also 
 in streams (Fig. 6). It often forms extensive films of flocculent 
 matter of a grayish white colour floating near the edge of the 
 water. Its delicate filaments, ensheathed as in the preceding 
 species, are chiefly distinguished from those of Crenothrix in 
 the full-grown state by being branched. Branching is effected 
 by any single cell of a filament bending one of its extremities 
 
viii.] Aquatic Saprophytes. Cladothrix. 77 
 
 laterally out of the line of the rest, and then growing on in the di- 
 vergent direction and dividing transversely. 
 The divergent branch forms an acute angle 
 with the primary filament, and in relation 
 to the point of attachment or base of the 
 latter the angle is usually open upwards, 
 seldom the reverse. This form of branch- 
 ing, which is of common occurrence in the 
 Nostocaceae, in Scytonema, for example, 
 and Calothrix, has been termed false 
 branching, because the part which the 
 individual cells take in it, morphologically 
 speaking, is not the same as in most 
 of the other lower plants which have 
 filaments formed of a single row of cells ; 
 it is false only in this sense, and is really 
 a peculiar mode of branching. 
 
 Whatever else is known of the structure 
 and development of Cladothrix, especially 
 since Zopfs researches, so far agrees 
 with the accounts given of Crenothrix, 
 that only a few remarkable particulars 
 need be touched upon here; Zopfs 
 monograph should be consulted. First 
 of all it is not perhaps superfluous to re- 
 mark that Cladothrix also receives a de- 
 
 Fig. 6. 
 
 posit of iron oxide in the sheaths of its filaments, and becomes 
 
 Fig. 6. Cladothrix dichotoma, Cohn. a extremity of a live filament, which 
 grew originally in the direction r p. The branches n, n have been formed 
 by lateral divergence and subsequent growth of segment-cells in the new 
 direction. The construction of the filament out of cylindrical segment-cells 
 is clearly shown at the apex of the branches ; elsewhere it is recognisable 
 only by the aid of reagents, b portion of a filament showing the segmen- 
 tation and the sheath ; the latter is empty in its upper half, except 
 where one cylindrical cell remains fixed in it. Magn. 600 times, but made 
 a little too broad in the drawing. 
 
78 Lee hires on Bacteria. [$ vm. 
 
 coloured accordingly. The often striking accumulations 
 of ochre-coloured slime-masses in springs and small streams 
 which contain iron, the filamentous constituents of which are 
 known by the old name of Leptothrix ochracea, Kiitzing, 
 consist, according to Zopf, of this iron-containing Cladothrix. 
 
 The filaments multiply by the abscision and further growth 
 of portions, which form longer or shorter rods according to 
 their size a mode also very common among the allied Nos- 
 tocaceae and also, according to Zopf, by means of spores or 
 ' Cocci/ that is, short rounded cells, which issue from the sheath 
 and develope into filaments. 
 
 The filaments, or single branches of them, instead of retaining 
 the usual tolerably straight form, may become spiral with more 
 or less narrow or open coils, and these spiral forms also may 
 break up transversely into separate pieces. 
 
 Both the longer and the shorter abscised rod-shaped and 
 spiral portions of filaments, and the round spores and Cocci 
 also, not unfrequently become motile, the longer ones 
 creeping or gliding with a slow movement, the short forms 
 displaying an active swarming motion, such as is described on 
 page 7. 
 
 Lastly, the four forms, the filamentous, the rod-like, the spiral, 
 and the coccoid, whether mixed together or separate from one 
 another, may remain united by a jelly into Zoogloeae, which 
 sometimes appear as bodies of considerable size with shrub- 
 like branching. The short forms may again become motile, 
 and swarm out of a Zoogloea; but they may also develope 
 again into the filamentous form, the typical form from which we 
 set out ; this has certainly not been directly observed in the case 
 of the spiral rods. 
 
 If all these statements are correct, Cladothrix supplies the 
 most complete example of a pleomorphous course of develop- 
 ment. 
 
 No more is known of injurious properties and decomposing 
 power in Cladothrix than in Crenothrix. 
 
$ viii.] Aquatic Saprophytes. Beggiatoa. 79 
 
 3. The species of Beggiatoa (Fig. 7) agree closely, according 
 to Zopf, with Crenothrix and Cladothrix in their pleomorphous 
 course of development. Straight and spiral filaments, abscised 
 straight and spiral rod-like portions of filaments, the latter pro- 
 vided with cilia and described under the name of Ophidomonas 
 (d), round Cocci or spores (e-k) and Zoogloea-aggregates of 
 these, make their appearance in just the same alternation as in 
 the two preceding genera, rods, Spirilla, and Cocci having in many 
 cases a swarming motion. The distinction between them and the 
 species of Crenothrix and Cladothrix lies chiefly in the presence 
 of sulphur in their structure, and in the motility of the filaments 
 which, like those of Crenothrix, are never branched. 
 
 Beggiatoa alba, Vaucher, the most common species, has 
 colourless filaments, attached when quite intact to solid bodies 
 but easily breaking off from them and thus set free, and varying 
 in thickness from i to 5 p. The filaments consist of cells of 
 more or less elongate cylindrical to flat disk-like form, the latter 
 occurring especially in the thicker specimens. They have no 
 distinct sheath clothing the row of cells ; moreover, while the pro- 
 toplasm of Crenothrix and Cladothrix is uniformly clouded or 
 finely granular, in Beggiatoa alba it has disseminated through its 
 substance comparatively thick round highly refringent grains, 
 with a dark contour therefore, and composed of sulphur, as 
 Cramer has shown. Similar sulphur-grains are also present in 
 the non-filamentous states or forms assigned here by Zopf. 
 Their number is not the same in different filaments ; in some 
 filaments (c) but few are to be seen, and in parts of them 
 they may even be entirely wanting. In most filaments they are 
 present in large numbers, so large sometimes that they en- 
 tirely conceal the structure of the thread, which looks like a 
 rod having its uniformly clouded protoplasm traversed by a 
 dense mass of granules with a black outline. It is only by the 
 use of reagents which largely withdraw the water of the cells 
 that it is possible to distinguish them (). 
 
 Again, the filaments usually exhibit active movements, such as 
 
8o Lectures on Bacteria. [$ vm. 
 
 are known in the green Oscillatorieae, which have been noticed 
 already several times, and which are undoubtedly the near allies 
 containing chlorophyll of the species of Beggiatoa and of the 
 arthrosporous Bacteria. The movements consist in progression 
 in the line of the axis of the filament in one direction, or in 
 opposite directions alternately, together with rotation in a path 
 which forms the outline of a very pointed cone, or of a 
 double cone such as is described in the case of rod-shaped 
 Bacteria. These movements, when hastily observed, appear 
 to be gliding in a forward direction, while the ends of 
 the filaments swing hither and thither in the manner of a 
 pendulum. Sometimes also the filaments become curved, and 
 then often straighten themselves again with a jerk, showing their 
 great flexibility throughout their entire length. 
 
 Several other species of Beggiatoa are known : B. roseo-per- 
 sicina, distinguished by its rose-red to violet colour, and also 
 said to be pleomorphous, its Zoogloeae, according to Zopf, 
 being Cohn's Clathrocystis roseo-persicina ; B. mirabilis, Cohn, 
 known only in the filamentous form, a gigantic species 20-30 /A 
 in thickness; B. arachnoidea, Roth, and some others. Apart 
 from the differences indicated, all these agree with B. alba in the 
 characteristic marks, especially in the presence of sulphur-grains. 
 
 B. alba is one of the most common inhabitants of our waters. 
 It is found in the water of marshes, in the waters that flow 
 from manufactories, in hot sulphur-springs, and in these places 
 often in company with Cladothrix, and in the sea on shallow 
 coasts. B. roseo-persicina is less common in these localities ; 
 the other species mentioned above are known only as coming 
 from the sea. The species of Beggiatoa live on the decompos- 
 ing remains of organised bodies, especially plants; they are, 
 therefore, chiefly found at the bottom of water, where such objects 
 accumulate. They form there, when largely developed, slimy 
 membranous coverings or films of flocculent matter, which are 
 either white in colour or vary from rose to brown-violet, as in 
 B. roseo-persicina. 
 
viii.] Aquatic Saprophytes. Beggiatoa. 81 
 
 The species of Beggiatoa are said to have the peculiar power 
 of reducing the sulphates contained in the waters which they 
 inhabit, especially sodium sulphate and gypsum, setting free the 
 sulphur and sulphuretted hydrogen. That the living protoplasm 
 is the seat of this process is shown by the appearance in it 
 of the sulphur-grains. The form- 
 ation of sulphuretted hydrogen 
 causes first the precipitation of iron 
 sulphide in the slime inhabited 
 by Beggiatoa, which is thereby 
 turned black, and then the presence 
 of sulphuretted hydrogen, either 
 dissolved in the water or set 
 free by evaporation, gives rise to 
 the well - known odour, and may 
 have a noxious effect on the 
 animals inhabiting the water. The 
 ' white ' ground in the Bay of Kiel, 
 for example, covered by species 
 of Beggiatoa, is also called the 
 ' dead ' ground, because it is 
 avoided by fishes, though not by 
 all animals (37). These plants 
 therefore play a peculiar and 
 important part in the economy of Fi S- 7- 
 
 nature and of mankind. According to the statements of some 
 
 Fig. 7. Beggiatoa alba, Vaucher. a portion of a stout living filament. 
 b fragment of the same after treatment with alcoholic solution of iodine show- 
 ing the segmentation into cells, c a very thin living filament from the same 
 preparation as a. d motile spiral form (Ophidomonas). e-h formation of 
 spores ('Cocci') by successive division of the segment-cells of a stout filament 
 (e). The lumen of each spore is nearly filled up by a grain of sulphur. Inf 
 the division has advanced further than in e. g breaking up of the filament 
 into groups of spores, h the spores isolated. *, k spores appearing to 
 germinate ( ), in a state of motion, a-c magn. 600 times, but drawn a 
 little too large, </ 540 times, e-k 900 times, d-k after Zopf. 
 
82 Lectures on Bacteria. [$ vm. 
 
 observers, they share this part with other plants which are green 
 and are related to the Oscillatorieae and Ulothricheae (25, p. 769). 
 The forms which have now been described are the largest, 
 but by no means the only, representatives of the aquatic Bac- 
 terium-flora. 
 
 The Spirilla which live in bog-water are remarkable forms, 
 and may be briefly illustrated here by two examples. Spirillum 
 Undula, Cohn (Fig. 8, A), forms small spirally-twisted rods of about 
 i p. in thickness. The width of the spiral in dead specimens is 
 about 3 ft, three times therefore the diameter of the cell, the height 
 
 of a turn of the spiral 5-6 n 
 (4-5 ^ according to Cohn). 
 Each individual is usually 
 formed of from ii to 2 
 
 turns only of the spiral ; 
 
 p. 8 when it has reached this 
 
 length it divides transverse- 
 ly in the middle into two. According to Cohn 3 turns of the 
 spiral are only rarely attained. The rod consists of segment- 
 cells, which, as far as can be determined, are immediately after 
 division about as long as a half turn ; they separate from one 
 another as soon as they are of this size (a\ or after longer 
 growth. 
 
 Spirillum tenue, Cohn (Fig. 8, J5), is more slender and more 
 closely twisted than S. Undula, and has several connected turns 
 of the spiral, usually 3, 4, or 6. The length of each of the 
 segment-cells which compose the spiral is at the time of division, 
 as far as I was able to determine, about half a turn, the same 
 therefore as in S. Undula. 
 
 No other phenomena of development than growth and division 
 of the rods have been perceived in these two species, even during 
 a cultivation of some months' duration; they both remain 
 
 Fig. 8. A Spirillum Undula, Cohn ; at a separation into two segment- 
 cells. B Spirillum tenue, Cohn; three specimens of different lengths. 
 Magn. 600-700 times. 
 
ix.] Aquatic Saprophytes. Spirillum. 83 
 
 constant in their forms and distinctions. They are often found 
 by themselves in the waters of bogs ; when 'they occur in large 
 quantities, and comparatively unmixed with other species, they 
 form dense swarms which, in S. Undula especially, are of a 
 beautiful dark reddish-brown colour. Single live rods are, 
 under the microscope, colourless and homogeneous. When 
 killed and treated with colouring reagents (iodine, anilin-dyes), 
 they exhibit a remarkable separation in the case of both species 
 into short irregular transverse zones of alternately darker and 
 lighter colour a phenomenon which must not be confounded 
 with the transverse segmentation into distinct cells mentioned 
 above. Finally, both species are distinguished by the extreme 
 vivacity of their movements, and dart like meteors, says Cohn, 
 across the field of vision, the slender Spirillum tenue affording 
 in this way a very elegant display. 
 
 Many other forms of the kinds previously described, and 
 among them of endosporous Bacilli, might be mentioned as 
 living in water. We still desiderate such investigation of these 
 forms as would enable us to give a more exact account of them 
 and of the decompositions which they may effect ; the scattered 
 particulars which are known of them have no interest for us on 
 the present occasion. Of the germs of Bacteria which may be 
 found even in the purest waters when exposed to the air and 
 to dust I have already spoken in the fifth Lecture. 
 
 IX. 
 
 Saprophytes which, excite fermentation. Fermentations 
 of urea. Nitrification. Acetous fermentation. Vis- 
 cous fermentations. Formation of lactic acid. Kefir. 
 Bacillus Amylobacter. Decompositions of proteid. 
 Bacterium Termo. 
 
 WE have now to consider saprophytic forms which are known 
 to be the causes of distinct processes of decomposition or 
 fermentation, and as examples of more general interest we select 
 
 6 2 
 
84 Lectures on Bacteria. [$ ix. 
 
 for closer examination the Micrococcus of urea, the nitrifying 
 Bacteria, the mother of vinegar, the Bacteria of lactic acid- 
 fermentation, of butyric acid-fermentation, and of the viscous 
 fermentation of carbohydrates and other bodies, and, lastly, the 
 Bacteria of the decompositions of proteids. 
 
 i. The normal urine of men and carnivorous animals if kept 
 exposed to the air acquires an alkaline and ammoniacal smell ' 
 in place of the acid reaction present in it when fresh. The 
 cause of this is, that the urea takes in water and is converted 
 into ammonium carbonate. The originally clear fluid becomes 
 clouded by the presence, as examination shows, of a number of 
 lower organisms, among which there may be a variety of Fungi 
 and Bacteria. Pasteur first proved that one of these Bacteria, 
 Micrococcus Ureae, Cohn, was the exciting cause of this process 
 of fermentation in urea (38 ; 25, p. 697), by showing that the 
 Micrococcus, if grown pure and cultivated in a pure nutrient 
 solution containing urea, causes the same decomposition in it 
 as in urine. 
 
 The Micrococcus (Fig. 9) consists of small round cells about 
 0-8 p in diameter, which usually, though not in- 
 variably, remain connected together in rows often 
 of more than 12 cells. These rows are in many 
 cases curved and bent in an undulating manner, 
 and are often ultimately wound into coils or small 
 g ' 9 * Zoogloeae as they may be termed, in which the cells 
 appear to be irregularly heaped together. At the first beginning 
 of a culture the cells, according to von Jacksch, are cylindrical, 
 though not very much longer than they are broad ; they retain 
 this shape for some time, firmly united together in genetic 
 connection, forming therefore rod-like rows of short cylindrical 
 cells, and afterwards become rounded off. We may therefore, if we 
 please, speak of a ' rod-form/ but we shall not gain in clearness 
 by so doing. No distinct spores have been observed in this 
 
 Fig. 9. Micrococcus Ureae, Cohn, from decomposing urine. Cells 
 separate or united in rows ( = Streptococcus). Magn. noo times. 
 
ix.] Fermentation of urine. Nitrification. 85 
 
 Micrococcus. Leube has recently demonstrated the existence 
 of four quite distinct species of Bacteria, in addition to the 
 Micrococcus just described, producing the same effects. 
 
 Micrococcus Ureae, as we learn from experiment, requires a 
 supply of oxygen for its vegetation. It can hardly therefore 
 be the cause of the alkalisation of the urine inside the bladder, 
 which has been observed in some affections of the bladder and 
 is supposed to be an effect of it, for the oxygen required is not 
 present. But numbers of small Bacteria are found in urine in 
 this diseased alkaline condition, and it must be assumed that 
 having found their way spontaneously or forcibly, as for instance 
 by means of the catheter, through the urethra into the bladder 
 they are the exciting cause of the decomposition in question. 
 It must accordingly be further assumed, that other species which 
 are anaerobiotic have the power of producing fermentation in 
 urine, or processes similar to it. Leube's species appear from 
 the accounts given of them not to be anaerobiotic. Miquel 
 (15, vol. for 1882) has in fact discovered a very delicate rod- 
 form occurring in dust, which he names Bacillus Ureae and 
 which vegetates anaerobiotically, converting urea into ammo- 
 nium carbonate in the same way as Micrococcus Ureae. 
 
 We learn from van Tieghem that hippuric acid is converted 
 into benzoic acid and glycocol in the urine of herbivorous 
 animals by a Micrococcus, which is perhaps identical with 
 Micrococcus Ureae, but requires further investigation. 
 
 2. In connection with the forms which change urine into 
 ammoniacal compounds, we may now turn to the consideration 
 of nitrification, the oxidation of compounds of ammonium into 
 nitrates, such as occurs on a large scale in the formation of 
 saltpetre, in so far as this also is due, according to the observa- 
 tions of Schlossing and Miintz (25, p. 708 ; 39), to the vegeta- 
 tion of small Bacteria. The phenomenon occurs in moist soil 
 penetrated by air and containing compounds of ammonium with 
 small quantities of organic matter and basic substances, for 
 example, salts of calcium. It may be induced artificially in 
 
86 Lectures on Bacteria. [ ix. 
 
 nutrient solutions containing compounds of ammonium, if a 
 small quantity of soil is added at a suitable temperature, the 
 optimum being 37 C., and with constant access of air. 
 
 Thus the formation of saltpetre is a result of the vegetation 
 of Bacteria ; it ceases when these are killed ; it also commences 
 when these Bacteria, artificially reared, are placed by themselves 
 without soil in the proper nutrient solution. From this we must 
 conclude that we have here an oxidation produced by the Bacteria 
 which are widely diffused in the superficial layers of a moist soil. 
 
 The morphology of these Bacteria is not yet clearly ascertained. 
 According to the above-named writers, the individual organism 
 is a very small delicate Micrococcus, somewhat resembling 
 M. aceti, and van Tieghem, in his text-book, has named it 
 M. nitrificans. But the appearance assumed by this form is not 
 clear from the descriptions, and Duclaux speaks of a mixture of 
 different forms. The importance of the processes calls for a 
 more exact study of them, that is, of the question, whether nitrifi- 
 cation is the exclusive function of a distinct species, or of several 
 species and their combinations. 
 
 3. Acetous fermentation (25, p. 504; 40, 41,42). If an acid 
 nutrient solution containing a small percentage of alcohol is 
 exposed to the air at a temperature of about 30-40 C., vinegar 
 is formed in it, that is, the alcohol is oxidised into acetic acid. 
 The fluid is at the same time more or less clouded, and its sur- 
 face covered with a thin colourless membrane. This membrane 
 consists in most pure cases of mother of vinegar, Micrococcus 
 aceti, Bacterium aceti (Arthrobacterium aceti ; Mycoderma aceti 
 in Pasteur's earlier nomenclature). Pasteur showed twenty- 
 five years ago that this Bacterium lives and grows on the organic 
 and mineral substances contained in the solution, and absorbing 
 oxygen from the air oxidises the alcohol into acetic acid. The 
 exact proof was obtained by adding 4 per cent, of alcohol and 
 1-2 per cent, of acetic acid to pure nutrient solutions of the 
 kind described on pages 61 and 67, and then introducing into 
 the liquid an infinitesimal quantity of membrane of mother of 
 
ix.] Acetous fermentation. 87 
 
 vinegar. In the proper temperature, and with free access of 
 atmospheric air, the mother of vinegar developes into the mem- 
 brane described above, and as this takes place the alcohol in 
 solution is converted into acetic acid. 
 
 The various methods used in the arts for the preparation of 
 vinegar, into the details of which we do not here enter, are cul- 
 tures of Micrococcus aceti at the proper temperature, and with 
 exposure to the air under regulations which vary in each par- 
 ticular case. The mixtures from which the vinegar is to be 
 prepared beer, wine, &c., with addition of previously formed 
 vinegar, have the essential characters of nutrient solutions as 
 described above. The vinegar of commerce is a diluted solution 
 of acetic acid, and contains a larger or smaller number of the 
 Micrococcus aceti. Germs of this organism are also diffused 
 elsewhere, and in particular are never wanting in the vessels 
 used for the preparation and storing of alcoholic fluids. When 
 these turn acid, owing to careless management, it is in part at 
 least owing to the activity of the Micrococcus. M. aceti, like 
 M. Ureae, is as far as we know at present an arthrosporous 
 Bacterium, and resembles the latter in shape (Fig. 10). It con- 
 sists usually, and always in the normal vegetating stage, of 
 cylindrical cells, which are not much longer than broad, and 
 have a transverse diameter of about o-8-i /*. The cells multiply 
 by the usual process of transverse division, and often remain 
 united together in rows forming long filaments ; in older cultures 
 they are often thrust out of the filament but are held together 
 by jelly. With this short-celled Micrococcus-form cell-rows 
 often occur, in which some cells are in the form of long rods, 
 others not only several times longer than broad, but also fusiform 
 and so swollen in a bladder-like manner that their greatest 
 breadth may be more than four times the diameter of the ordinary 
 cells. No one would suppose these inflated cells to belong to 
 the small ones, if they did not usually occur with them, either 
 singly or several together, as members of the same genetic rows 
 and connected with them by a variety of intermediate forms. 
 
88 Lectures on Bacteria. [ ix. 
 
 Cases of this kind have been observed also in other Bacteria ; 
 these are the cells with which we made acquaintance before on 
 page 10 under Nageli's name of involution-forms. Whether they 
 are really retrograde states, as this name would express, or 
 diseased forms, I shall not undertake to say in the case of 
 the Micrococcus aceti. They certainly do not appear at all in 
 some cultures, or only one by one, while in others they are ex- 
 traordinarily numerous, and in the latter case I could never find 
 that they gave the 'impression of being incapable of further 
 development.' Positive statements, however, are at present no 
 more possible respecting their significance in the history of 
 development than they are respecting the conditions of their 
 presence or absence. 
 
 A Micrococcus has been found by E. Chr. Hansen, and named 
 by him M. Pasteurianus, which behaves in every respect in 
 the same way as M. aceti, except that its cells 
 throughout the successive generations show the 
 blue reaction of starch with iodine (see page 5), 
 while the ordinary M. aceti is coloured yellow 
 by that reagent. This fact shows at once that 
 M. aceti although certainly the usual is not the 
 only vinegar-forming species. In fact the power 
 of producing acetic acid has been observed in 
 some other Bacteria, which are, however, comparatively unim- 
 portant to us for our present purpose. 
 
 Micrococcus aceti has the power not only of producing but 
 also of destroying vinegar. When it has oxidised all the alcohol 
 of a fluid into acetic acid, it may continue to develope, as 
 Pasteur showed, and by a further process of oxidation convert 
 the acetic acid into carbonic acid and water, the final products 
 of all decomposition. 
 
 Fig. 10. Micrococcus aceti (mother of vinegar) ; roundish cells, single 
 and united in rows, also rows of elongated rod-like and fusiform or swollen 
 flask-shaped members ; the latter from a culture at a temperature of 40 C. 
 Magn. 600 times. 
 
ix.] Viscous fermentation. 89 
 
 It does not strictly belong to our subject, but it is perhaps 
 not superfluous to remark that every white membrane which 
 makes its appearance spontaneously on the surface of a fluid 
 suitable for forming vinegar is not necessarily mother of vinegar. 
 The white and ultimately wrinkled film which usually forms on 
 beer or wine, is a well-known object, and to the naked eye looks 
 so like the membrane of vinegar as to be often mistaken for it. 
 But under the microscope it is distinguished from it by being 
 formed from a comparatively large Sprouting Fungus, Saccharo- 
 myces Mycoderma, which has no direct connection with the 
 formation of vinegar. On the contrary, it converts alcohol and 
 other bodies in solution by oxidation into carbonic acid and 
 water. Indirectly it may, indeed, in this way promote the for- 
 mation of vinegar by destroying any excessive amount of alcohol 
 and acid which would impede the development of the Micro- 
 coccus aceti, and so providing it with a substratum favourable 
 to its vegetation. 
 
 4. We now come to a series of examples of phenomena of 
 fermentation and decomposition produced by Bacteria in the 
 sugars and in the allied carbohydrates. When in the following 
 remarks we speak simply of saccharine solutions, it is always to 
 be understood that they contain also the constituents required 
 for nutrient solutions. 
 
 We must first of all say a word or two respecting the so-called 
 viscous fermentations (25, p. 572, 43, 44). The juices of plants 
 which contain sugar, such as onion and beet, when extracted 
 by crushing often assume a sticky viscous character, and produce 
 carbonic acid and in many cases also mannite. Organisms 
 also, to be described presently, make their appearance as a 
 sediment in the viscous mass. If a small portion of the sub- 
 stance is introduced into a suitable solution of cane-sugar which 
 was before free from germs, the same viscidity is caused in it 
 as the organisms develope. These must therefore be regarded 
 as the causes of the change. The organisms in question are, 
 according to Pasteur, of two kinds. The first is a Micrococcus 
 
90 Lectures on Bacteria. [$ ix. 
 
 very like M. Ureae and forming rows of bead-like cells ; by itself 
 it produces viscidity and mannite in the cane-sugar solution with 
 separation of carbonic acid. Secondly, cells of irregular shape 
 and somewhat larger size than those of the Saccharomyces of 
 beer-yeast (see page 98), and with morphological peculiarities, 
 which the descriptions which we have of them do not at all 
 clearly explain ; these cells are at all events not Bacteria, and 
 are said to cause viscidity only and to form no mannite in the 
 cane-sugar solution. The viscous substance itself, of which we 
 are here speaking, is stated to be a carbohydrate with the for- 
 mula of cellulose (C 6 H 10 O 5 ). 
 
 From these data, which it is true are still very imperfect, it 
 must be acknowledged that the disengaged carbonic acid and the 
 mannite are products of fermentation ; but the viscous substance 
 itself is more probably to be placed in the category of muci- 
 lagino-gelatinous cell-membranes, which are so common in Bac- 
 teria and Fungi and which we have already observed so often 
 in connection with the Zoogloeae ; it is therefore not a product 
 of the fermentation of the nutrient solution, but of the assimi- 
 lation of the organism which excites the fermentation. 
 
 This view is distinctly supported by the history of the 
 development and vegetation of Leuconostoc mesenterioides, the 
 frog- spawn-bacterium of sugar-manufactories, examined by Cien- 
 kowski and van Tieghem, which has the power of converting 
 large casks of the juice of the sugar-beet in a short space of 
 time into a mucilagino-gelatinous mass and thus of causing 
 considerable loss. Durin saw a wooden vat containing fifty 
 hectolitres of a 10 per cent, solution of molasses become filled 
 with a compact Leuconostoc-jelly in less than twelve hours. The 
 development of Leuconostoc was mentioned above on page 2 2 as 
 an example of an arthrosporous course of development, but a 
 more detailed description of it must now be given. See Fig. n. 
 
 The round spore-cell (d) germinates in a nutrient solution, 
 and appears at first to be surrounded by a gelatinous envelope 
 several times thicker than the spore itself (e). Then a simple 
 
ix.] Viscous fermentation. Leuconostoc. 91 
 
 filiform row of isodiametric cells is formed by the growth and 
 successive transverse division of the protoplasmic body, and the 
 envelope follows the longitudinal growth of the cells, forming a 
 thick, rounded, cylindrical sheath of the consistence of firm gela- 
 tine round the filament. The transverse walls also of the filament 
 in its young state are gelatinous, appearing as broad pellucid 
 partitions between the protoplasmic bodies and being continued 
 into the sheath on the outside (f-i}. The partitions disappear 
 in older filaments and the protoplasmic bodies are in contact 
 
 Fig. ii. 
 
 with one another (b). As the single filament developed from 
 a spore increases in length it forms successively stronger curva- 
 tures, which lay themselves in loops round each other and round 
 
 Fig. ii. Leuconostoc mesenterioides, Cienkowski. a sketch of a Zoogloea. 
 b section through a full-grown Zoogloea before the commencement of spore- 
 formation, c filament with spores from an older specimen, d isolated ripe 
 spores, e-i successive products of germination of the spores sown in a 
 nutrient solution. Order of development according to the letters. In e the 
 two lower specimens show fragments of the ruptured spore-membrane on 
 the outer surface of the gelatinous envelope indicated by dark strokes. 
 i portion of the gelatinous body from h divided into short members, and 
 with the members separated from one another by pressure, a natural size, 
 other figures magn. 520 times. After van Tieghem in Ann. d. Sc. nat. 
 ser. 6, VII. 
 
92 Lectures on Bacteria. [$ ix. 
 
 other filaments. Growth is also accompanied with separation 
 of the originally elongated gelatinous filaments into shorter 
 transverse sections, which are always surrounded by the sheath 
 and remain firmly attached to one another (*). Closely twisted 
 coils are thus produced of the size of or larger than a hazel-nut 
 (a), forming the compact gelatinous bodies mentioned above 
 which accumulate and fill the casks. Sections through older gela- 
 tinous bodies appear to be divided from the edges of the sheaths 
 into chambers in which the curved cell-rows lie (6). When the 
 development is completed, and the nutrient solution exhausted, 
 the gelatinous sheaths deliquesce, the cell-rows separate, and 
 most of the cells die. But previously to this single cells, not 
 occurring in any particular order in the row, develope into 
 distinct spores, becoming a little larger than the rest, and sur- 
 rounding themselves with a firm non-gelatinous membrane, the 
 outer coat of the spore (c). It was from these spores that we 
 set out in the description ; but every living portion of a filament 
 that from any cause becomes separated from the connection 
 may develope into a new gelatinous body. The vegetating 
 protoplasmic bodies are, according to van Tieghem, 0-8-1-2 /M 
 in thickness, the sheaths 6-20 /n, the spores 1*8-2 //. 
 
 In the germination of the spore the gelatinous sheath origi- 
 nates (e) as a newly formed inner layer of the cell-wall, or by the 
 considerable increase in thickness of a pre-existing inner layer ; 
 the outer coat of the spore then bursts into pieces. This shows 
 decisively that the sheath is a product of assimilation, a growing 
 part of the growing filament. The gelatinous substance has 
 the same chemical composition as the mucilage of viscous fer- 
 mentation. The material for its formation is of course supplied 
 by the sugar of the solution. In van Tieghem's cultures 
 of Leuconostoc in a solution of glucose, air being admitted 
 and the fluid prevented from becoming strongly acid, about 
 40 per cent, of the sugar which disappeared was expended 
 in the formation of the Leuconostoc itself; the greater part of 
 the remainder was converted by combustion into carbonic acid 
 
ix.] Lactic acid-fermentation. 93 
 
 and water without any sensible development of gas. The culti- 
 vation of Leuconostoc in solution of cane-sugar soon resulted in 
 the splitting (inversion) of the sugar into glucose and laevulose, 
 and for this reason it is so highly detrimental to the fabrication 
 of cane-sugar ; the sugar then disappears as in the first experi- 
 ment, the glucose first, and about 40-45 per cent, of the sugar 
 which disappears is expended in the formation of the Leuconostoc. 
 
 A similar formation of mucilage to that of the viscous 
 fermentation of saccharine solutions, is seen in the ropiness 
 of beer and wine, in which condition they are capable of 
 being drawn out into filaments. These phenomena also are 
 accompanied, or doubtless caused, by the formation of Micro- 
 cocci united together in rows, and the slime may very well have 
 the same origin and morphological significance as the jelly of 
 Leuconostoc. It may be observed in passing that other so- 
 called ailments of beer and wines are caused by Bacteria, but 
 we cannot enter into any further description of them here 1 . 
 
 5. The old method of inducing ordinary lactic acid fermen- 
 tation (25, 45) of the different kinds of sugar is by adding sour 
 milk or cheese to a fermentable solution and keeping it exposed 
 to the air at a temperature of 40-50 C. Calcium carbonate 
 or zinc-white must also be added in order to throw down the 
 lactic acid as it is disengaged, because the fermentation ceases 
 as soon as the acid content of the fluid exceeds a certain 
 amount. 
 
 Pasteur first showed that a particular Bacterium, and others 
 perhaps along with it, was introduced with the cheese or sour 
 milk, and that it vegetates in the fluid, especially in the sediment 
 at the bottom, and acts as a ferment. It appears in the form 
 of minute cylindrical cells, which immediately after division are 
 scarcely half as long again as they are broad, and average o'5 p. 
 in thickness. After each division they usually soon separate 
 from one another, rarely remaining united, and forming short 
 
 1 See Pasteur, Etudes sur le vin, Paris, 1866, and Etudes sur la biere, 
 Paris, 1872. 
 
94 Lectures on Bacteria. [$ ix. 
 
 rows ; portions of the transverse partition- walls are plainly seen 
 and are indicated by a slight constriction. They have no power 
 of independent movement. In form, therefore, this species resem- 
 bles the Bacterium of vinegar and may be called Micrococcus 
 lacticus, as has been done by van Tieghem. Hueppe, however, 
 states that there is a formation of spores, if I understand him 
 aright, after the endosporous type. If this is confirmed, the 
 Bacterium of lactic acid is a very small Bacillus in our use of 
 the term, and must be so named. 
 
 It is evident that this Micrococcus or Bacillus is always 
 present in milk, not of course when it comes from the udder, 
 but as soon as it is in use. The germs of the organism are 
 diffused to such an extent in the cattle-stalls and in the vessels 
 of the dairy that it never fails to be developed. This is why 
 milk turns sour, because the Bacterium excites lactic acid- 
 fermentation of the sugar contained in the milk; and when 
 the acidification has reached a certain point, the lactic acid 
 causes the homogeneous gelatinous coagulation of the casein, 
 which is characteristic of good buttermilk. 
 
 Further physiological peculiarities of this Bacterium have been 
 described in detail in Hueppe's careful treatise, and should be 
 studied there. 
 
 In the Bacillus or Micrococcus lacticus which has now been 
 described we have made acquaintance with a very widely diffused 
 and active lactic acid-ferment, but it is by no means the only 
 one. On the contrary, the number of species of Bacteria which 
 form lactic acid in saccharine solutions or in milk appears to 
 be more than usually large. Hueppe alone mentions five, and 
 all Micrococci ; one of these is known to us as M. prodigiosus of 
 the blood-portent mentioned on page 14. Two others Hueppe 
 discovered to be the exciting cause of the lactic acid which 
 occurs in the human mouth, while he found the Bacillus first 
 described only occasionally in the mouth. We still wait for 
 closer investigation into most of these forms, and into their 
 operation as ferments. It is, however, already plain that on all, 
 
J ix.] Kefir. 95 
 
 or almost all, occasions on which lactic acid makes its appear- 
 ance in considerable quantities we may expect to find a ferment- 
 organism, and indeed a Bacterium which produces it, but this 
 need not always be the one form, described above as that of 
 ordinary acidification of milk. It is well to call particular 
 attention to this point on account of the wide diffusion of lactic 
 acid, for example in human food, whether this be purposely 
 made sour, -as in ' sauerkraut ' and the like, or is a case in which 
 the turning sour indicates decomposition, as in soured vegetables 
 or beer, so far as the effect in the latter case is not due to the 
 presence of acetic acid. 
 
 6. This will be the best place to recur briefly to the Bac- 
 terium of kefir mentioned above on page 13, which is connected 
 with an interesting change in milk. It was discovered by E. Kern 
 in 1882 (46). Kefir or kephir is the name of a drink, a fluid 
 effervescing kind of sour milk containing a certain amount of 
 alcohol, which the inhabitants of the upper Caucasus prepare 
 from the milk of cows, goats, or sheep, and therefore not to be 
 confounded with the koumiss obtained by the Nomads of the 
 Steppe originally from mares' milk, with which we are not at 
 present concerned. The drink is prepared by adding to the 
 milk the bodies described above as a beautiful example of 
 Zoogloeae, which bear the name of kefir-grains. The Cauca- 
 sians make use in this process of leathern bottles to hold the 
 milk, the more polished European employs less objectionable 
 glass vessels. The recipe followed by the latter is mainly as follows. 
 
 Living and thoroughly moistened kefir-grains are added to 
 fresh milk in the proportion of i volume of the grains to about 
 6-7 volumes of milk. The mixture is exposed to the air for 
 twenty-four hours at the ordinary temperature of a room, pro- 
 tected from dust by a loose covering only, and is frequently 
 shaken. At the end of twenty-four hours the milk is poured 
 off from the grains, which may be employed again for a fresh 
 preparation. The milk itself, which we will term ferment-milk, 
 is then mixed with twice the quantity of fresh milk, put into 
 
96 Lectures on Bacteria. [$ ix. 
 
 bottles well corked and frequently shaken. The bottled sour 
 milk, which is more or less highly effervescent, is fit to drink 
 in one or more days. It has the somewhat acid taste indicated 
 by its name, and contains an amount of carbonic acid varying 
 according to the temperature and the duration of the fermenta- 
 tion, but sometimes sufficient to burst the bottles or drive out 
 the corks, and, as has been already said, a certain amount of 
 alcohol, which in the cases examined in Germany was less than 
 i per cent, but according to other accounts may be 1-2 per cent. 
 
 The changes in the milk which produce the drink here de- 
 scribed are brought about by the combined activity of at least 
 three ferment-organisms. The kefir-grains, as has been already 
 stated (page 13), consist chiefly of the gelatinous filamentous 
 Bacterium which has been named by Kern Dispora caucasica ; 
 intermixed with this organism and enclosed in the tough Zoo- 
 gloea are numerous groups of a Sprouting Fungus, a Saccharo- 
 myces, resembling the yeast-plant of beer; thirdly, there is 
 the ordinary Bacterium of lactic acid, which partly adheres to 
 the grains in company with some unimportant Fungi and other 
 impurities, and partly is introduced each time with the fresh 
 milk. 
 
 We know at least enough of the ferment-effects of these 
 organisms or of their near allies to enable us to form a probable 
 idea of the course of the changes which have been described. 
 The acidification is caused by the conversion of a portion of the 
 milk-sugar into lactic acid by the Bacterium of that acid. The 
 alcoholic fermentation, that is, the formation of alcohol and of a 
 large part at least of the carbonic acid, is indebted for its 
 material to another portion of the milk-sugar, and for its exist- 
 ence to the fermenting power of the Sprouting Fungus. The 
 kefir-grain, like its constituent the Sprouting Fungus working by 
 itself, gives rise to alcoholic fermentation in a nutrient solution 
 of grape-sugar, though of a less active kind than that caused 
 by the Sprouting Fungus of beer-yeast. But alcoholic fermenta- 
 tion is produced in milk-sugar as such neither by Sprouting 
 
I ix.] Kefir. 97 
 
 Fungi with which we are acquainted, nor, as experiment has 
 shown, by those of which we are speaking. To make this 
 fermentation possible, the sugar must first be inverted, split 
 into fermentable kinds of sugar. According to Nageli(9, p. 12), 
 the formation of an enzyme which inverts milk-sugar is a 
 general phenomenon in Bacteria, and Hueppe has shown that 
 it is probable in the case of his Bacillus of lactic acid in par- 
 ticular; the inversion required in this case to enable the 
 Sprouting Fungus to set up alcoholic fermentation is the work 
 therefore of the Bacillus of lactic acid, or of the Bacterium of 
 the Zoogloea, or of both. 
 
 Lastly, it is to be observed that the kefir is in the fluid state. 
 Coagulation of the casein does indeed take place, but either it is 
 from the first not in the homogeneous gelatinous form of 
 ordinary sour milk but in small lumps and flakes suspended in 
 serum, or the gelatinous coagulations which are sometimes 
 present at first are soon partially dissolved. It is evident then 
 that the casein, which has already been coagulated, is partially 
 liquefied (peptonised). This must be ascribed to the enzyme 
 formed by the Bacterium of the Zoogloea, because according to 
 our present knowledge the Bacterium of lactic acid has no power 
 to peptonise casein or otherwise liquefy it. 
 
 This view, which corresponds in all important points with 
 Hueppe's brief communication on the subject, is in accordance 
 with the remarkable fact that the ferment-milk, by means of 
 which the kefir is prepared, contains a large number of actively 
 growing cells of a Sprouting Fungus and of Bacteria of lactic 
 acid, but no Bacteria of the Zoogloea, or only small and doubt- 
 ful quantities of them. The grains as a rule strictly retain 
 these, while they part with the sprouting cells to the milk. There 
 is obviously no objection to the supposition that enzymes pro- 
 duced from the grains pass over into the ferment-milk and co- 
 operate with it. 
 
 In this way, as I have said, we may explain the formation of 
 kefir, and I gave this account of it in the first edition of 
 
 H 
 
98 Lectures on Bacteria. [ ix. 
 
 this work while calling attention to the want of precise 
 investigation. 
 
 But A. Levy, of Hagenau, has recently discovered that the 
 effervescing alcoholic kefir may be obtained without any 
 kefir-grains, but simply by shaking the milk with sufficient 
 violence while it is turning sour. A trial convinced me of the 
 correctness of this statement. The kefir obtained by shaking 
 was not perceptibly different in taste or other qualities from the 
 kefir of the grains, and the determination of the alcohol, kindly 
 made for me by Professor Schmiedeberg, gave i per cent, 
 in some specimens of the former kind and 0-4 per cent, in 
 one of the latter ; sour milk not shaken contained no trace of 
 alcohol or only a doubtful one. Our former explanation there- 
 fore must be abandoned, and there is no other ready at present 
 to take its place; but the case is full of instruction for our 
 warning. 
 
 Turning now for a moment to the life-history of the kefir- 
 
 grains, we may briefly remark 
 with respect to the Saccharo- 
 myces, that it grows in the 
 sprout-form observed in the 
 Saccharomyces of beer-yeast, 
 partly forming groups or nests 
 inside or on the surface of 
 the grains, partly separating 
 from them and entering the 
 Fi &' I2 - surrounding fluid. It is on 
 
 an average smaller and narrower than Saccharomyces Cere- 
 visiae, but some idea of its form may be gathered from a figure 
 here reproduced of that Fungus which it very closely resembles 
 (Fig. 12). Of the Bacterium, of which the grains chiefly consist, 
 I believe that we also know only the vegetative development. 
 
 Fig. 12. Saccharomyces Cerevisiae. a cells before sprouting, b-d 
 sproutings in fermenting saccharine solution (sequence of development 
 according to the letters). Magn. 390 times. 
 
$ ix.] Kefir. Bacilhis Amylobacter. 99 
 
 It appears, as has been already said, in the form of small slender 
 rods united into filaments, which are closely interwoven and held 
 together in Zoogloeae by means of a jelly. 
 
 The source of the grains has not been traced further back 
 than the leather milk-bottles of the mountaineers ; their place of 
 birth is still unknown. They come to us in the dry state, and 
 are kept in this manner in the Caucasus also. They must be 
 dried quickly, and the best plan is to dry them in the sun. 
 Much of the dry imported material is dead when it comes, as 
 far as my experience goes. The softened living grain grows 
 slowly in the milk, as we have already seen (page 59), with 
 uniform increase in size and multiplication of all its parts. 
 This growth is accompanied by the separation from time to time 
 of single lobes of different sizes from the whole, and thus the 
 number of the grains increases. From isolated observations I 
 regard it as possible that Dispora-cells sometimes issue from a 
 grain, and may then develope into kefir-grains, but this is not 
 certain. Distinct formation of spores has not yet been observed. 
 Kern it is true has not only described such a formation, but 
 named the Bacterium of kefir Dispora, because two spores are 
 formed each time in a rod, one at each end. After repeated 
 observation I have never seen anything of the kind, though I 
 have very often seen figures which answer to Kern's represent- 
 ations, and which are due to the circumstance that a rod or 
 portion of a filament is curved and its middle portion lying 
 horizontally is seen in its length, but one or both of its 
 extremities which bend away from the horizontal plane are 
 viewed in cross-profile. It is by such appearances that Kern 
 has allowed himself to be misled. If we allow the name 
 Dispora to be used provisionally, it must not be forgotten that 
 the character which it is intended to express does not really 
 exist. 
 
 7. We will close the series of examples of the Bacteria which 
 excite characteristic fermentations in non-nitrogenous com- 
 pounds by the consideration of a species of Bacterium which is 
 
 H 2 
 
ioo Lectures on Bacteria. [ ix. 
 
 one of the most widely diffused, and most important and varied 
 in its powers of decomposition, the Bacillus of butyric acid, 
 known as B. Amylobacter, van Tieghem, B. butyricus, Clostri- 
 dium butyricum, Prazmowski (22, 47, 48), and by some other 
 names. I think that I ought also to refer Bacillus butylicus of 
 Fitz to this species, though it must be remembered that this 
 species as at present established may perhaps be divided into 
 several on further investigation. 
 
 Bacillus Amylobacter (Fig. 1 3) is nearly i p. in thickness, and 
 vegetates in the form of slender cylindrical rods united at 
 most into short rows, and usually in a state of active movement. 
 It is easy to characterise morphologically, because the sporo- 
 genous cells swell out till each becomes 
 fusiform and then produce inside the part 
 which is most enlarged an elongate ovoid 
 spore with rounded ends and sometimes 
 slightly bent, surrounded with a broad 
 
 ^ i 1 I S gelatinous envelope, and much shorter and 
 
 1 m j B usually much narrower than the swollen part 
 
 of the cell in which it is formed. It is also 
 distinguished by the starch-reaction or 
 granulose-reaction described on page 18, 
 which is usually manifested by the cells 
 before the spores are formed, and by its 
 habit, since it does not usually aggregate 
 and form distinct membranes or larger Zoogloeae, and at the 
 period of spore-formation often appears in the form of the motile 
 rods with capitate end, which were likewise noticed on a former 
 occasion (see page 17). Otherwise Bacillus Amylobacter is very 
 morphous; the most different special forms of sporogenous 
 
 Fig. 13. Bacillus Amylobacter. Motile rods, some cylindrical and 
 without spores, some swollen into various special shapes and with spore- 
 formation in the swelling, s mature spore with broad gelatinous envelope 
 and isolated by the deliquescence of their mother-cells. Magn. 600 times, 
 with the exception of s which is more highly magnified. 
 
ix.] Bacilhis Amylobacter. 101 
 
 cells make their appearance irregularly mixed up together and 
 connected with one another, as Fig. 13 shows. 
 
 In its mode of life, Bacillus Amylobacter is a type of Pasteur's 
 anaerobia (page 54), though the possibility of its vegetating 
 in the presence of oxygen is not excluded. Living in this 
 manner it is first of all the chief promoter of butyric acid- 
 fermentations of sugars, that is, of fermentations in which 
 butyric acid is the primary product and is accompanied by other 
 products which vary greatly according to the special material, 
 as is shown by the researches of Fitz. It may also be assumed 
 that it is this species which causes butyric acid-fermentation 
 in lactates, though an objection brought by Fitz against this 
 view has not yet been quite removed. In this special cha- 
 racter of the ferment of butyric acid B. Amylobacter plays 
 an important part in human economy, whether as the cause of 
 fermentation in acid articles of vegetable food which in this case 
 rapidly rot, or of the butyric acid-fermentation which is essential 
 to the ripening of cheese. 
 
 Bacillus Amylobacter is also a specially active agent, as van 
 Tieghem has shown, in the decomposition of decaying parts of 
 plants by destroying the cellulose of the cell-membrane. It 
 does not attack all cell-membranes, not for example suberised 
 membranes, those of bast-fibres, of submerged water-plants, of 
 Mosses and many Fungi ; on the other hand, the membranes of 
 fleshy and juicy tissues, as in leaves, herbaceous stems, cortex, 
 tubers of land-plants, and softer kinds of wood, are especially 
 liable to its attacks. In all these cases it first of all decomposes 
 the cellulose into dextrin and glucose by means of a diastatic 
 enzyme which it disengages, and these then undergo the 
 butyric acid-fermentation. Most starch - grains escape its 
 attacks, but paste and soluble starch are very liable to them. 
 Hence the maceration and destruction of parts of plants that 
 are kept wet are to a great extent the work of this Bacillus, 
 alike in cases which involve the economical processes of mankind, 
 such as the maceration and rotting in water of hemp, flax, and 
 
IO2 Lectures on Bacteria. [ ix. 
 
 other textile plants, in order to obtain the fibres, and in such as 
 the wet-rot of bad potatoes according to Reinke and Berthold. 
 Van Tieghem is inclined to attribute to Bacillus Amylobacter a 
 prominent part in the nutrition of ruminant animals, since it 
 vegetates in their stomachs and splits up the cellulose of their 
 food into soluble products of decomposition capable of re- 
 sorption. 
 
 Van Tieghem has also shown or made it probable that this 
 Bacillus has been an active destroyer of cellulose at least since 
 the period of the coal-measures. Fossil plants silicified in a 
 more or less advanced state of maceration, show in their sec- 
 tions the same progression in the destruction of the cell-wall 
 which is observed in macerated plants of the present day, and 
 also the silicified remains of a Bacterium, which he identifies 
 with B. Amylobacter. 
 
 The active powers of fermentation and decomposition of this 
 Bacillus are not confined to the non-nitrogenous bodies just 
 enumerated, as is shown by the investigations of Fitz, which 
 have been before briefly mentioned. The details of these in- 
 vestigations will be found in the works already cited. The 
 behaviour of this Bacillus to proteids will be noticed presently. 
 
 Though there can be no doubt that much the larger number 
 of fermentations producing butyric acid are caused by Bacillus 
 Amylobacter, yet it cannot be said to be the exciting cause of 
 all fermentations which have butyric acid for their primary pro- 
 duct. On the contrary, Fitz describes a large round chain- 
 forming Micrococcus and a short non-endosporous rod-shaped 
 Bacterium, as ferments producing butyric acid in calcium 
 lactate and in some sugars. His former statement, that 
 Bacillus subtilis forms butyric acid by fermentation from starch- 
 paste, and that this fermentation is a very advantageous method 
 of procuring butyric acid, must be founded on a confusion of 
 forms. The typical B. subtilis of Brefeld and Prazmowski can- 
 not be the species intended, for Prazmowski distinctly states that 
 it does not excite fermentation of any kind in starch-paste. 
 
ix.] Decomposition of proteid. 103 
 
 Vandevelde's observation (49) that B. subtilis certainly gives 
 rise to slight fermentation in meat-extract, glycerine, and grape- 
 sugar, after the oxygen is consumed, with special production of 
 butyric acid, can hardly be taken into consideration, for he 
 speaks of very small amounts produced from fermentation, 
 while Fitz states that the amount of butyric acid produced is 
 very large. 
 
 In the absence of more precise morphological observations, 
 the species of the Bacillus subtilis of Fitz's starch-fermentation 
 must for the present remain undetermined. In connection with 
 this question I will here briefly repeat the remark made on 
 page 74, that there are certainly several saprophytic and endo- 
 sporous species of Bacteria, which are very like Bacillus subtilis, 
 and have no doubt been frequently confounded with it. Nothing 
 certain can at present be stated with regard to their effects as 
 ferments. The B. subtilis of Brefeld and Prazmowski, the only 
 form to which I give the name, is clearly distinguished from 
 them by the assemblage of characters described in former lec- 
 tures, and by the mode of germination (page 21), as well as by 
 their collecting on the surface of the nutrient fluid into 
 membranes which are folded in wrinkles, and consist of 
 filaments disposed in parallel zigzags and ultimately forming 
 spores, and by the ellipsoid comparatively broad spores them- 
 selves. 
 
 8. If we examine in conclusion the decompositions which occur 
 in proteid compounds and in glue, we shall first of all see no 
 reason to doubt that all of them, and especially those which are 
 accompanied by the development of gas and are usually known 
 as processes of putrefaction, are the work of Bacteria. The 
 data which we possess show that the processes in these decom- 
 positions and the participation of the different species of Bac- 
 teria in them are, as might be expected, extremely multifarious. 
 The work of distinguishing between the species of Bacteria con- 
 cerned and their specific modes of operation is still in its 
 infancy. 
 
1O4 Lectures on Bacteria. [ ix. 
 
 A point of great importance to notice here is the liquefaction 
 of the gelatine which occurs in cultures of some Bacteria, for 
 example Bacillus subtilis and B. Megaterium, but not in all. 
 
 And here the many-sided Bacillus Amylobacter must again 
 be mentioned. According to the researches of Fitz and Hueppe, 
 this Bacillus decomposes the casein of milk in the following 
 manner : the casein first coagulates as when rennet is employed, 
 the effect being produced by the enzyme disengaged by the 
 Bacillus ; it then becomes liquid and is converted into peptone, 
 and then into further and simpler products of decomposition, 
 among which leucin, tyrosin, and ultimately ammonia, have 
 been ascertained. The fluid meanwhile acquires a more or 
 less pronounced bitter taste. Similar if not identical effects 
 on the casein of milk were observed by Duclaux to pro- 
 ceed from the Bacilli which he names Tyrothrix (see page 52), 
 the greater part of which must also morphologically approach 
 near to B. Amylobacter. Tyrothrix tenuis, for example, first 
 produced the coagulation of rennet, then liquefaction, and after 
 that formation of leucin, tyrosin, ammonium valerianate, and 
 ammonium carbonate. There can be no doubt that these 
 changes, and others connected with them, are the essential part 
 of the phenomena which constitute the process of ripening of 
 the cheese prepared from .the coagulated milk, the above-named 
 Bacteria, with some others, being contained in the cheese, and 
 being procurable from k for the purpose of examination. 
 
 Bienstock (50) has recently submitted the Bacteria of human 
 faeces to careful examination, and found that in those of adults, 
 besides other forms which are unimportant in reference to the 
 processes in question, there is always a particular Bacillus 
 present, which he regards as the specific cause of putrefaction 
 not only of the bodies contained in the faeces, but of those 
 which contain albumin and fibrin. This Bacillus in a pure 
 culture is able of itself to separate albumin or fibrin into the 
 successive products of decomposition which have been ascer- 
 tained in other cases of putrefaction up to the latest and final 
 
fix.] Decomposition of proteid. 105 
 
 products, carbonic acid, water, and ammonia. If allowed to 
 operate on one of the series of decomposition-products already 
 prepared, tyrosin for example, it carries on the decomposition 
 in the order of succession of the regular products of putrefaction. 
 None of the other Bacteria examined by Bienstock produced these 
 effects. Neither casein nor artificially prepared alkaline albumi- 
 nates were rendered putrid by Bienstock's Bacillus; casein is 
 even said to remain entirely unaltered ; in accordance with this 
 the Bacillus itself and the specific decomposition with the 
 characteristic faecal smell are wanting in the intestine of 
 sucking children. 
 
 As regards the morphological characters of this Bacillus of 
 the decomposition of proteid, it appears from the descriptions of 
 Bienstock that it is endosporous, and resembles B. Amylo- 
 bacter in shape at least at the time of formation of spores, and 
 like it forms the motile rods with capitate end (see page 1 7) 
 which Bienstock compares with drumsticks. It is, however, 
 smaller than B. Amylobacter, and even than B. subtilis. It is 
 scarcely possible to form a clear idea of the course of develop- 
 ment of this form from the investigations and descriptions which 
 we possess, and we must wait for further enquiry into this point. 
 
 We must also wait to see whether the monopoly of putre- 
 faction claimed for the drumstick Bacillus will be confirmed. 
 This, with all due acknowledgment of the results as reported, is 
 scarcely probable when we call to mind our experience of other 
 processes of decomposition. I will not bring forward other 
 accounts which have been given as arguments against the ex- 
 clusive character of Bienstock's Bacillus, because precise dis- 
 criminations of form are too recent to set aside the objection, 
 that this Bacillus may be present though unrecognised where 
 some other form is said to have been found, and may be the 
 really active agent. 
 
 But it is necessary, at least, to refer in this place to these 
 other statements, inasmuch as the view pretty generally enter- 
 tained is that Bacterium Termo is the usual exciting cause of 
 
io6 Lectures on Bacteria. [ ix. 
 
 putrefaction. Cohn expresses this opinion in the most decided 
 manner when he says that he has arrived at the conviction, that 
 Bacterium Termo is the ferment of putrefaction in the same 
 sense as beer-yeast is the ferment of alcoholic fermentation, that 
 no putrefaction begins without B. Termo, or proceeds without 
 its multiplication, and that B. Termo is the primary exciting 
 cause of putrefaction, the true saprogenous ferment. Although 
 we cannot now maintain these propositions in their full extent, 
 and although the expression putrefaction is employed in them 
 without any precise determination of the processes of decom- 
 position and of the putrefying substance, yet on the one hand 
 there can be no doubt that the expression includes what is 
 commonly understood by the putrefaction of proteids, such 
 as meat, and on the other hand Bacterium Termo must, 
 at least, be a very constant attendant of such processes. It is 
 advisable, therefore, just to enquire what B. Termo actually is, 
 all the more since modern bacteriology itself scarcely ever uses 
 this old name. There is some ground for this, since it is 
 scarcely possible to make out with certainty what it was that 
 Dujardin, Ehrenberg, and others thirty years ago intended by 
 this name. What Cohn on the contrary described as B. Termo 
 in 1872 is an object as distinct as it is of frequent occurrence. 
 It is obtained by allowing the seeds, for instance, of leguminous 
 plants to rot in water, and then preparing a culture by introduc- 
 ing a drop of the putrid liquid into the solution known as 
 Cohn's nutrient solution for Bacteria 1 . The transference of a 
 drop of the solution thus infected several times in succession to 
 some fresh solution, sufficiently secures the purity of the culture. 
 The microscopic indication of the presence of Bacterium Termo 
 consists in the solution becoming more and more milky during 
 the first days of the culture, and then forming a greenish layer 
 on the surface, in which the form in question is collected in 
 
 1 Cohn's normal solution, as given by Eidam in Cohn's Beitr. i. 3, 
 p. 210, consists of potassium phosphate I gr., magnesium sulphate I gr., 
 neutral ammonium tartrate 2 gr., potassium chloride o-i gr., water, 200 gr. 
 
x.] Bacterium Termo. Parasitic Bacteria. 107 
 
 extraordinary large quantities. Isolation by cultivation in gela- 
 tine is not possible, because the gelatine is at once liquefied by 
 the rapid multiplication of the Bacteria. 
 
 Microscopic examination reveals a number of minute rod-like 
 cells, according to Cohn's measurement about 1-5 /-tin length, 
 and becoming one-half or one-third of that amount in breadth, 
 engaged in active bipartition, and thus frequently united in pairs, 
 but scarcely ever forming long rows; in this they resemble Micro- 
 coccus lacticus, but are distinguished from it by their somewhat 
 larger dimensions, and especially by the very active independent 
 movement of the individuals suspended in the fluid. The move- 
 ment is often a peculiar backward movement in different direc- 
 tions. Zoogloeae are ultimately formed on the surface of 
 the fluid in the form of greenish slimy films or lumps, in 
 which the cells lie motionless. The alternation of these two 
 states was clearly described by Cohn as long ago as 1853. 
 Formation of spores in the characteristic manner has not been 
 observed in B. Termo, and it must therefore be classed for the 
 present with arthrosporous forms. I have said thus much in 
 order to commend the old B. Termo to renewed observation ; 
 time will show how much will be left of it and its reputation as 
 the exciting cause of putrefaction. I leave these sentences as 
 they were originally written, only adding that Hauser has since 
 shown that Cohn's Bacterium Termo is a collective species, and 
 has resolved it into three kinds ; but a closer comparison of 
 these has still to be made (51). I now conclude with it the series 
 of examples of saprophytic Bacteria. 
 
 X. 
 
 Parasitic Bacteria. The phenomena of parasitism. 
 
 WE now pass on to the second category of Bacteria, distin- 
 guished above on page 65 by their parasitic mode of life. 
 
 The term parasite is applied in biology to the living creatures 
 
io8 Lectures on Bacteria. [$ x. 
 
 which take up their abode on or in other living creatures, and 
 feed on the substance of their bodies. The animal or plant 
 which supplies food and lodging to a parasite is termed its 
 host. Parasites are known in very different divisions of the 
 animal and vegetable kingdoms, and many of them are well and 
 certainly understood. I need only mention intestinal worms on 
 the one hand, and on the -other the long series of true Fungi 
 which are parasitic especially on plants. Our experience of 
 these forms, which are comparatively easy to examine, teaches 
 us that the adaptations to the parasitic mode of life are extra- 
 ordinarily complex and present an extreme variety of gradations 
 between one case and another, that is between one species and 
 another, and that these are dependent on the one hand upon 
 the more or less strict requirements of the parasitic mode of 
 life, and on the other upon the mutual relations between parasite 
 and host. 
 
 To attempt to go at all at length into the above relations, 
 would lead us here much too far into details. But we must call 
 attention for our present guidance to one or two of the most 
 important points. 
 
 As regards the nature of the parasitism, we have first the case 
 which is farthest removed from the life of saprophytes, that of 
 obligate parasites, which by the provisions of their nature can 
 only complete the course of their development in the parasitic 
 and not in the saprophytic mode of life. To take an example 
 from amongst those with which we are best acquainted, this is 
 true strictly and excluding all deviation into saprophytism of .the 
 Entozoa, such as tapeworms and Trichinae ; among Fungi, of 
 those which live inside plants and have been termed rusts 
 (Uredineae). These organisms as a matter of fact live only in- 
 side their living hosts and feed on them. It is quite conceivable 
 that the conditions necessary for their development may arise 
 or be artificially produced outside the living host, and it would 
 certainly be an instructive experiment to grow a tapeworm from 
 the ovum in a nutrient solution ; but this has never been actually 
 
x.] Parasitism. 109 
 
 done, and no instance of the kind is to be found in nature. In 
 these cases the parasitism is obligate and indeed strictly obligate. 
 
 I add the word strictly, because there is a modification of 
 obligate parasitism, in which a parasitic mode of life is necessary 
 for the completion of the entire course of the development, and 
 is often the only one which actually occurs, while at the same time 
 saprophytism may take its place, at least in certain stages of the 
 development. No example of this kind occurs to me at this 
 moment from the animal kingdom, but there are some to be 
 found. Among the Fungi there are a number of species of the 
 genus Cordyceps which inhabit insects, especially caterpillars, 
 and in which this adaptation occurs in a marked manner. The 
 germ-tubes developed from spores on the caterpillar penetrate 
 into the insect, spreading luxuriantly in it, and at length killing 
 it, and after its death they fill the whole of its body with mycelial 
 tissue. From this tissue, if the conditions are favourable for 
 vegetation, large Fungus-bodies are produced, several inches in 
 length, which are the stromata of the Fungus, and produce spores 
 (ascospores). These go through the same course of development, 
 if they also find their way to a suitable living insect. But if this 
 does not happen, the spores have the power of germinating on 
 a dead organic substance, for instance in a nutrient solution, 
 and their germ-tubes may develope there into Fungus-plants. 
 But these plants do not produce the characteristic stromata just 
 mentioned. They form different spores from those produced 
 in the stromata, and these spores may also develope in the 
 saprophytic mode of life ; but if they find their way to the 
 proper insect-host, they can recommence the course of develop- 
 ment which reaches its highest point in the formation of stro- 
 mata as described above. Here then we have parasites 
 which are able to complete a certain portion of the course of 
 their development while living as saprophytes, though without 
 reaching its highest point, namely the formation of stromata ; 
 they may be shortly termed facultative saprophytes. 
 
 Thirdly, there are also facultative parasites. These are 
 
no Lectures on Bacteria. [ x. 
 
 species which are able to develope as perfectly, or at least 
 nearly as perfectly, in the saprophytic as in the parasitic mode 
 of life. The ' or ' shows at once that there are gradations also 
 within this category, and these are, as might be expected, 
 of such a kind that some plants find the conditions more favour- 
 able in the parasitic, others in the saprophytic mode of life, 
 while others again show no difference in this respect. There 
 are many instances of these modifications of facultative para- 
 sitism among the Fungi, and we shall soon make acquaintance 
 with similar instances in the Bacteria. 
 
 The mutual relations in each case between parasite and host, 
 the dependence of the one on the other, the benefit or injury 
 which the one receives from the other, are independent of these 
 strict requirements of parasitism which vary in each separate 
 case. In cases like that of the Trichinae, for example, we are in 
 the habit of speaking of this relation as one-sided, as one in 
 which the parasite derives its entire means of subsistence from 
 the living host, while the host receives nothing but harm from 
 the parasite through the necessary withdrawal of its substance 
 and other manifold chemical and mechanical disturbances which 
 it suffers. States of disturbance of the normal existence of a 
 living being, the normal requiring to be determined in each case 
 by experience, are known as diseases ; the parasites of which 
 we are speaking cause these states and are therefore injurious 
 to health, the exciting causes of disease. Further, the parasite 
 by means of its germs, spores, ova, or whatever other name is 
 given to its organs of propagation, may be transferred from the 
 host which has been made ill by it to others in which it will 
 also produce disease. The maladies caused by parasites are 
 therefore transferable from host to host, they are, to use the 
 common expression, infectious. 
 
 But these cases, in which the parasite is injurious to health 
 and the injury is all on one side, are only one extreme among 
 those that are known. There are others in which the two 
 organisms live in common with equal advantage to both, and 
 
x.] Parasitism. 1 1 1 
 
 there is every possible gradation again between these extremes. 
 Lastly, there are cases in which a parasite lives in a host with- 
 out either injuring or sensibly profiting by it, at most deriving 
 its food from the refuse of the metabolism of the host. In 
 extreme cases of this kind, which obviously lie on the border- 
 line of the phenomena of true parasitism, we use the expression 
 lodger-parasites. 
 
 Further, there is a fact more or less known to the experience 
 of every one, which holds good of all the categories of parasites 
 distinguishable according to the points of view here indicated, 
 namely that a parasitic species may make choice as we should 
 say between the hosts which it occupies, that is, attacks one host 
 and thrives perfectly well in or on it, while it either refuses 
 others altogether or at least grows less vigorously in them. In 
 these respects also there is every conceivable gradation. First, 
 as regards the choice of the host-species by a parasitic species ; 
 one extreme is marked by the narrowest one-sidedness. For 
 instance, a strictly obligate and very well marked parasitic 
 Fungus, Laboulbenia Muscae, mentioned on page 39, grows 
 exclusively on the house-fly and on no other insect, at least 
 according to our present investigations. Other Fungi and 
 other parasites besides the Fungi are not so one-sided in their 
 choice, since they attack a larger number of host-species, but 
 those only as a rule which belong to a narrow cycle of affinity, 
 a genus, family, &c. Thus, for example, some of the species of 
 Cordyceps mentioned above, grow in the larvae of a great 
 variety of butterflies and other insects. But it sometimes 
 happens that single host-species within such a cycle of affinity 
 remain excluded from the choice for reasons of which we are 
 ignorant. Lastly, we are acquainted with obligate and faculta- 
 tive parasites which are able to complete their development 
 equally well in hosts of the most different cycles of affinity. 
 I need only mention Trichina spiralis once more, which thrives 
 well in rodents, swine, men, and other animals. Examples in 
 plenty may also be drawn from the Fungi ; but among them 
 
H2 Lectures on Bacteria. [f x. 
 
 also strange exceptions occur within a cycle of preference, some 
 host-species being spared by the parasites without any definable 
 reason. To name only one instance, a Fungus named Phyto- 
 phthora omnivora from its catholicity of taste attacks the most 
 heterogeneous plants, species of Oenothera and other herbs and 
 garden-flowers, Sempervivum, the beech, &c. ; on the other 
 hand it never attacks the potato-plant, which its nearest relative 
 Phytophthora infestans prefers. 
 
 It is at present scarcely possible to give an exact account of 
 the physiological causes of these preferences, but it is at the 
 same time obvious that they depend essentially on chemical and 
 physical qualities and distinctions. 
 
 If then there is a choice between one species and another, 
 there must be a similar choice to a certain extent between indi- 
 viduals of the species, for the differences between the several 
 species are the same in kind, though not in degree, as those 
 between individuals of one and the same species ; the latter are 
 less than the former, and are therefore also less pronounced, 
 being sometimes scarcely or not at all perceivable ; gradations 
 between the different cases which we meet with everywhere are 
 also not wanting here. 
 
 If we describe these phenomena which run through the whole 
 of the long series of parasites in the reverse way, that is to say, 
 not with reference to the parasite but to the host, then we say 
 that the host is differently suited, disposed, or predisposed, ac- 
 cording to the species and individual for the attack of a parasite. 
 We may speak of predisposition on the part of a species, or 
 individual, or in different states, stages of development, or ages 
 of an individual. Of these individual predispositions it may be 
 further specially observed that they must, no less than all others, 
 as a general rule, have their foundation in each case in the 
 chemical, physical, and anatomical constitution. It may be 
 shown for example in the case of certain Fungi of the genera 
 Pythium, Sclerotinia, and others which live in plants, that indi- 
 viduals of the same host-species have unequal susceptibility to 
 
} x.] Parasitism. 113 
 
 the attacks of the parasite, and unequal power of resisting them 
 according to the relative amount of water which they contain. 
 Since in these cases youngerplants have more water than the older, 
 a predisposition dependent on age is also indicated accordingly. 
 
 In cases where the parasite causes a disturbance, which we call 
 sickness, of what by experience is regarded as the normal vege- 
 tation of the host, if the predisposition is individual we speak 
 usually of a sickly predisposition. This may be correct, in 
 so far as the predisposition to the attack of the parasite may 
 be connected with deviations from the state which is from ex- 
 perience termed the sound state. But it need not always be 
 correct, for there is no reason at all why the disposition for the 
 attack of the parasite should in every case indicate a condition, 
 which must be called sickly even when there is no parasite 
 present. The above-mentioned example of the predisposition 
 varying with the age is a sufficient proof of this. Here we must 
 distinguish between one case and another, and care is required 
 in determining each individual case. 
 
 An example may help to make this still more plain ; it is that 
 of a case which is comparatively very accurately known. The 
 common garden-cress, Lepidium sativum, is often attacked by 
 a parasitic Fungus of comparatively large size, Cystopus can- 
 didus. In consequence of this it shows considerable degene- 
 ration, swellings, curvatures of the stem, and often also of the 
 fruits, and on these parts and on the leaves white spots and 
 pustules subsequently turning to dust, which are formed by the 
 sporogenous organs of the Cystopus, and give the entire phe- 
 nomenon the name of the white rust in cress. This is a case of 
 disease, and so striking that every one notices it at once with the 
 naked eye. Now we find in a bed of cress at about flowering 
 time a certain number of rusty plants, two for example or 
 twenty. They are in the middle of the other hundred or 
 thousand plants, and these are healthy and free from the Fungus 
 and continue so till the period of vegetation is at an end. This 
 is the case, though the Cystopus forms countless spores in the 
 
 i 
 
H4 Lectures on Bacteria. [ x. 
 
 white rust-pustules, and the spores are dispersed as dust and 
 are at once capable of germination, finding the necessary con- 
 ditions for their further development in the bed of cress, and 
 are the instruments by which the white rust-disease is emi- 
 nently infectious. Nevertheless those hundred or thousand 
 plants are not infected. All that has been hitherto said is strictly 
 correct, and if we limit our view to this, we shall see in the 
 phenomena which have been described a conspicuous case of 
 individual difference in predisposition; a case too perhaps, if 
 we judge hastily, of sickly predisposition in the plants attacked, 
 for they do become sick and the others do not. And yet 
 this is not the true account of the matter. Every healthy 
 cress-plant is equally liable to the attacks of the Cystopus and 
 to the rust-disease which it causes, only the liability is confined 
 to a certain stage of the development, and ceases once for all 
 when that stage is past. The germinating cress-plant in effect, 
 first unfolds two small three-lobed leaves, the seed-leaves or 
 cotyledons. When it has grown a little further and formed 
 more foliage-leaves, the cotyledons wither and drop off. It 
 appears then, that the germ-tubes of the Fungus of white rust find 
 their way into all the cotyledons and are able to develope there, 
 and if this development has once begun, the Fungus establishes 
 itself at once in the tissue into which it has penetrated, and 
 grows on in and with the growing plant, and produces the 
 disease. The germ-tubes of Cystopus may indeed make their 
 way for a short distance into all the other parts of the plant, but 
 are unable to establish themselves inside it and continue their 
 development. The plant is for the future safe from the attacks 
 of the parasite as soon as the cotyledons have fallen off. The 
 two or the twenty rusted plants in the bed are the ones in which 
 the Fungus attacked the cotyledons in good time; if it had 
 attacked the thousand others in equally good time, all would 
 have been rusted. They continued healthy, because they were 
 not infected in the stage in which they were open to infection, 
 that is, predisposed. 
 
XL] Harmless Parasites. 115 
 
 It follows necessarily from what has been said with respect to 
 the variety of gradations in the mutual relations of host and 
 parasite, that the progress and issue of the disease must also 
 show manifold gradations, varying with the species on both 
 sides, and in a less degree with the individuals. The very 
 general occurrence of Trichinae, tapeworms, the itch and other 
 diseases bring them so much under the notice of all, that this 
 brief notice of them here will be sufficient. 
 
 XI. 
 
 Harmless parasites of warm-blooded animals. Parasites 
 of the intestinal canal. Sarcina. Leptothrix, Micro- 
 cocci, Spirillum, Comma -bacillus of the mucous 
 membrane of the mouth. 
 
 IT seemed to me expedient to give the foregoing short review 
 of the phenomena of parasitism and of its consequences, because 
 all that we know of parasitic Bacteria are only special cases of 
 the main phenomena which occur everywhere ; and this is 
 equally true of all our suppositions concerning them. The 
 understanding of these matters will therefore be materially aided 
 by resting on old and long-known phenomena. 
 
 In passing now to the consideration of important examples 
 of parasitic Bacteria, it will be advisable to speak first and 
 chiefly of the parasites of warm-blooded animals, including 
 mankind, and afterwards to say a few words on those of other 
 animals, and of plants. 
 
 In the former class it will best suit our purpose to distinguish 
 the species which are the exciting causes of disease from those 
 which are less injurious or altogether harmless ; and first a few 
 words respecting the latter kind. 
 
 The digestive canal and the breathing passages, the former 
 especially, are a favourite habitat of lower organisms, Fungi and 
 Bacteria, putting the various kinds of worms out of considera- 
 tion. A large number of Fungi make use of the intestinal canal 
 
 I 2 
 
Ii6 Lectures on Bacteria. [$ xi. 
 
 as a regular, if not in most cases an absolutely indispensable 
 thoroughfare, since when introduced with the food they find a 
 home and nourishment in it for the first stages of their develop- 
 ment, and then complete it on the voided faeces. This is shown 
 by the abundant and remarkable Fungus-flora of dung. 
 
 It is known that many forms of Bacteria occur in large 
 numbers in the contents of the intestinal canal. A more 
 thorough sifting and sorting of most of the species has yet to be 
 undertaken. In the human intestine Nothnagel has distinguished 
 Bacillus subtilis, B. Amylobacter, and other not clearly defined 
 forms, and Bienstock (50) his drum-stick Bacillus. Kurth found 
 his Bacterium Zopfii in the intestine of fowls (see page 22). To 
 these examples must be added the constant, and according to 
 van Tieghem (see page 102), the essential presence of Bacillus 
 Amylobacter in the stomachs of ruminants (52). 
 
 The acid of the gastric juice may prevent the appearance of 
 most of the Bacteria in the normal contents of the stomach (in 
 the rennet-stomach in ruminants). Koch's researches into 
 anthrax, to be noticed again presently, have even shown that 
 Bacillus Anthracis in the vegetative states is killed by the gastric 
 juice, and only its spores maintain their vitality. This may be 
 the case with some other species, and it may be of some import- 
 ance that a kind of sorting thus takes place in the normal 
 stomach, by means of which some only of the Bacteria intro- 
 duced with the food reach the intestinal canal in the living state. 
 
 That the gastric juice has not always an injurious effect, but 
 that here too there is a difference between one case and another, 
 is shown by the researches of Miller and W. de Bary (52). We 
 are acquainted with one species, the well-known Sarcina ven- 
 triculi (Fig. 14), which thrives particularly well in the human 
 stomach. This species forms packets in the shape of almost 
 perfect cubes of roundish cells arranged in regular layers 
 parallel with the surfaces of the cube, and kept firmly united by 
 tough gelatinous membranes. Comparison shows plainly that 
 the packets are formed in the manner which can be directly 
 
XL] Sarcina. 117 
 
 observed in the case of other very similar species (see Fig. 15), 
 namely, from a single round initial cell by successive divisions 
 formed in three directions. The packets separate as they 
 grow into daughter-packets, each of which contains the progeny 
 of one of the cells of previous orders of division, and as this pro- 
 cess is repeated the packets multiply. Nothing further is known 
 of the history of the development of Sarcina. 
 
 Sarcina ventriculi is at present known only from the human 
 stomach and intestinal canal. In diseases, especially enlarge- 
 ments, of the stomach, it is often found in incredible quantities. 
 
 /ffl 
 
 a Z c d 
 
 Fig. 14. Fig. 15. 
 
 Yet no causal connection has been ascertained between its 
 occurrence and distinct phenomena of disease, and other con- 
 ditions being the same it may be present in profusion or 
 sparingly, or be absent ; its absence indeed is the rule in much 
 the larger number of stomachs, diseased as well as healthy. The 
 causes of all this are unknown ; nor can we tell whence it finds 
 its way into the stomach. Its occurrence outside the stomach 
 
 Fig. 14. Sarcina ventriculi, Goodsir. Large-celled form just taken from 
 the contents of the stomach of a patient and imbedded in soft gelatine ; a 
 comparatively small and cube-shaped packet. View of one surface only ; but 
 other surfaces project below and to the right beyond the edge of the first. 
 In the surface depicted the cells with double contour-lines are rightly 
 focussed ; those with single contour- lines are not in the right focus but lying 
 at a lower level. Magn. 600 times. 
 
 Fig. 15. Sarcina minuta, de Bary, in gelatine on a microscopic slide. 
 a-d successive states of the same specimen, observed as a double pair of 
 round cells, a about 4, b about 6, c about 9, and d at 10 o'clock in the 
 afternoon. In c the tetrads are still formed of a single layer, in d a division 
 has taken place in each cell in the plane of the paper ; each tetrad de- 
 velopes into an 8-celled cube-shaped packet, /a 32-celled pocket. See 
 note 53. 
 
1 1 8 Lectures on Bacteria. [$ xi. 
 
 and intestine, excepting of course in the evacuations, has not 
 been observed with any certainty, and the attempts to cultivate 
 it have, up to the present time, been without success in all cases 
 offering clear results. 
 
 It is true that we are acquainted with a number of forms or 
 species, in which the cubical packets are so like those of Sarcina 
 ventriculi that they must be placed alongside of it as closely 
 allied forms. These occur both outside living organisms, as 
 saprophytes, and also in the bodies of living animals, and 
 among them of men. That they are not very widely diffused 
 is evident from the fact that the reported cases of their occur- 
 rence are always solitary ones. 
 
 Saprophytic forms of Sarcina have been found casually, that 
 is without having been introduced intentionally, by Cohn and 
 Pasteur on all kinds of nutrient solutions, by Schroter on boiled 
 potatoes, by myself on acetified beer, on coagulated milk, and 
 elsewhere. In these instances the yellow forms (Sarcina lutea, 
 S. flava) have repeatedly been observed (53). 
 
 Sarcina-forms inhabiting the bodies of living animals are 
 described as obtained from the bladder (S. Welckeri), the lung, 
 the mouth, and other cavities of the body, even from the blood 
 of the human subject, and from the cavities and the intestinal 
 canal of other warm-blooded animals. 
 
 These forms, the saprophytic as well as the parasitic, are, so 
 far as the statements before us enable us to judge, without 
 doubt clearly distinct from Sarcina ventriculi. Unfortunately 
 many accounts are so defective, so very much restricted, one 
 might say, to the word Sarcina, that it is impossible to determine 
 their identity. The fact moreover which was noticed in the 
 case of Sarcina ventriculi is also true of the parasitic forms ; 
 their occurrence, as far as our knowledge goes, has not been 
 shown to be in causal connection with distinctly morbid pheno- 
 mena, and they must for the present be regarded as simply 
 lodger-parasites (53). 
 
 Many kinds of Bacteria are observed in the mucous mem- 
 
XL] Bacteria of mucous membrane of mouth. 119 
 
 brane of the mouth and nose. With regard to the latter this 
 assertion favours the supposition that Bacteria are uniformly 
 present in that catarrh of early summer which goes by the 
 name of hay-fever. I can bear out this statement myself 
 as a sufferer from this disagreeable malady, though I must 
 add that Bacteria are also present during the 10-11 months 
 of the year that are free from hay-fever. I found them to 
 be small, short rods resembling those of Bacterium Termo. 
 Whether specifically different forms are present, or predominate 
 at different times, has not been ascertained. 
 
 We are better acquainted with the abundant growth of Bac- 
 teria in the mucous membrane of the mouth. They occur in 
 greatest profusion on the gums and 
 between and on the teeth, in a more 
 scattered manner, but still in con- 
 siderable numbers on the rest of 
 the surface of the mouth and in the 
 discharged saliva. A specimen of 
 mucus scraped from a tooth is seen e 
 to be chiefly composed of a form 
 known by the old name of Lep- 
 tothrix buccalis, Robin (Fig. 1 6, a). 
 It consists of long straight filaments 
 glued together into dense bundles, 
 brittle and readily separating into 
 
 Fig. 1 6. 
 
 pieces transversely, and of unequal thickness ; larger filaments 
 
 Fig. 1 6. Bacteria from mucus of the teeth, a Leptothrix buccalis, Robin ; 
 filaments or portions of filaments of different thickness, b a portion of a 
 filament after treatment with alcoholic solution of iodine showing the 
 segmentation distinctly, c portion of a filament much narrowed at one 
 end, without treatment with reagents and showing segmentation distinctly. 
 d Lewis' comma-bacillus, that is, a short-celled Spirillum, e Spirochaete 
 Cohnii, Winter (Spirochaete of mucus of the teeth, Cohn, Beitr. i. 2, p. 180, 
 and ii. p. 421). m Micrococcus-heaps. All the figures are of specimens from 
 the same preparation, e and b after staining, the rest fresh from the mouth. 
 Magn. 600 times, with the exception of <$, which is more highly magnified. 
 
1 20 Lectures on Bacteria. [$ xi. 
 
 are over i fi in the transverse diameter, others only half that 
 thickness. The length also of the members (cells) is unequal, 
 in some cases not exceeding the transverse diameter, in others 
 several times greater. The filaments, especially those with 
 short and thick cells, often show the reaction of granulose 
 (page 5), but different portions of the same filament may assume 
 alternately a blue and yellow colour with iodine. Rasmussen 
 (54) claims to have distinguished three separate forms of Lep- 
 tothrix buccalis by aid of cultivation. I cannot say whether 
 this is rightly done or not, for Rasmussen's work is only known 
 to me at second hand. 
 
 Secondly, the masses of Leptothrix often contain round Cocci, 
 which are sometimes irregularly rolled up into dense gelatinous 
 heaps, and like the Leptothrix-forms are without the power of 
 motion (Fig. 1 6, m). 
 
 Thirdly, a Spirillum-form is commonly found with the others, 
 showing itself rather in single specimens and in the fluid sur- 
 rounding the Leptothrix-masses after addition of water ; this is 
 Spirochaete Cohnii, Winter (S. buccalis or S. dentium), and 
 consists of filaments of extreme tenuity without evident trans- 
 verse divisions, spirally twisted into 3-6 or more steep 
 and often irregular coils, flexible and either exhibiting a slow 
 twisting movement or else without motion (Fig. 16, e). 
 
 Lastly, one more form is often though not always observed 
 with the others, a thin short rod-shaped Bacterium, bent like 
 a bow, and described first by Miller and then by Lewis (55) 
 as the comma-bacillus of the mucus of the mouth (Fig. 16, </); 
 in a fluid it usually exhibits an active hopping movement. 
 
 It may be assumed beforehand as certain, that besides these 
 forms other saprophytic Bacteria must also occur in the mucus 
 of the mouth. Miller, according to recent communications, has 
 found twenty-five such organisms. Hueppe speaks of two 
 Micrococci which produce lactic acid as coming from the human 
 mouth (see page 94). But other forms do not appear to be 
 developed in any abundance in healthy individuals. It may be 
 
XL] Bacteria of tooth-caries. 121 
 
 said perhaps that their invasion is hindered by the presence 
 of the characteristic dwellers in the mouth mentioned above. 
 
 I repeat that I would have these latter spoken of at present 
 only as forms which are actually present side by side, nor will 
 I enter further into the question how far they stand in genetic 
 relation to one another. From the impression which they give 
 us and from present investigations it seems to be highly probable 
 that we have before us several distinct social species. 
 
 The dwellers in the digestive and respiratory passages which 
 have now been described, together with other near allies found 
 in mammals are, so far as our knowledge goes, almost without 
 exception harmless guests, lodger-parasites only, those which 
 live in the mouth being perhaps even useful as protectors 
 against an invasion of destructive ferment-forms. Certain forms 
 however are disagreeable exceptions, inasmuch as they cause 
 caries, the disease in which the teeth become hollow. Every 
 hollow tooth is penetrated throughout by Bacteria, and different 
 forms or species occur in different cases ; Miller (55), after ex- 
 amining hundreds of teeth, has distinguished five of these forms. 
 He has also shown by very thorough investigation that one of 
 them, a Micrococcus, forms lactic acid in a substratum contain- 
 ing sugar or starch. The salts of calcium in the substance of 
 the tooth are dissolved by the excreted acid, and the Bacterium 
 is thus enabled to force its way into the tooth ; as more and 
 more of the calcium is withdrawn the Bacterium passes into 
 the tubuli of the dentine of the tooth, and ultimately spreads 
 through and destroys the tooth. It can scarcely be doubted 
 that Miller's/our other species produce the same effects. 
 
122 Lectures on Bacteria. [ xn. 
 
 XII. 
 Anthrax and Fowl-cholera. 
 
 LEPTOTHRIX buccalis, as the exciting cause of caries in the 
 teeth, carries us on to those parasites in warm-blooded animals 
 which produce disease. 
 
 The best way to obtain a clear idea of these organisms, their 
 manner of life, and their effects will be to examine first of all 
 some comparatively well-known examples. 
 
 Let us take first the disease known as anthrax, charbon, sang 
 de rate and its exciting cause, Bacillus Anthracis (56). 
 
 Bacillus Anthracis has already been repeatedly brought be- 
 fore our notice. Its description will therefore only be briefly 
 recapitulated here, and its figure reproduced (Figs. 17, 18). It 
 consists of cylindrical cells about 1-1-5 /u ^ n thickness, and 3-4 
 times that length. In the blood of animals these cells are usually 
 connected together into long straight rods (Fig. 17, c), which 
 appear homogeneous till they are carefully examined, that is, do 
 not distinctly show segmentation into individual members. When 
 grown in a dead substratum the rods develope into very long 
 filaments, which appear sharply bent in several places, and form 
 curvatures and loops ; they also separate at the points of flexure 
 into rod-shaped pieces, and are usually collected in large numbers 
 into bundles or sheaves and twisted round one another (Fig. 1 7, a). 
 The rods and filaments are without the power of locomotion, 
 except in special cases, which will be noticed below. The 
 formation and germination of the spores take place in the 
 manner described in Lecture III in the case of the endosporous 
 Bacilli; in germination the spores merely grow in length 
 (Fig. 1 7, b} without throwing off any distinct spore-membrane, 
 and the young germ-rod often exhibits a slow oscillating move- 
 ment. The ripe spore is broadly ellipsoidal, as broad as its 
 mother-cell which retains its cylindrical shape but much shorter, 
 and lies very nearly in the middle of the mother-cell till it is 
 set at liberty by the swelling of the membrane. 
 
XII.] 
 
 Anthrax. 
 
 123 
 
 Bacillus Anthracis is distinguished under the microscope by 
 the absence of independent motion and by the form of its ger- 
 mination from B. subtilis, which is very much like it in almost 
 all respects, except that it is usually more slender and is not 
 parasitic. To these must be added in 
 ordinary cases the macroscopic dis- 
 tinction, that B. Anthracis at the 
 highest point of its development forms 
 a floccose sediment in nutrient solu- 
 tions, while B. subtilis forms the dry 
 membrane on the surface mentioned 
 on page 12. Some exceptional phe- 
 nomena will be noticed further on. 
 
 Anthrax chiefly attacks mammals, 
 and among these the most liable to 
 it are herbivorous animals, especially 
 rodents and ruminants ; of the species 
 which have been observed, domestic 
 mice, guinea-pigs, rabbits, sheep, and 
 horned cattle are the most susceptible 
 in the order of naming. The next in 
 the degree of liability are omnivorous 
 animals, and among them men ; then 
 come the carnivores, and among these cats, for instance, are 
 more frequently attacked than dogs. Birds also are said to be 
 susceptible to the disease, though this has been disputed ; Gibier 
 found that frogs, and Metschnikoff that lizards (Lacerta viridis) 
 were susceptible when they were kept at about the temperature 
 of the bodies of warm-blooded animals. We will pass over 
 
 Fig. 17. Bacillus Anthracis. a portion of a group of vigorously growing 
 filaments ; the segmentation into cells is not visible, but has nevertheless 
 taken place, b three successive stages of a germinating spore ; close by is 
 a ripe spore s before germination, c rod from the blood of an infected 
 guinea-pig some hours after the death of the animal, after treatment with 
 distilled water, a and b from cultures on microscope-slides in solution of 
 extract of meat. Magn. 600-700 times. 
 
 Fig. 1 7. 
 
124 
 
 Lectures on Bacteria. 
 
 [I xii. 
 
 f 
 
 2 
 
 disputed points on the present occasion, leaving them to be 
 examined in the special literature of the subject (56), and con- 
 fine ourselves to cases which have been 
 certainly ascertained, especially those in 
 mammals. Susceptibility to infection varies 
 with the species, as appears from what 
 has been already said ; within the limits 
 of the species it varies according to race 
 and age, and with the individual. 
 
 Anthrax is a widely-spread form of 
 disease; at the same time it is matter of 
 long experience, that it appears with un- 
 usual frequency in certain districts, and 
 that these anthrax-districts are especially 
 dangerous to herds of cattle, and are there- 
 fore dreaded by breeders. 
 
 The clinical aspect of the disease is 
 different in different species of animals ; 
 in larger ones it is said to run a com- 
 paratively slow course, being accompanied 
 with violent fever, &c., and in most cases 
 but not always ends in death. Mice and 
 guinea-pigs succumbed to the disease 
 almost without exception in the cases ob- 
 served, but without showing any particularly striking symptoms 
 
 Fig. 1 8. 
 
 Fig. 1 8. A Bacillus Anthracis. Two filaments partly in an advanced stage 
 of spore-formation ; above them two ripe spores escaped from the cells. From 
 a culture on a microscope-slide in a solution of meat-extract. The spores 
 are drawn a little too narrow ; they are nearly as broad as the breadth of 
 the mother-cell. B Bacillus subtilis. 1 fragments of filaments with ripe 
 spores. 2 commencement of germination of spore ; the outer wall torn trans- 
 versely. 3 young rod projecting from the spore in the usual transverse 
 position. 4 germ-rods bent into the shape of a horse-shoe, one subsequently 
 with one extremity released. 5 germ-rods already grown to a considerable 
 size, but with both extremities still fixed in the spore membrane. All 
 magn. 600 times. 
 
xii.] Anthrax. 125 
 
 up to the moment of death. In many instances I observed 
 guinea-pigs lively and eager for food, till they all at once (about 
 forty-eight hours after infection) collapsed and died after a short 
 struggle. 
 
 If a diseased animal is examined a little before or immediately 
 after death, the vegetative rods of Bacillus Anthracis (Fig. 17, c) 
 are found in its blood. In larger animals, such as horned 
 cattle, their numbers appear from the accounts before us to vary 
 in every case. I say appear for reasons to be given presently. 
 But they are always found in the capillaries of the internal 
 organs, at least in the spleen. Koch states that they are not 
 numerous in the blood of rabbits and mice, but are all the more 
 numerous in the lymphatic glands and in the spleen. In guinea- 
 pigs, the animals which I have myself chiefly examined, the 
 entire mass of the blood is permeated by the rods ; the smallest 
 drop of blood, scarcely visible to the naked eye, taken from a 
 slight puncture in the ear, or toe, or elsewhere, contains them ; 
 they are present in enormous numbers in the small vessels and 
 capillaries of the liver, kidneys, spleen, and other organs. The 
 same state of things continues for some time also after death ; 
 at a later period, when the first rigidity of death is passed away 
 it often changes visibly, and it is possible to obtain considerable 
 quantities of blood from the large blood-vessels, or from the 
 heart of the animal without discovering a single rod in them. 
 The rods are there but they are inclosed, often in large numbers, 
 in the clots of fibrin, which it may be said in passing will supply 
 the purest material for the culture of the Bacillus. It is quite 
 possible that in the cases in which few rods were observed, the 
 reason was, that those which were inclosed in the clots of fibrin 
 were overlooked when the dead animal was examined after the 
 coagulation of the blood ; this is a point to be remembered in 
 connection with the statements mentioned above, that the Bacilli 
 are present sometimes in larger sometimes in smaller quantities. 
 
 The rods were first seen by Rayer in 1850, and next by 
 Pollender, independently of Rayer, in 1855. The causal con- 
 
126 Lectures on Bacteria. [ xn. 
 
 nection between the Bacillus to which the rods belong and the 
 disease known as anthrax was first distinctly pointed out by 
 Davaine in 1863, and this view of the matter, though it has been 
 opposed on various grounds, is now accepted. It has been 
 distinctly proved that the disease makes its appearance only 
 when the Bacillus has found its way into the blood, and that the 
 artificial introduction of the Bacillus into the blood results in 
 the characteristic infection, the sickening of the animal. The 
 infection follows if the living Bacillus is introduced directly 
 into the blood by intentional inoculation, anthrax by inocula- 
 tion, or unintentionally through wounds of the skin, anthrax 
 by wounds, or through the uninjured mucous membrane of the 
 intestinal canal, intestinal anthrax. It is effected both by means 
 of living rods, and by spores, the latter then germinating in 
 the blood or in the intestine. In both cases it is a matter 
 of indifference whether the matter used for infection is obtained 
 direct from a diseased animal or from a culture, such as will 
 be described presently, which has been kept free from every 
 trace of any product of animal disease. The Bacillus, when 
 it has died of itself or been killed, is incapable of producing 
 the infection. 
 
 When once the Bacillus has found its way into the blood of 
 an animal capable of the infection, it grows and multiplies in the 
 rod-form and spreads partly by its own growth, partly by the 
 movement of the blood which carries the rods along with it in 
 the manner described above. In proportion as this takes place, 
 the sickness increases till at length death supervenes. The 
 minutest possible quantity of the living Bacillus is sufficient to 
 set these processes going. A guinea-pig, for example, dies with 
 the symptoms which have been described in forty-eight hours 
 after a quantity of spores or rods, too small to be visible with a 
 pocket-lense, is introduced into the skin on the point of a needle 
 by a puncture too slight to draw blood. 
 
 Anthrax by inoculation and anthrax by a wound are alike 
 caused by the introduction of both spores and living rods. 
 
$ xii.] Anthrax. 127 
 
 Intestinal anthrax on the contrary is actually produced only 
 by the introduction of spores into the body, as has been proved 
 by Koch and his colleagues. In the natural course of things 
 the Bacillus can only reach the mucous membrane of the 
 intestine from the mouth, that is, when it is swallowed with 
 food. It has then to pass through the stomach, and here the rods 
 lose their efficiency, doubtless from the effects of the acid gastric 
 juice ; whether they are actually killed by it I am not prepared 
 to say. The spores, on the contrary, pass unaltered through 
 the stomach ; they find the conditions favourable to germination 
 in the contents of the intestine, and the rods developed in 
 germination make their way into the mucous membrane of 
 the intestine, especially through the lymph-follicles and Peyer's 
 patches; from there the way is open through the capillary 
 vessels in the mucous membrane to the passages of the 
 blood. 
 
 It appears from the investigations of the above-named ob- 
 servers that animals which chew the cud are liable to be infected 
 in this way from the intestine. The experiments were made 
 with sheep. Experience also with horned cattle not purposely 
 infected seems to show by its agreement with these experiments 
 that the latter animals also are liable to this mode of infection. 
 It gives also the important practical result, that the cases of 
 anthrax which occur in them spontaneously, that is not inten- 
 tionally produced for experiments' sake, are chiefly of the 
 intestinal form, and are caused therefore by taking in the spores 
 of the Bacillus with the food. 
 
 Other animals are less susceptible of infection from the intes- 
 tine; yet some attempts made to procure it succeeded in the 
 case of guinea-pigs, rabbits, and mice ; they were all unsuccessful 
 with rats, fowls, and pigeons. 
 
 After all these experiences the first question is, whence do 
 the spores come from which enter the animal ? They are not 
 formed either in the living animal or in the unopened carcase, 
 for there vegetative development only takes place. But it was 
 
128 Lectures on Bacteria. [$ xn. 
 
 shown in a former Lecture that the Bacillus can not only 
 germinate and vegetate luxuriantly outside the body of the 
 animal, but that it forms its spores, in great profusion if the 
 conditions are favourable, only outside the animal. The con- 
 ditions for this non-parasitic development are the same as the 
 general conditions given above for saprophytes. A supply of 
 oxygen is required for perfect development ; the optimum tem- 
 perature for the formation of spores is 20-25 C. A great variety 
 of organic bodies can serve as nutrient material, as experiments 
 show, not only such as are of animal origin, for instance, por- 
 tions of an animal that has died of anthrax, or the often bloody 
 evacuations of diseased animals, or the meat-extract-solution in 
 which the culture of the Bacillus was first accomplished (see 
 page 12), but also many different parts of plants if they are not too 
 acid, such as potatoes, turnips, seeds, &c. On the moist surface 
 of such objects the Bacillus grows and forms extensive mem- 
 branous coverings, which at the close of their vegetation produce 
 countless spores. 
 
 Thus it is evident that the Bacillus of anthrax belongs to the 
 class of facultative parasites, as described on pages 109,110. It is 
 above all a saprophyte, for it is not only able to prolong its exist- 
 ence in the saprophytic mode of life, but it requires it in order to 
 attain to the highest phase of its development, the formation of 
 spores. On the other hand it is capable of parasitism, since it 
 finds its way into the proper host, and there acts as the exciting 
 cause of disease in the manner which has just been described. 
 
 The phenomena attending the appearance of anthrax are now 
 completely explained in all essential points from the mode of 
 life of the Bacillus, if we take its existence for granted in the 
 same sense as that of any other animal or vegetable species. 
 The fact that anthrax when spontaneous usually appears in the 
 intestinal form, shows according to the knowledge which we 
 have acquired of it, that it passes in the spore-form from the 
 saprophytic into the parasitic state, and that the route which it 
 takes must be the same as that which serves for the food taken 
 
XIL] Anthrax. 129 
 
 in by the animal. The starting-points in this migration must 
 then be the places where the fodder is produced, meadows, 
 grazing-grounds, &c. It is obvious that the Bacillus finds 
 opportunity for its vegetation, and in the heat of the summer 
 season the requisite temperature for forming its spores, on the 
 dead organic bodies which are always to be found in these 
 localities, and that when it has once established itself it can pass 
 the winter there (see above, page 51), and thus remain from year 
 to year in readiness to establish itself in a suitable host. 
 
 It is more difficult to say precisely why certain localities 
 are the favourite homes of anthrax whilst others are free from 
 it. Koch has shown some ground for thinking that the 
 preference may be connected with conditions of moisture and 
 inundation, so far as these affect the vegetation and diffusion 
 of the Bacillus. I have not the requisite material for forming 
 a decided opinion. It follows from what has been before said 
 that the Bacillus is not obliged to return from its existence 
 as a parasite and from the body of the attacked or dead 
 animal to saprophytic vegetation in the infected places ; as it is 
 not obliged to pass through the state of parasitism, it can, as we 
 learn from cultures, live as a saprophyte through an unlimited 
 number of generations. On the other hand experience as cer- 
 tainly shows that it can return from the sick or dead animal to 
 the life of saprophytism, for it remains in the animal long after 
 its death and continues alive and capable of growth, and it can 
 in fact return to the ground and to the condition of a sapro- 
 phyte with the bloody .dejecta, which, as we are told, larger 
 animals void in a severe attack of anthrax, or with the decom- 
 posing carcases and the substances flowing out therefrom, which 
 are excellent food for them. 
 
 The Bacillus can at the same time also be transported as a 
 parasite from one place to another, and the spots on which sick 
 animals fall down or their dead bodies are buried may become 
 the abodes of the disease, as experience has long since shown. 
 For the same reason a locality may possibly continue perma- 
 
 K 
 
130 Lectures on Bacteria. [ xn. 
 
 nently infected. If no herds of cattle visit them, small animals, 
 the rodents especially, which are so susceptible of the disease, 
 may ensure the introduction and conservation of the Bacilli. 
 But these circumstances are, as was said, not directly necessary 
 for the existence of the Bacillus and of the risk of anthrax, not- 
 withstanding the importance which has been attributed to some 
 of the conditions connected with them. 
 
 To complete this review of the subject we may remark in 
 conclusion, that the Bacillus and its effects appear to be trans- 
 ferable as might be expected from one living animal to another, 
 and the disease is propagated by this transmission. This infec- 
 tion belongs of course to the category above distinguished, of 
 anthrax as produced by inoculation or by a wound. It can 
 only be brought about by means of vegetating rods, because 
 these alone are present in the living animal, and the rods, as we 
 saw, must be conveyed directly into the blood of the living 
 animal, to be capable of further development. And now the 
 conditions of infection have been sufficiently indicated for 
 our purpose. A possibly exaggerated importance has been 
 ascribed to stinging flies and gnats as agents of infection, 
 since these insects, when they have sucked blood from an 
 animal which contains Bacilli and then puncture a healthy 
 animal for the same purpose, may easily effect a true inoculation 
 of the disease. 
 
 The Bacillus of anthrax in the character of a parasite pro- 
 duces in the animals and in the cases which have been described 
 injurious effects, which may be provisionally compared to those 
 of a poison, and may therefore be termed poisonous and 
 virulent. 
 
 This virulence may be gradually attenuated till it ceases to be 
 dangerous even in the case of that most susceptible of all the 
 animals experimented on, the domestic mouse. Pasteur has 
 shown that this takes place when the Bacillus is cultivated in a 
 neutral nutrient solution, meat-broth, especially chicken-broth 
 with a plentiful supply of oxygen at a temperature of 42-43 C. 
 
XIL] Anthrax. 131 
 
 Toussaint and Chauveau obtained the same results at a higher 
 temperature. A culture of this kind ends in the death of the 
 Bacillus, which ensues, according to Pasteur's account, in about 
 a month or a little more than a month. Till this time the 
 Bacillus vegetates without change in its morphological charac- 
 ters, except that the formation of spores is delayed or altogether 
 stopped. That it never takes place is denied by Koch, Gaffky, 
 and Loffler on the ground of direct observation. If the Bacillus 
 is transferred to a fresh culture at any time before death has 
 supervened, it will develope in the normal manner, and even 
 produce normal spores at the proper temperature. If the tem- 
 perature continues to be raised, complete attenuation results in a 
 shorter time ; a few days are required at a temperature of 45 C., 
 a few hours at one of 47 C., a few minutes at one of 50-53 C. 
 The three Berlin observers found that there was a considerable 
 difference between 42 and 43 C. in the time required for total 
 attenuation in correspondence with the temperature-differences 
 of tenths of a degree, the process being accelerated as the 
 temperature rose. 
 
 It follows that if the Bacillus is cultivated at a temperature 
 between 42 and 43 C., we obtain material which will be harm- 
 less to animals in the order of their susceptibility to infection, 
 for instance to rabbits first, after them to guinea-pigs, and lastly 
 to mice ; fluctuations will naturally occur according to indi- 
 vidual susceptibility, age, and other circumstances. 
 
 It has been already stated that the Bacilli are capable of 
 further vegetation after passing through every degree of atten- 
 uation of their virulence before reaching the stage of actual 
 loss of vitality. If their cultivation is continued under optimum 
 conditions they grow in their normal shape and form normal 
 spores, but the successive generations, even when produced 
 from spores, nevertheless retain as a rule the degree of attenua- 
 tion of the first generation; some kill mice for example and 
 are harmless in the case of guinea-pigs, others do not affect the 
 health of mice. Cultures of the latter quality were continued 
 
 K 2 
 
132 Lectures on Bacteria. [$ xn. 
 
 during two years by Koch, Gaffky, and Loffler without any 
 change or any return to virulence. 
 
 The behaviour of Bacilli which have been rapidly attenuated 
 at 4 7-50 C. and at still higher temperatures is different; they 
 recover their virulence when cultivated under the most favourable 
 conditions. 
 
 It is true that a return from the attenuated to the virulent 
 condition is not altogether excluded, even in forms which have 
 been slowly attenuated. Pasteur affirms that if matter, which is 
 not fatal to full-grown guinea-pigs but kills young individuals 
 a day or two old, is taken from one of the latter and used to 
 inoculate other guinea-pigs successively older, a degree of viru- 
 lence is ultimately attained sufficient to kill old animals. Koch 
 and his colleagues have not found these statements confirmed by 
 their results, and though their experiments were somewhat differ- 
 ently arranged, yet they seem to show that no such fixed rule ob- 
 tains in this matter as might be gathered from Pasteur's account. 
 On the other hand the same observers have distinctly proved 
 that there is a return to increased virulence in individual and 
 not very similar cases. 
 
 Lastly, they have also proved that cases of the reverse kind 
 occur, in which the virulence of a culture suddenly diminishes 
 of its own accord, that is without any ascertained external cause; 
 spores from material which killed rabbits and guinea-pigs pro- 
 duced eight weeks later a generation which did not injure these 
 animals but was still fatal to mice. To this class of phenomena 
 belongs perhaps an observation recently communicated by 
 Prazmoswki, according to which a pure culture of Bacillus 
 Anthracis in a nutrient solution entirely lost its virulence with- 
 out apparent cause. I have myself seen the same or a similar 
 case. Buchner's investigation, which bears on this point, will 
 be noticed presently. 
 
 I have already observed that the form of the Bacillus remains 
 unchanged in the virulent and attenuated states. In the main 
 points this is always the case, though some modifications have 
 
xii.] Anthrax. 133 
 
 been observed. Thus it is stated by Koch and his colleagues 
 that the Bacillus which is only strong enough to kill mice 
 fills the capillaries, especially of the lungs, in the form of 
 long filaments, which may often be followed continuously from 
 the capillaries into the larger microscopic vessels, while the 
 more virulent Bacillus is usually present in the capillaries in the 
 form of short rods. 
 
 In Prazmowski's observation the difference between the viru- 
 lent and attenuated forms was, that the rods of the latter kind 
 were motile during several generations, though their motion was 
 slow and dragging in comparison, for example, with that of the 
 hay-bacillus, and that they not only form flakes at the bottom 
 of the nutrient solution which is clear above them, but also rise 
 in it and make it turbid, and form on its surface ' thickish dirty- 
 white films of a slimy consistence.' Exactly the same appear- 
 ance has been observed by myself in meat-extract-solution; 
 there the rods even up to the time of forming their spores were 
 much less united into long filaments than in the virulent forms, 
 and in the surface-films they lay in every direction, and were 
 densely and irregularly compacted together into a felted mass. 
 This mode of grouping is in appearance so unlike that of the 
 common Bacillus, that we are naturally led to assume that we 
 are dealing with a form very like Bacillus Anthracis, but yet 
 specifically distinct from it, which has not allowed the latter to 
 thrive in the solution, the Bacillus perhaps of Koch's malignant 
 oedema ; but the harmlessness of this form, even in the case of 
 small rodents, is against this assumption. 
 
 Buchner undoubtedly observed the same phenomenon, when 
 he grew Bacillus Anthracis through several generations in nu- 
 trient solutions composed of i per cent, of meat-extract, with or 
 without the addition of sugar and peptone, and at a temperature 
 of 35-3 7 C., and kept the cultures in constant movement by 
 help of a rocking-apparatus in order to secure the largest 
 possible supply of oxygen. The products of the cultivation 
 gradually assumed the characters of Prazmowski's modified form. 
 
1 34 Lectures on Bacteria. [ xii. 
 
 Since this form in its want of virulence, its formation of super- 
 ficial films, and its power of independent movement is more 
 like the hay-bacillus, B. subtilis, than the virulent form, Buch- 
 ner maintained that the virulent B. Anthracis had been entirely 
 changed by cultivation into the harmless B. subtilis, and the 
 matter excited much attention, since there was here apparently 
 an evident case of the conversion of a species held to be distinct 
 into another. But, as was shown on page 34, he has not yet 
 proved his point. Buchner certainly tried the reverse process 
 also, and endeavoured to convert the harmless B. subtilis into 
 the virulent B. Anthracis by cultivating successive generations 
 of it in various solutions containing albumen, which I must not 
 enumerate here. The results obtained were for the most part 
 distinctly negative, and the few which were said to be positive 
 are open to so many objections, that without insisting on strict 
 morphological proof we must consider them as quite uncertain. 
 Here too the morphological proof has been omitted. It is quite 
 possible that the usually harmless B. subtilis may by breeding be 
 endowed with an exceptional virulence ; but its specific character 
 would no more be affected by this, than is that of B. Anthracis 
 by its attenuations, nor would the fact that the latter is the 
 ordinary exciting cause of anthrax be rendered at all doubtful. 
 
 Pasteur and Toussaint, led by experience derived from other 
 sources which will be noticed again presently, have attempted 
 with success to use the attenuated Bacillus of anthrax for pro- 
 tective inoculation against the virulent Bacillus. If an animal is 
 inoculated with the Bacillus attenuated to the degree requisite 
 for it, that is for that species, it either does not sicken or it 
 sickens slightly and recovers from the disease. It resists then 
 infection with less attenuated Bacillus, and at the next inocula- 
 tion it resists the Bacillus which possesses the highest degree of 
 virulence. The certainty of these results, and their special im- 
 portance at the same time in reference to the practical art of 
 the breeder, is differently appreciated in different quarters; 
 Koch especially and his colleagues have brought forward well- 
 
XIL] Anthrax. 135 
 
 grounded objections to the praises bestowed on the school of 
 Pasteur. We cannot enter further in this place into these prac- 
 tical questions. The fact, however, of the frequent success of 
 protective inoculation is well established, and is abundantly con- 
 firmed even by those who are opposed to the exaggerated 
 estimate of its practical importance. We record it therefore as 
 a phenomenon of high scientific interest. 
 
 Having now become acquainted with these phenomena relative 
 to Bacillus Anthracis and the disease which it produces, let us 
 enquire how the injurious effects of the virulent Bacillus are 
 brought about, and how the attenuation of the virulence and the 
 operation of protective inoculation just described are to be 
 explained. 
 
 In the present state of our knowledge we shall succeed in 
 answering these questions best if we begin with the second. To 
 prevent misunderstanding I will say beforehand most distinctly, 
 that we can at present only make an attempt to answer these 
 and all other questions, and must wait for our answers to be 
 confirmed or amended by future investigation. 
 
 We begin therefore with the question of the explanation of 
 protective inoculation, and we may formulate it a little differently 
 and extend it by asking how it is that an animal is or becomes 
 unsusceptible to, safe from the attacks of the injurious parasite. 
 Metschnikoff has lately published some investigations which, if 
 confirmed, bring us a step nearer to the understanding of this 
 phenomenon. I report them because they seem to be trust- 
 worthy ; I have not been able to repeat them myself. 
 
 We know that the blood of vertebrate animals contains red 
 blood-corpuscles suspended in the fluid blood-plasma, and be- 
 sides these colourless or white blood-corpuscles or blood-cells 
 in considerably smaller quantity. The lower animals have no 
 red blood-corpuscles, only the colourless blood-cells, which are 
 uncoloured nucleated protoplasmic bodies. They possess a 
 variety of remarkable qualities, but at present we are chiefly 
 concerned with the fact that, like many other protoplasmic 
 
136 Lectures on Bacteria. [$ xn. 
 
 bodies of similar structure, they are subject during their life to 
 constant changes of shape in their soft viscid substance, ex- 
 hibiting undulatory movements of their outline and alternate 
 protrusion and retraction of processes (see Fig. 19). These 
 amoeboid movements, as they are called, are combined with the 
 power of taking up and absorbing solid bodies, or oil-drops, or 
 similar objects into their soft substance. If the foreign body 
 comes into contact with the surface of the amoeboid cell, the 
 latter puts out processes which embrace it, and gradually close 
 over it as the waves close over a drowning animal, so that it 
 lies at last inside the soft cell-substance. It may be cast out 
 again at some future time, but it may also suffer decomposition 
 inside the cell, be killed, and disappear. 
 
 In connection with these well-known facts, and also with the 
 observation made by him in the case of a disease in some small 
 crustaceans caused by the invasion of a peculiar Sprouting 
 Fungus, that the cells of the Fungus were absorbed by the colour- 
 less blood-cells of the animal and decomposed in it, that there 
 was a struggle, so to say, between the parasitic Fungus and 
 the amoeboid cells of the animal, Metschnikoff investigated 
 the behaviour of the colourless blood-cells of the vertebrate 
 animals to the Bacillus of anthrax. He found that the virulent 
 rods when introduced by inoculation into an animal liable to 
 take the fever, such as a rodent, were absorbed by the blood- 
 cells only in exceptional instances. They were readily absorbed 
 by the blood-cells of animals not liable to the disease, as frogs 
 and lizards, when the temperature was not artificially raised 
 (Fig. 1 9), and then disappeared inside the cells. The same thing 
 happened when susceptible animals were inoculated with Bacillus 
 Anthracis which had been attenuated to the harmless state. 
 Chauveau had already stated that the attenuated Bacilli pass into 
 the lungs and liver of the animal and there disappear. From all 
 these data we must assume with Metschnikoff that the Bacillus is 
 harmless because it is absorbed and destroyed by the blood-cells, 
 and injurious because this does not happen ; or at least that it 
 
XIL] Anthrax. 137 
 
 becomes harmless if the destruction by the blood-cells takes 
 place more rapidly and to a greater extent than the growth and 
 multiplication of the Bacillus, the converse being also true. 
 
 If these ideas are correct, and a normally virulent Bacillus 
 is harmless after protective 
 inoculation and in the absence 
 of this is still virulent, we are 
 driven to the further assump- 
 tion that the protective inocu- 
 lation produces this result by 
 giving the blood-cells the 
 power which they did not be- 
 fore possess of absorbing and 
 
 destroying virulent Bacilli. We have no distinct investigations 
 into this point for our guidance, but if we once more accept 
 the views set forth above we must almost necessarily assume 
 that by the actual absorption of less virulent Bacilli the 
 blood-cells of an animal successively acquire the power of 
 absorbing and destroying the more virulent, which would not 
 have been taken up without this preparation. 
 
 The security of an animal from infection by a dangerous 
 parasite which has found its way into its blood, or the suscepti- 
 bility to it, would accordingly depend on the reaction of the 
 blood-cells on the parasite ; and it would be possible to alter 
 their power of reaction by gradually accustoming them as it 
 were to a succession of more and more virulent individuals. 
 In this way we obtain a partial explanation of the effects of 
 protective inoculation with material of increasing virulence. 
 
 But now there is the further question, why are virulent Bacilli 
 scarcely ever taken up by the blood-cells of an unprepared 
 animal, while the attenuated ones are readily absorbed ? Since 
 
 Fig. 19. a blood-cell of a frog in the act of engulphing a rod of Bacillus 
 Anthracis, observed in the living state in a drop of aqueous humour, b the 
 same a few minutes later; the shape of the cell is changed and the bacillus 
 is completely engulphed. After Metschnikoff. Highly magnified. 
 
138 Lectures on Bacteria. [ xn. 
 
 we find no morphological or anatomical differences in the con- 
 curring parts in cases which differ furthest from one another, 
 we can only assume that the cause of the difference in behaviour 
 lies in material differences, differences in the chemical be- 
 haviour of the two objects. And since we are dealing on the 
 one hand with portions of an animal which, as far as we can 
 perceive, is not essentially altered in its collective properties, and 
 on the other hand with a Bacillus which has its properties which 
 are in this case the subject of direct observation essentially 
 altered by attenuation, it follows that the changes in the chemi- 
 cal qualities must chiefly be on the side of the Bacillus. Nor is 
 this at all inconsistent with the phenomena of protective inocu- 
 lation, the accustoming the blood-cells, as was said, to the 
 absorption of a succession of Bacilli each more virulent than the 
 preceding one. On the contrary we know that other amoeboid 
 protoplasmic bodies which absorb solid substances, for example 
 the plasmodia of the Myxomycetes, do become habituated to 
 contact with and probably also to the absorption of bodies with 
 certain chemical qualities, though at first they hastily withdraw 
 from contact with them ; and without further arguments there 
 is good reason for attributing the same power to the blood- 
 cells, because they agree with plasmodia in all other qualities 
 which have any bearing on this point. 
 
 No precise account can at present be given of the nature of 
 the chemical differences between virulent and attenuated Bacilli, 
 and what can be said about it will be mentioned presently. 
 The proximate cause of the attenuation by Pasteur's method 
 is to. be sought not in the effect of oxygen but in the 
 heightened temperature ; this has been shown convincingly 
 by Chauveau and by Koch and his colleagues, who call 
 attention to the fact that the degree and permanence of the 
 attenuation and also the time required for attaining it are di- 
 rectly dependent, other conditions being the same, on the tem- 
 perature and even on small variations of temperature. We know 
 nothing at present respecting the causes of the attenuations 
 
XII.] 
 
 Anthrax. 139 
 
 obtained by other methods than that of Pasteur and of the 
 possible return of virulence. 
 
 If we proceed in the next place to enquire how the parasite 
 causes disease, we find that it is not possible to give a decisive 
 answer ; still there are some definite facts and analogies leading 
 to a conception of the matter which approaches very near to 
 probability. The first fact is the appearance of the carbuncle 
 of anthrax in human subjects infected by inoculation or 
 through a wound. At the spot where the infection has taken 
 place there appears at first a violent local inflammation of the 
 skin, and it is not till 2-3 days later that the general symptoms 
 supervene. The inflammation is specifically different from 
 other violent inflammations of the skin, just as the local symptoms 
 produced by a definite poison with peculiar effects differ from 
 others which are caused by some other poison or by other 
 causes. This, it appears to me, excludes the view sometimes 
 expressed, that the Bacillus becomes the exciting cause of 
 disease by giving rise to merely mechanical disturbances, or 
 simply by withdrawing the oxygen from the living blood in 
 which it vegetates ; it is much more probable that the effect of 
 the Bacillus is peculiar to itself, the result of a specific poison. 
 If this is conceded, then the poison must issue, be excreted 
 from the Bacillus, for it could have no effect if it remained in 
 it. This agrees with MetschnikofFs observation that the same 
 blood-cells readily absorb the Bacillus if it is not virulent, while 
 if it is virulent it is virtually not absorbed. There must be 
 something in the virulent Bacilli which there is not in the 
 others, and it is probable, as was shown above, that this some- 
 thing possesses distinct chemical properties, and it must be on 
 the outside of or at least at the surface of the body of the Bacillus, 
 for if it were only in the inside there would be no reaction 
 with the blood-cells upon their coming into contact with the 
 Bacillus. 
 
 We know nothing of the real nature of the poison which is 
 thus supposed to be excreted by the Bacillus. Attempts to 
 
140 Lectures on Bacteria. [J xn. 
 
 isolate it have been hitherto ineffectual. If the Bacilli in the 
 blood of an infected animal are separated from the fluid of the 
 blood by nitration through porous earthenware, the fluid when 
 injected does not produce anthrax. In these negative results 
 lies the gap in the foregoing line of argument. If we still stand 
 by our previous assumption, it follows that the poison is ex- 
 creted and is operative in very minute absolute quantities, or 
 merely that it decomposes rapidly outside the living blood and 
 loses its efficiency, or both of these suppositions are true. 
 
 The analogies, which may be brought forward in support of 
 the assumption here made that a poison excreted by the Bacillus 
 is the exciting cause of the disease, are drawn partly from the 
 fact that bodies which in extremely small quantities exert a 
 virulent poisonous effect, the poisons of dead flesh, ptomaines, are 
 produced by other Bacteria, though it is true out of dead organic 
 substances, partly and chiefly from Pasteur's observations on 
 fowl-cholera, a disease running a parallel course to that of 
 anthrax and caused by a parasitic Bacterium, of which we will 
 now proceed to give an account. 
 
 But before doing so I have one more remark to make on the 
 attenuation of virulence. If we consider that Bacillus Anthracis 
 is a distinct species, it seems highly remarkable according to our 
 usual experience that it should have a poisonous effect at one 
 time and not at another. Yet similar phenomena are not 
 altogether rare. It will be sufficient to mention one example, 
 that of the sweet and bitter almond to which attention was first 
 called by Nageli, if I am not mistaken, in connection with the 
 subject which we are considering. The bitter almond is 
 poisonous from the amount of amygdalin which it contains, 
 though it is not very dangerous to human beings ; the sweet 
 almond contains no amygdalin and is not poisonous. The 
 sweet almond tree does not differ specifically from the bitter ; a 
 tree with bitter seeds may be produced from a sweet seed ; bitter 
 and sweet seeds may even be borne on the same tree in flowers 
 and fruits not morphologically distinguishable from each other. 
 
xii.] Fowl-cholera. 141 
 
 We do not at all know the origin or cause of this difference, and 
 the instance cannot therefore help us to an actual explanation 
 of the phenomenon before us ; it only shows that we are not 
 dealing with a peculiarity confined to Bacteria or to a single 
 Bacterium, but with a special case of a not uncommon series of 
 phenomena. 
 
 Fowl-cholera or fowl-plague (57) is the name given to 
 a disease which attacks domestic poultry, and which shows 
 a similar behaviour to that of anthrax in the points with which 
 we are at present concerned. We learn from Pasteur's researches 
 that it occurs in fowls in an acute and in a chronic form. 
 Characteristic symptoms of the former are a state of profound 
 torpor or stupefaction ; the bird sits with closed eyes and staring 
 feathers perfectly still and taking no notice of anything about it ; 
 this is followed by diarrhoea produced by inflammation and ulcer- 
 ation of the intestinal canal. Dissection also discloses abscesses 
 in different organs, fatty degeneration of the muscles, and other 
 symptoms. Death usually takes place in from 2-2 1 days, recovery 
 being rare. The chronic form shows similar symptoms but 
 with less violence, in some cases only local abscesses ; these may 
 continue for many weeks and the bird often recovers. 
 
 Dissection shows the presence of large numbers of a small 
 Micrococcus in the blood and abscesses, and on the intestinal 
 mucous membrane of the sick birds, and of those that have 
 died of the disease, really therefore in all parts of the body. 
 The cells of the Micrococcus, according to Kitt, are round, 
 from 0-3 to 0-5 /x in size, often united in pairs, and sometimes 
 also grouped together in larger numbers. The Micrococcus 
 has no power of locomotion, and no distinct spores have been 
 observed. 
 
 The Micrococcus of fowl-cholera may be grown outside the 
 living bird ; according to Kitt on the usual media of cultivation, 
 gelatine, blood-serum, potatoes; according to Pasteur it de- 
 velopes with especial luxuriance in neutralised chicken-broth. A 
 supply of oxygen is necessary for its vegetation. It sinks to the 
 
142 Lectures on Bacteria. [ xn. 
 
 bottom of Pasteur's culture-fluid when vegetation has ceased 
 and the nutrient-material is exhausted, and will remain there 
 alive and capable of renewed vegetation in a suitable substratum 
 for about eight months if the air has access to it, for a longer time 
 if air is excluded, as in hermetically sealed flasks. 
 
 If the Micrococcus is taken fresh from a sick or dead bird 
 or from its excrements, or from an artificial culture abso- 
 lutely free from any diseased part of the bird, and introduced 
 into a healthy bird, the minutest possible quantity of it, ex- 
 hibiting ordinary growth and multiplication, will reproduce the 
 disease. Infection is obtained by inoculation in or beneath 
 the skin, and by introduction of the Micrococcus with the 
 food into the digestive canal. Pasteur succeeded in com- 
 municating the disease by inoculation to mammals as well as 
 to birds ; rabbits thus inoculated died ; in the case of guinea- 
 pigs abscesses only formed at the place of inoculation, and 
 these contained a large quantity of the Micrococcus, but 
 they did not spread and ultimately healed. Kitt has extended 
 these experiments with similar results to mice and sheep and to 
 a horse. 
 
 Enough has been said to show that in this Bacillus, as in that 
 of anthrax, we have a facultative parasite specifically capable of 
 causing disease ; but its history and manner of life, especially 
 as regards the saprophytic sections of its development are not as 
 well known to us as those of Bacillus Anthracis. 
 
 Pasteur further discovered that the Micrococcus loses to some 
 extent its power of infection when it is kept some time exposed 
 to the air ; the number of successful inoculations and the se- 
 verity of the attack caused by them diminish with the age of the 
 matter used in inoculation. The cases mentioned before of 
 slighter attacks of the disease ending in recovery are chiefly 
 cases of inoculation of this kind. We may say therefore in 
 words which have been used before that age produces an 
 attenuation of the power of infection or virulence of the 
 Micrococcus. 
 
xii.] Fowl-cholera. 143 
 
 Individual birds, which had recovered from the disease, 
 were generally but not always found to be no longer susceptible 
 to virulent infection, to be secure against a fresh attack, and 
 on this Pasteur founded the ideas with regard to protective 
 inoculation and his method of employing it which he proceeded 
 to extend to anthrax also. 
 
 When the fluid of a fresh culture in broth was separated by 
 filtration from the Micrococcus, which cannot be done by filtra- 
 tion through paper, for the Bacteria invariably pass with it through 
 the paper, but can be managed by means of filtration through 
 porous earthenware, the fluid was not in a condition to produce 
 the disease in the perfect form, not even when all the consti- 
 tuents contained in solution in 120 grammes of it were injected 
 into the blood of a fowl. But one characteristic symptom of 
 the disease, the stupor, was produced; the birds were sleepy 
 and as if stupefied after infection, continuing in this state about 
 four hours, and then returning to their normal state of health. 
 
 The observation, if established, shows that in this case a nar- 
 cotic poison separable from the Bacterium was actually disengaged 
 from it, and this is the reason why the fowl-cholera is especially 
 instructive in judging of the effects of parasites of this kind in 
 the production of disease. That the effect of the poison in these 
 experiments was comparatively slight and transitory, is to be 
 explained by the small amount of it in the fluid, and by the fact 
 that like other poisons it is either decomposed in the infected 
 fowl or is withdrawn from it with the normal secretions. The 
 case is different when the poisonous organism itself is present in 
 the fowl, apart from the circumstance that the conditions are 
 then probably more favourable for the formation of the poison. 
 While the poison is being perhaps constantly decomposed within 
 the fowl or is being removed with the normal secretions, it is 
 constantly being produced by the parasite, and what has been 
 removed is replaced ; thus the symptoms of the disease neces- 
 sarily become more permanent and more severe, and ultimately 
 also more complicated. Further complications also arising from 
 
144 Lectures on Bacteria. [$ xm. 
 
 the more strictly mechanical effects of the parasite are of course 
 not impossible. 
 
 XIII. 
 
 Causal connection of parasitic Bacteria with infectious 
 diseases, especially in warm-blooded animals. Intro- 
 duction. Relapsing fever. Tuberculosis. Gonorrhoea. 
 Cholera. Traumatic infectious diseases. Erysipelas. 
 Trachoma. Pneumonia. Leprosy. Syphilis. Cattle- 
 plague. Malaria. Typhoid fever. Diphtheria. In- 
 fectious diseases in which the presence of conta- 
 gium vivum has not been demonstrated. 
 
 i. I SHOULD have wished to have added to the foregoing 
 two examples of facultative parasites which cause disease, one 
 example at least of a strictly obligate parasite, but I am unable 
 to find even one which is sufficiently well known to allow a 
 detailed account to be given of it. All that can be produced on 
 this point will therefore be included in the following summary, 
 which is intended to contain in a few words the most important 
 part of the knowledge which we at present possess of the nature 
 of Bacteria as the exciting causes of infectious diseases in warm- 
 blooded animals, and especially in man (58). 
 
 By the term infectious diseases we mean all those forms of 
 disease which are only found where they are conveyed from a 
 sick person to a healthy one so far as the particular disease is 
 concerned, or the origin of which is confined to localities of a 
 particular character. The former kind are known as contagious 
 diseases, such as scarlet fever, measles, small-pox ; the latter, of 
 which malarial fever is the best known example, are termed 
 miasmatic diseases. If the two conditions are combined, we may 
 speak of miasmo-contagious disease and that in two senses ; we 
 may mean firstly that a disease may be caught in certain localities, 
 or by infection from person to person independently of locality 
 of miasmatic character, or secondly that a disease is indeed 
 
xiii.] Causal connection with infectious disease. 145 
 
 contagious, but requires the existence of previous miasmatic 
 infection in the person who is to take it. It should be ob- 
 served also, that up to recent times the term infectious disease 
 was only used when the exciting cause of infection, the con- 
 tagium or miasma, was only imperfectly understood. If disease 
 was caused by known parasites, such as lice or entozoa, trans- 
 ferable from one person to another or only to be procured in 
 certain localities with special characters, it was not called in- 
 fectious but parasitic. 
 
 It was natural that some ideas should be entertained respect- 
 ing the general qualities of the unknown and invisible contagia 
 and miasmata, and it was assumed, not without reason, that 
 they were special particles of matter which were efficacious for 
 infection in a state of the most minute subdivision and in the 
 most infinitesimal quantities. 
 
 The qualities of living beings were for a long time ascribed 
 by some observers to these infectious particles or contagia, as 
 we may now usually call them, and first of all in the period of 
 history from which we have received the terms 'contagium 
 vivum ' or ' animatum/ then used in a somewhat obscure and 
 indefinite sense. The traditional expression contagium vivum 
 received a more precise meaning in 1840 from Henle, who in his 
 ' Pathologischen Untersuchungen ' showed clearly and distinctly 
 that the contagia till then invisible must be regarded as living 
 organisms, and gave his reasons for this view. His argument may 
 be briefly stated in the following manner. The contagia have 
 the power, possessed as far as we know by living creatures only, 
 of growing under favourable conditions, and of multiplying at 
 the expense of some other substance than their own and 
 therefore of assimilating that substance. The quantity, certainly 
 minute, of the contagium which communicates infection to 
 any one who pays a hasty visit to a person suffering from an 
 infectious disease, has the power of multiplying enormously in 
 the body of the infected person, for the latter is able to give the 
 infection to an unlimited number of healthy but susceptible 
 
146 Lectures on Bacteria. [I xm. 
 
 persons, and therefore to part again for an unlimited number of 
 times with the same minute portion of contagium which he 
 himself received. But if we are forced to recognise the charac- 
 teristic qualities of living beings in these contagia, there is no 
 good reason why we should not regard them as real living 
 beings, parasites. For the only general distinction between 
 their mode of appearance and operation and that of parasites is, 
 that the parasites with which we are acquainted have been seen 
 and the contagia have not. That this may be due to imperfect 
 observation is shown by the experiments on the itch in 1840, 
 in which the contagium, the itch-mite, though almost visible 
 without magnifying power, was long at least misunderstood. 
 It was only a short time before that the microscopic Fungus, 
 Achorion, which causes favus, was unexpectedly discovered, as 
 well as the Fungus which gives rise to the infectious disease in 
 the caterpillar of the silkworm known as muscardine. Other and 
 similar cases occurred at a later time, and among them that of 
 the discovery of the Trichinae between 1850 and 1860, a very 
 remarkable instance of a contagious parasite long overlooked. 
 Henle repeated his statements in 1853 in his 'Rationelle Patho- 
 logic/ but for reasons which it is not our business to examine 
 here, his views on animal pathology met with little attention or 
 approval. 
 
 It was in connection with plant-pathology that Henle's views 
 were first destined to further development, and obtained a firmer 
 footing. It is true that the botanists who occupied themselves 
 with the diseases of plants knew nothing of Henle's pathological 
 writings, but made independent efforts to carry on some first 
 attempts which had been made with distinguished success in 
 the beginning of the century. But they did in fact strike upon 
 the path indicated by Henle, and the constant advance made 
 after, about the year 1850, resulted not only in the tracing back 
 of all infectious diseases in plants to parasites as their exciting 
 cause, but in proving that most of the diseases of plants are due 
 to parasitic infection. It may now certainly be admitted that 
 
$xm.] Causal connection with infectious disease. 147 
 
 the task was comparatively easy in the vegetable kingdom, partly 
 because the structure of plants makes them more accessible to 
 research, partly because most of the parasites which infect them 
 are true Fungi, and considerably larger than most of the con- 
 tagia of animal bodies. 
 
 From this time observers in the domain of animal pathology, 
 partly influenced, more or less, by these discoveries in botany, 
 and partly in consequence of the revival of the vitalistic theory 
 of fermentation by Pasteur about the year 1860, returned to' 
 Henle's vitalistic theory of contagion. Henle himself, in the 
 exposition of his views, had already indicated the points of 
 comparison between his own theory and the theory of fermenta- 
 tion founded at that time by Cagniard-Latour and Schwann. 
 
 Under the influence, as he expressly says, of Pasteur's 
 writings, Davaine recalled to mind the little rods first seen by 
 his teacher, Rayer, in the blood of an animal suffering from 
 anthrax, and actually discovered in them the exciting cause of 
 the disease, which may be taken as a type of an infectious 
 disease both contagious and miasmatic also, in so far as it 
 originates, as has been said, in anthrax-districts. This was, in 
 1863, a very important confirmation of Henle's theory, inasmuch 
 as a very small parasite, not very easy of observation at that 
 time, was recognised as a contagium. It was some time before 
 much further advance was made. Rather the too great zeal of 
 inexperienced observers, especially excited by the cholera-epi- 
 demic of 1866, led to a so-called searching for parasites, barren 
 of all but mischievous results, which was the more calculated to 
 repel more earnest observers because for a time it attracted 
 some measure of applause. These are things which are now 
 long passed away and require no further notice. 
 
 Since about the year 1870 more general attention has been 
 again directed to these questions. The number of publications 
 discussing or bearing upon them is rapidly increasing, and we 
 cannot follow them here in detail. Prominent among them, as 
 new and especially suggestive attempts to deal with the subject, 
 
 L 2 
 
148 Lectures on Bacteria. [$ XIIT. 
 
 are Conn's and Billroth's works already mentioned (1, 6), and 
 those of von Recklinghausen and Klebs on the more specially 
 pathological side ; it is the merit of Klebs more particularly to 
 have clearly indicated not only the nature of the problem as 
 conceived by Henle, whom he expressly follows, but also the 
 details of the ways and methods to be adopted for its solution, 
 and to have pursued them himself, though sometimes perhaps 
 with more zeal than discretion. Pasteur and his school pursued 
 the same course independently. Thus questions and experi- 
 ments were framed and knowledge acquired with constantly 
 increasing precision and results. The latest advance to be 
 recorded begins with the participation of Robert Koch in the 
 work of research since 1876. He may claim to have gone 
 forward as a highly intelligent observer on the paths marked 
 out by his predecessors without precipitancy, and with careful 
 use of all improvements in morphological investigation and in 
 microscopical and experimental methods. Hence he was the 
 first to obtain clear results in cases which up to that time had 
 always been disputed, as is shown by our account in a former 
 lecture of the aetiology of anthrax, the final settlement of which 
 is due to his investigations ; he has also shown what must be 
 done to ensure progress in researches of this kind. 
 
 The result of all these efforts is the same as that which was 
 arrived at in plant-pathology thirty years before. Firstly, it is 
 certain that in a number of cases the contagium is a micro- 
 scopic parasite, and that certain diseases, the infectious nature 
 of which was formerly denied or was doubtful, are infectious 
 diseases of this kind. Secondly, the same conclusion is rendered 
 at least highly probable in other cases. Thirdly, there remains 
 a very considerable number of diseases in which the parasite 
 has been sought for, but has either not yet been found, or its 
 existence is doubtful. 
 
 Further, it has been proved that, with some exceptions, 
 especially of skin-diseases and similar affections in which true 
 Fungi of a relatively large size are concerned, by far the most 
 
f XIIL] Causal connection with infectious disease. 149 
 
 important parasites of contagion in warm-blooded animals 
 hitherto certainly determined are Bacteria. 
 
 We may note as consequences of what has now been said, 
 firstly, that Henle's doctrine has become a widely-accepted 
 dogma. There is no objection to this, if we put in the place of 
 belief that intelligent personal conviction which is distinctly 
 directed toward a particular view, but does not lose sight of the 
 possibility that it may some day be corrected or altered. That 
 the parasite required by the theory has not yet been found is no 
 reason for abandoning it, for the parasite may very easily have 
 been overlooked, owing to its extreme minuteness, or its power 
 of refraction, or because the observer has not learnt the right 
 place or time to look for it. When Henle founded his doctrine 
 in 1840, the Bacillus of anthrax had never been seen; the 
 Trichinae had been seen, but no one suspected that they were 
 the cause of disease. 
 
 The second result is that at present in almost every doubtful 
 or questionable case, it is only for Bacteria that search is made. 
 This is wrong in principle ; it may be practically right to search 
 for such forms as present experience shows are the most likely 
 to be found. But it should be remembered that organisms of 
 another kind may make their appearance unexpectedly, about 
 which we at present perhaps know very little. It is not so long 
 ago, that we knew very little about Bacteria and expected them 
 as little. That this is not idle talk is shown by some surprising 
 experiences recorded in connection with plant-pathology and by 
 the history of pe'brine which will be noticed presently. 
 
 Thirdly, if belief is stronger than the critical faculty, there is 
 great danger of concluding at once from the presence of a Bac- 
 terium that it is the exciting cause of disease for which we may 
 be seeking. From what we learnt in Lecture V on the wide 
 diffusion of Bacteria possessing full powers of development it 
 will at once be seen that Bacteria may be developed in a diseased 
 body before or after death, and that a particular form may be 
 present as a characteristic feature and even constantly and exclu- 
 
150 Lectures on Bacteria. [} xm. 
 
 sively in a particular disease, and therefore have high diagnostic 
 value, without being the contagium which causes the disease. 
 To make sure of this it is absolutely necessary to experiment with 
 pure material and to obtain a clear positive result ; there must 
 therefore be a pure separation of the parasite to be examined 
 from all admixtures, a pure infection of the proper subject for 
 experiment with pure matter, and the strictest control and 
 criticism of the result. The example of anthrax described above 
 will illustrate these rules. Without successful experimentation 
 there is always a gap in the proof which cannot be filled up by 
 other arguments, however well adapted they may be to serve as 
 the foundation of a personal conviction. It is true that the latter 
 may persist in spite of defective experimental proof. A parasite, 
 as has been before explained, does not thrive, or does not thrive 
 equally well in every host-species; it can attack and cause 
 disease in one and not in another. The experiment therefore in 
 the case in question may give no positive result, because the 
 right, that is the susceptible, species of warm-blooded animal was 
 not employed. This point must be specially attended to in the 
 case of infectious diseases which attack human beings chiefly. 
 We cannot or must not experiment freely with human beings, 
 but must trust in the main to experiment on other warm-blooded 
 animals, and this may be the only reason why that in certain 
 cases, some of which will be noticed further on, the results of 
 experiment have as yet remained doubtful or negative. 
 
 Enough has been said to give inexperienced persons an idea 
 beforehand of the reasons why we may have to speak here of 
 doubtful cases and doubtful statements. 
 
 We will now proceed to a consideration of the facts. Our 
 object, as was said before, is to bring forward whatever is most 
 important in connection with the Bacteria which are the exciting 
 causes of disease. A minute discussion of the diseases them- 
 selves does not fall within the plan of these lectures, and must 
 be sought in medical publications. 
 
 Whatever peculiarity there may be in each individual case, we 
 
xiii.] Relapsing fever. 151 
 
 are constantly confronted in dealing with the main points of our 
 subject with similar facts and questions to those which were 
 considered at some length in connection with anthrax and fowl- 
 cholera ; they form part of the great series of facts and questions 
 relating to parasitism, of which it was attempted to give a con- 
 cise review in Lecture X. 
 
 With this brief reference to these previous expositions we now 
 proceed to consider a few comparatively well-known cases. 
 
 2. Relapsing fever, febris recurrens (59), is a disease which is 
 widely spread in Asia and Africa, is endemic in Russian Poland 
 and Ireland, and sometimes finds its way into other countries 
 of Europe. It is communicated directly from the body of one 
 person to another or through the intervention of articles of daily 
 use. In 5-7 days after infection violent fever sets in with other 
 symptoms which need not be described here, and usually lasts 
 another 5-7 days, and is then followed by a period of absence 
 of fever for about the same number of days. Then comes a 
 relapse into the fever state, and the same alternation may be 
 repeated several times, usually with a favourable ending. 
 
 During the attack a slender Spirillum, resembling Spirochaete 
 Cohnii (Fig. 16, <?), sometimes 40/11 in length and exhibiting 
 active movements, is found in abundance in the blood of the 
 patient which is often of a dark-red colour; discovered by 
 Obermeier in 1873 it was named after him Spirochaete Ober- 
 meieri ; it disappears during the interval when there is no fever. 
 
 The disease is conveyed to men and monkeys when they are 
 inoculated with the blood of a fever-patient containing Spiro- 
 chaete. Blood taken during the interval of freedom from fever 
 and therefore free from the Spirochaete does not produce the 
 disorder after inoculation. Experiments in the inoculation of 
 other animals were always without result. Attempts to cultivate 
 the Spirochaete outside the body of the animal have not as yet 
 been successful. 
 
 From these facts it may properly be assumed that the Spiro- 
 chaete is the contagium of relapsing fever, though we are still 
 
152 Lectures on Bacteria. [ xm. 
 
 very imperfectly acquainted with its life-history, for we have 
 no certain information as to its place of sojourn during the in- 
 tervals of the fever, the form and mode of its conveyance from 
 one person to another, the formation of spores if any, or other 
 resting states. 
 
 3. One of the most important results of the researches into 
 the Bacteria which are the exciting causes of disease is the dis- 
 covery of the contagium of tuberculosis, the Bacillus of tubercle 
 long since rendered familiar to us by Koch's publications (60). 
 Tuberculosis has received its name from the formation of new 
 substance or the degeneration by which it is characterised, and 
 which appear in the form of small knots or tubercles in the 
 tissue of the organs. The formation of tubercle is best known 
 in the lungs as pulmonary-tuberculosis, pulmonary consumption, 
 but it may occur in any organ and the lymphatic glands are 
 particularly subject to it. 
 
 Tuberculosis attacks warm-blooded animals of every species 
 as well as man, and especially our ordinary domestic animals 
 and those used for experiments. The tuberculosis of horned 
 cattle is known by the name of pearly disease, bovine tuberculosis. 
 Different species show different degrees of susceptibility ; the 
 field-mouse is highly susceptible to infection, the domestic mouse 
 only slightly. The primary anatomical changes in the formation 
 of tubercle are in all cases the same. The succeeding ones and 
 the general character of the disease may be very dissimilar. 
 
 In tubercle, at least in the fresh state, Koch and simulta- 
 neously with him Baumgarten demonstrated the presence of a 
 characteristic rod-shaped Bacillus. According to these observers 
 it is always there, though in very unequal quantities in different 
 cases. It passes into the ejected matter, the sputum of pulmo- 
 nary tuberculosis, and may be found in it. With due care it may 
 be kept pure and be cultivated pure through repeated generations 
 on stiffened blood-serum or in infusion of meat. 
 
 Tubercular matter containing Bacilli, or still better the purely 
 cultivated Bacillus, introduced beneath the skin of susceptible 
 
xiii.] Bacillus of tubercle. 153 
 
 animals or injected into a blood-vessel or into a cavity of the 
 body, or pure Bacillus-material inhaled in a state of fine division 
 suspended in water, resulted in the formation of tubercle with 
 its consequences in every case without exception Koch 
 experimented on 217 individuals of susceptible species of 
 animals (rabbits, guinea-pigs, cats, field-mice), besides animals 
 used in control-experiments and individuals of less susceptible 
 species and the Bacillus was in every case found in the tuber- 
 cles. In every case also the place where the tubercle appeared, 
 its frequency and distribution, and the line of distribution through 
 the body answered the expectations founded on the mode of 
 infection and the spot where the infecting matter was applied. 
 These results, still further strengthened by control-experiments, 
 established the infectious nature of tuberculosis, and the conta- 
 gious character of the Bacillus, which had indeed been previously 
 concluded on other grounds. 
 
 Such observations on the Bacillus itself as have been published 
 leave much to be desired as regards its morphology. Observers 
 have been generally satisfied with proving its presence, and the 
 proof has been rendered easy by its peculiar behaviour with 
 aniline colouring matters. In contrast to the great majority of 
 other known Bacteria, it slowly and with difficulty takes in alka- 
 line solution of methylene blue or saturated solution of methyl- 
 violet, absorbing them only in the space of several hours or 
 after being heated, but it obstinately retains the colour it has 
 acquired, while other Bacteria are quickly decolorised by certain 
 reagents, for example, dilute nitric acid. By this peculiarity 
 in their behaviour as well as by their shape and size, the Bacilli 
 are comparatively easy to recognise and distinguish from other 
 species. . In form they are slender rods which are sometimes 
 curved or bent at an angle, and reach a length of i'5-3'5/*. 
 Neither in the natural nor in the coloured state can transverse 
 septation as a rule be observed. Endogenetic spores are found 
 in them, both in cultures and in the body and sputa of diseased 
 animals ; these according to Koch's brief account must answer 
 
154 Lectures on Bacteria. [ xm. 
 
 to the spores of endosporous Bacilli, but no further description 
 is given of them. Judging from the figures of sporogenous speci- 
 mens, and assuming that this species does not differ altogether 
 in behaviour from other endosporous Bacteria (see page 15), 
 the rods must be segmented in the same way as those of Bacillus 
 Megaterium described above, for they are represented with 4-6 
 spores standing close in a row one above another, as in Fig. i, r. 
 If our assumption and the account given is correct, each of these 
 spores must lie in a short segment-cell. This agrees with the 
 fact, that in coloured preparations the rods are sometimes found 
 divided by narrow hyaline transverse septa into a series of seg- 
 ments not longer than broad, such as Zopf figures in his third 
 edition. To call these segments Cocci is only playing with words. 
 If young vegetating rods are divided into long segments, this is 
 another point of agreement with Bacillus Megaterium. After 
 this description I abstain from giving a figure of this species ; a 
 drawing of what has been at present seen would represent a 
 simple or interrupted black stroke. In Fig. i, <$-_/" and r corre- 
 spond with our present knowledge of the form of the Bacillus of 
 tubercle, except that the length of the rods in the latter species 
 is on an average not greater than the breadth of those of Bacillus 
 Megaterium in the figure. 
 
 The living rods, according to Koch, are not motile. When 
 grown on stiffened blood-serum they do not liquefy it, but 
 remain on the surface, and there even when developed in com- 
 parative abundance they form thin dry scales of small extension, 
 which are shown under the microscope to consist of sinuously 
 curved swarms and bundles of single rods. 
 
 The Bacillus of tubercle grows slowly as compared with most 
 other Bacteria, and in this respect resembles the Bacterium of 
 kefir. In cultures on serum 10-15 days elapse before growth 
 can be detected by the unaided eye. The result of an inocula- 
 tion is not apparent in less than 2-8 weeks. 
 
 The attempts to cultivate this species outside the living animal 
 on any other nutrient substrata than those above-mentioned 
 
xiii.] Bacillus of tubercle. 155 
 
 have not been successful ; the cardinal points for the tempera- 
 tures of vegetation are those given on page 51. 
 
 The Bacillus of tubercle offers a somewhat high degree of 
 resistance to injurious influences from without, and is thus able 
 to preserve its powers of infection. It can bear temperatures 
 approaching the boiling point, though it is soon killed if it is 
 heated in a thoroughly moist condition. It was not affected by 
 desiccation during a period of 186 days, or by being kept in 
 putrefying sputum for 43 days. The experiments on its powers 
 of resistance have chiefly been made with sputum containing the 
 Bacilli. No attempt has been made to determine precisely how 
 far these powers of endurance are confined to the spores or 
 belong also to the vegetative rods, but our experience in other 
 cases would lead us to suppose that they belong chiefly to the 
 spores. 
 
 These facts taken together give a satisfactory explanation of 
 the appearance of tuberculosis as the result of infection with the 
 Bacillus. Every one knows how widely spread the disease is, 
 even if we think only of pulmonary tuberculosis ; a seventh part 
 on an average of the deaths of human beings are caused by this 
 form of the disease. The Bacillus is generally present, capable 
 of development and in a virulent condition, in the excretions of 
 those suffering from tuberculosis. The expectorations of con- 
 sumptive persons often during months and years must be espe- 
 cially but by no means exclusively taken into account in this 
 connection. The Bacillus was absent from 44 only of the 982 
 specimens of sputa examined by Gaffky. It is clear that the 
 Bacillus is communicated in large numbers to these excretions, 
 and that when they dry up, it must be disseminated with the 
 dust and in other ways. There is therefore abundant oppor- 
 tunity for infection in the ordinary intercourse of human beings. 
 We need not enter more minutely into this point, and to discuss 
 the mode in which the Bacillus spreads in the body which has 
 once become infected would also lead us too far into medical 
 details. That a good deal depends on the susceptibility of the 
 
156 Lectures on Bacteria. [ xm. 
 
 subject to be infected to the results of infection is shown by the 
 fact, that in sick-rooms and institutions in which consumptive 
 patients remain the year through, it is not every one who is suc- 
 cessfully infected with tuberculosis. This fact is in accordance 
 with the general knowledge which we possess of individual or 
 specific differences in susceptibility to the attacks of parasites. 
 
 The foregoing facts and views are not affected by the state- 
 ments of Malassez and Vignal, who describe a form of tuber- 
 culosis with a copious growth of Micrococcus, which they call 
 'tuberculose zoogloique,' and in which they sometimes found 
 the Bacillus and sometimes not. Supposing these accounts to 
 be correct, we must assume with the clear results of Koch's in- 
 vestigations before us that there is either some complication 
 here, or that we are dealing with some disease resembling 
 ordinary tuberculosis but different from it in so far as it is caused 
 by a different parasite. 
 
 4. Gonorrhoeal affections (61). These are inflammations 
 of the mucous membrane of the urethra and of the conjunc- 
 tiva of the eye accompanied by suppuration and occurring 
 in the human species. Purulent conjunctivitis in new-born 
 children, ophthalmia neonatorum, may certainly be classed 
 with them. 
 
 One of the characteristic peculiarities of these maladies is that 
 they are highly infectious, and it has long been known that in- 
 fection is due to the purulent secretion of the patient. The 
 infection of healthy human eyes takes place, as Hirschberg says, 
 with the certainty of a physical experiment. With the same 
 certainty there is found in the infectious matter a large Micro- 
 coccus, which was discovered by Neisser and named by him 
 Gonococcus (Fig. 20), chiefly appearing to be attached to the 
 surface of the epithelial and pus-cells, according to recent 
 observations really penetrating a slight distance into the body 
 of the cells, less often lying between them. It should be added 
 that the number of the cells beset with the Gonococcus is always 
 relatively small and varies from case to case. 
 
f xiii.] Gonorrhoeal affections. 157 
 
 The cells of the Gonococcus are roundish in shape and of 
 some size, about 0-8 /* in diameter, often attached together in 
 pairs corresponding to their partitions, separated in the full-grown 
 state by a hyaline gelatinous intervening substance, and often 
 distributed in large numbers and at tolerably regular distances 
 on the surface of the pus-cells. It is un- 
 certain whether this superficial arrangement 
 is due to successive partitions taking place 
 alternately in two directions, or to a cor- 
 responding displacement with the partition 
 always in the same direction ; I see nothing Fig. 20. 
 
 in the observed facts to compel us to adopt the first as- 
 sumption. 
 
 Gonococcus is not found in other inflammations of the 
 mucous membranes in question, and other Bacteria do not give 
 rise to the phenomena of gonorrhoea. These facts make it 
 probable with the aid of analogy that the infectious nature of 
 the gonorrhoeic secretion is due to the presence of the Coccus, 
 that this is the active contagium. 
 
 Warm-blooded animals other than man are, as far we know, 
 either not susceptible to gonorrhoeic infection or take it with 
 difficulty ; a very large majority of the experiments on animals 
 with the secretion from the eye were unsuccessful. 
 
 Cultures of Micrococcus Gonococcus outside the living 
 patient seldom succeed. Yet some are said to have been suc- 
 cessful, those for example of Hausmann from the secretion from 
 the eye of an infant on stiffened blood-serum, and those of 
 Bockhardt and Bumm from the secretion from the urethra ; 
 
 Fig. 20. Micrococcus Gonococcus, Neisser. From the secretion from 
 the conjunctiva of a child treated for Ophthalmia neonatorum. Four 
 pus-cells with Micrococcus attached, from a preparation coloured with 
 methyl-violet. The pale-coloured pus-cells with their nuclei are faintly 
 shown in the drawing in order to make the Micrococcus more apparent. 
 n outline of an isolated cell of Micrococcus and of a pair of cells formed by 
 bipartition. Magn. 600 times, with the exception of n, which is more 
 highly magnified. 
 
158 Lectures on Bacteria. [$ xm. 
 
 the careful observations of the latter author leave no room for 
 doubt. The introduction of the Coccus from a pure culture 
 into the eye of a new-born rabbit by Hausmann, and into the 
 eye and urethra of a human subject by Bockhardt and Bumm, 
 communicated the infection. It appears from Bumm's obser- 
 vations on the conjunctiva of the human eye, that the Micro- 
 coccus penetrates between the epithelial cells into the papillary 
 body of the mucous membrane, multiplies and spreads in these 
 spots and later also in the purulent secretion, and is ultimately 
 stopped in its further advance and got rid of by regeneration of 
 the epithelium and secretion of pus. The case examined by 
 Bockhardt showed more complicated phenomena. Bumm's 
 excellent monograph should be consulted for the details. 
 
 I have put together relapsing fever, tuberculosis, and gonor- 
 rhoea, different as they are from one another, because if we 
 once put the doubts and the gaps in our knowledge on one side, 
 and take probability for certainty, they supply us with examples 
 of actual obligate parasitic Bacteria. 
 
 Spirochaete Obermeieri is, as far as we at present know, 
 strictly obligate, inasmuch as it can only be conveyed from one 
 person to another without digression into saprophytism, and is 
 confined to men and apes. 
 
 The Bacillus of tubercle and Gonococcus may certainly be 
 cultivated as saprophytes, a facultative saprophytism cannot be 
 denied them. But this character can scarcely be taken into 
 consideration in their case ; not in that of the Bacillus of tubercle, 
 as Koch urges, because the conditions of its vegetation as a 
 saprophyte are of such a kind and so limited, that they will 
 scarcely ever be found except in an apparatus contrived for the 
 special purpose, nor yet in that of Gonococcus for similar 
 reasons. This follows at once from our experience in 
 general, and it follows further that the resisting power of 
 the Gonococcus is very small, and its dissemination for the 
 purpose of infection, as for example in dust after desiccation, 
 is not worth consideration. Gonorrhoeic affections are scarcely 
 
XIIL] Asiatic cholera. 159 
 
 less common than tuberculosis ; their secretions are scattered 
 about and the Gonococcus with them. If the Gonococcus were 
 capable of saprophytic vegetation under ordinary natural con- 
 ditions, it is hardly to be supposed that infection would not 
 sometimes take place in some other way than from one person 
 to another. This, however, notwithstanding some quite doubtful 
 and isolated accounts, is not the case. 
 
 5. Asiatic cholera (75) may now be very fairly reckoned 
 among the comparatively well-known infectious diseases, which 
 we are at present considering. As early as the beginning of 
 the year 1850, Pacini believed that he had found a contagium 
 vivum of this disorder in the Bacteria, or Vibrios as he terms 
 them, which he observed in the intestinal canal and its evacua- 
 tions. Some time after (1867) Klob examined the contents of 
 the intestinal canal, and the evacuations of patients suffering 
 from Asiatic cholera, and likewise found Bacteria present in 
 them in considerable quantities ; and starting with the assump- 
 tion that these organisms are instruments of decomposition, he 
 showed it to be probable that these Bacteria set up the disease 
 in the intestinal canal, and spread it from thence to other parts 
 of the body. Our knowledge of the Bacteria had not then 
 reached the point at which attempts could be made to dis- 
 tinguish more precisely between the various forms found in the 
 intestine and in the dejecta and to separate them from one 
 another. The absurd notion, entertained in other quarters be- 
 tween the years 1860 and 1870, of referring the cholera-con- 
 tagium, Bacteria included, to ordinary moulds and hypothetical 
 parasites of the rice-plant, and the fact that Bacteria apparently 
 quite similar to those of Klob were found in the intestinal canal 
 of persons who were not suffering from cholera, had the effect 
 of withdrawing attention once more from these and other efforts 
 to discover the contagium vivum of this disease. In India, 
 the perennial home of the pestilence, the researches conducted 
 at a later time by English physicians gave no certain and positive 
 results. 
 
160 Lectures on Bacteria. [ xiu. 
 
 Our knowledge of the Bacteria and of the real existence of 
 contagia viva was in a much more advanced state, when the 
 outbreak of the epidemic in Egypt in 1883 led to a fresh re- 
 sumption of the question. R. Koch, the most experienced 
 investigator of the subject, pursued his enquiries in Egypt and 
 in India, and there became acquainted with a distinctly marked 
 Bacterium-form which is found in the intestinal canal in fresh 
 cholera-cases, and was once observed also in a water-tank in a 
 cholera-district. This Bacterium he suspected to be the specific 
 contagium or miasma of the Indian pestilence ; we will for the 
 present call it a Spirillum. 
 
 According to the facts as at present known, there can scarcely 
 be a doubt that Koch's Spirillum is really the contagium vivum 
 of Asiatic cholera. First of all, its constant presence for we 
 may call it constant in the small intestine or in the evacuations 
 of cholera-patients is acknowledged by all observers, even by 
 those who do not accept Koch's views. It is sometimes found 
 almost as in the state of a pure culture in the mucus of the in- 
 testine in bodies examined immediately after death ; under other 
 circumstances certainly it is less pure and abundant. In the 
 exceptional cases in which it was not found, either strict search 
 was confessedly not made, or it may have been overlooked or 
 have actually disappeared, especially at an advanced stage of the 
 disease, and therefore have once been present. Koch's Spirillum 
 has never been found either in the intestinal canal or in any 
 other part of the body in any disease except Asiatic cholera. 
 
 The Spirillum of cholera can readily be cultivated pure as a 
 saprophyte, as will be noticed again further on. Attempts to 
 inoculate animals with pure living material of this kind gave at 
 first only negative or in the most favourable case uncertain 
 results, and this is especially true with regard to the experiments 
 in which it was sought to convey infection with the food. It was 
 found that the Spirilla were killed by the acid gastric juice, or 
 were rendered inoperative by some other causes. But a change 
 in the mode of conducting the experiment led to a positive result. 
 
$xm.] Asiatic cholera. 161 
 
 Nicati and Rietsch and van Ermengem avoided the passage of 
 the stomach and introduced the Spirillum by injection directly 
 into the small intestine. In van Ermengem's experiments the 
 Spirillum, which had been cultivated in meat-broth or serum, 
 was injected into the duodenum of some guinea-pigs, eleven in 
 number, in small quantities, a single drop or a much smaller 
 portion of the fluid. Of the eleven, one died soon after the 
 operation, nine in two to six days after infection ; the eleventh, 
 which had received ' about one-fiftieth of a drop/ recovered after 
 a short illness. 
 
 The phenomena of the disease and the state of things as 
 shown by dissection corresponded, according to van Ermen- 
 gem's account, in all essential particulars with those of Asiatic 
 cholera, making the necessary allowance for the difference 
 between the human being and a guinea-pig. The Spirillum 
 vegetated abundantly in every case in the intestine of the infected 
 animal, either pure or mixed with other Bacteria. A drop of 
 fluid containing the Spirillum from the intestine of the animal, 
 communicated the same form of disease to sound animals when 
 injected into their duodenum. Lastly, when fluids containing 
 other Bacteria were injected into the duodenum as a test- 
 experiment, no cholera-symptoms appeared, and usually no dis- 
 turbance of the ordinary health. 
 
 I have here put these experiments in the front place, because 
 they could be most simply and briefly described. Other ob- 
 servers, Koch especially and Doyen, obtained the same positive 
 result by introducing the Spirilla with food after the acidity of 
 the contents of the stomach had been neutralised by an alkaline 
 fluid, and further by increasing the predisposition of the animals 
 for the infection by administering opium and alcohol, in accord- 
 ance with an observation of Koch's. I must limit myself here 
 to these few remarks in proof of the success of the attempts to 
 communicate the infection, and refer to the special literature for 
 further details. 
 
 It appears from the accounts which we possess that the 
 
 M 
 
1 62 Lectures on Bacteria. [ xm. 
 
 Spirillum of cholera vegetates invariably in the intestine of 
 the patient, both in the mucus of the intestine and also, according 
 to some observers, penetrating into the tissue of the mucous 
 membrane. Neither it nor any other Bacteria are found in other 
 organs of those who have died of the disease, according to Koch 
 and most other observers. But Doyen attests its presence in 
 kidneys and liver, and van Ermengem found it in the blood- 
 channel of three of the animals in his experiment before or 
 immediately after death. 
 
 On the strength of the observation that the Spirillum occurs 
 only in the intestinal canal, Koch's view is very generally thought 
 to be highly probable, that it produces a very powerful poison 
 there, and that it is this poison which being absorbed from 
 the intestine causes the severe general symptoms of cholera. 
 If it should be proved that the Spirillum is carried through the 
 body with the flow of blood, this assumption must at least receive 
 some modification, and in any case it still requires more distinct 
 proof. 
 
 As regards its shape, Koch's cholera-contagium appears, 
 when its segmentation is most perfect, in the form of spirally- 
 twisted rods or filaments, closely resembling the Spirilla 
 figured on page 82, and of very unequal length and number of 
 spirals. The filament is about 0-5 \i in thickness, but it is not 
 possible to give the exact measurement ; the width of the turns 
 of the spiral is about the same as the thickness of the filament, 
 or less ; the steepness of the individual turns varies. The fila- 
 ment is composed of segments or segment-cells, which are about 
 as long as a half-turn of the spiral, and each of them, therefore, 
 is a more or less curved rod. A separation of the segments 
 from one another does actually and as a rule take place soon 
 after every division, if the Spirillum is actively vegetating in 
 a gelatinous nutrient substratum (gelatine, agar) or on the 
 mucous membrane of the intestine ; in these places, therefore, 
 the Bacterium takes the form of crooked rods, which are either 
 single or united together into short rows; the shape of these 
 
$ XIIL] Asiatic cholera. 163 
 
 rods was naturally compared by Koch to that of a comma, and 
 he therefore called them comma-rods, comma-bacilli. In good 
 nutrient solutions, such as meat-broth, and in old gelatine 
 cultures, the segments more frequently remain united together 
 into long unbroken and apparently unsegmented spirals. In 
 both forms the Spirillum has the power of movement, the single 
 rods being more active than the longer spiral filaments, especially 
 when they have grown in old gelatine- cultures. 
 
 Hueppe has observed in old cultures a further phenomenon, 
 which must be termed spore-formation, the formation in fact 
 of arthrospores. The spiral filaments, beginning at intercalary 
 spots, divide for a certain distance into spherical segments, 
 which are a little thicker than the vegetating cells, are more 
 highly refringent, and are separated or held together by thinner 
 gelatinous envelopes. In this form they do not divide, but if 
 supplied with fresh nutriment they may at a later period 
 develope again into comma-rods, and by so doing they justify 
 their claim to be called spores. Spores of this kind appear to 
 have been seen, but not rightly understood, by former ob- 
 servers. They are quite distinct from the formations described 
 by Ferran. These are to be seen when spiral filaments in old 
 cultures swell up irregularly and shapelessly, or form round 
 bladders at their extremities, and then, as later observers have 
 unanimously declared, die off and disappear. They are con- 
 nected, therefore, simply with the retrogressive or involution- 
 forms common among Bacteria, and noticed above on page 10. 
 Ferran's sensational descriptions of these objects are inconceiv- 
 able to every sensible man with any pretension to a scientific 
 education. They have no other significance than that of a 
 warning example of the follies a man may commit, when he is 
 bent on making faulty observations seem important to himself 
 and others by the use of names and technical expressions which 
 he does not understand. 
 
 With respect to the biological characters of the Spirillum of 
 cholera, it is no longer needful from the accounts which we 
 
 M 2 
 
164 Lectures on Bacteria. [$ xm. 
 
 have of it to refer expressly to its facultative saprophytism. Its 
 saprophytic vegetation requires an abundant supply of oxygen. 
 If cultivated with this upon a suitable moist substratum it 
 developes rapidly and copiously, taking the place of any com- 
 petitors it may encounter ; but after some days the energy of its 
 growth rapidly diminishes, perhaps in consequence of the dis- 
 turbing influence of its own decomposition-products. These 
 phenomena were most strikingly exhibited in cultures on moist 
 linen, which was selected for practical reasons. The optimum 
 temperature for vegetation is, as was stated above on page 50, 
 that of the body of a warm-blooded animal, about 37 C., but 
 20-25 C. is sufficient for good development. Death ensues 
 without fail in a fluid heated to 50-55 C. The Spirillum is 
 not killed by being cooled to or below the freezing point, even 
 if this temperature is maintained some hours. Perfect desic- 
 cation kills the vegetating Spirillum in less than twenty-four 
 hours ; the arthrosporous Spirilla on the contrary, according to 
 Hueppe's direct observation, continue capable of germination 
 for four weeks after desiccation. On the other hand, as it is a 
 matter of observation that new vigorously vegetating generations 
 may proceed from desiccated cultures after a longer period than 
 this, and for almost ten months, Hueppe suspects, on good 
 though not quite conclusive grounds, that the new growths 
 always spring from arthrosporous Spirilla, and that these are 
 the specifically resistent resting states of the Bacterium of 
 cholera. I have already said all that is here necessary con- 
 cerning the food-requirements of the Spirillum, and on the 
 unfavourable or even fatal effect upon it of the acid reaction of 
 the substratum. 
 
 The phenomena in the life of the Spirillum, which have now 
 been described, supply the needful explanation of the chief facts of 
 experience in connection with cholera as an infectious disease, 
 especially its claim to be indigenous in India, its introduction 
 into other countries and parts of the globe, and the chief points 
 in the history of its diffusion there. It is true that something 
 
$ xiii.] Asiatic cholera. 165 
 
 still remains unexplained ; for instance, the immunity enjoyed 
 by certain localities, the fact that an epidemic of the disease in 
 Europe ceases entirely after the lapse of a certain time, and 
 some other points. But it is no objection to well-established 
 explanations, either here or in any other domain of human 
 knowledge, that this or that point is still unexplained. 
 
 Other objections, current certainly till quite recent times, were 
 aimed directly at the real character of Koch's Spirillum as the 
 specific contagium of cholera. So far as they rested on the 
 failure of attempts to communicate the infection with the pure 
 Spirillum, they are set aside by the positive results now before 
 us of similar attempts, supposing these to be trustworthy. On 
 the other hand, they denied that Koch's organism was present 
 exclusively in cases of Asiatic cholera. Finkler and Prior dis- 
 covered a Spirillum extremely like it in the affection of the bowels 
 known as indigenous cholera, cholera nostras. Lewis and, after 
 him, Klein pointed to the comma-spirillum of the mucus of 
 the mouth (see page 120 and Fig. 1 6, d), which is common in 
 healthy human beings, and when seen in single specimens is also 
 so like Koch's Spirillum that it might be considered to be identical. 
 But further investigation has now removed all doubt concerning 
 certain trustworthy distinctions, which come to light especially in 
 cultures on a large scale, between these and other similar forms 
 which cannot be enumerated here and Koch's organism; all 
 attempts even to cultivate Lewis' Spirillum from the mouth as a 
 saprophyte have as yet been attended with no positive result. 
 Whether Finkler's and Prior's Spirillum may be the specific 
 exciting cause of some other disease than Asiatic cholera cannot 
 be considered here. 
 
 The most thorough-going objection, however, is that brought 
 forward by Emmerich and supported by H. Buchner; these 
 observers maintain that another than Koch's Bacterium is the 
 specific contagium of cholera a short non-motile rod-bac- 
 terium, which figures in literature under the provisional name 
 of the Naples Bacillus. 
 
1 66 Lectures on Bacteria. [$ xm. 
 
 Emmerich found his Bacterium in the gelatine- cultures which 
 he employed in the examination of the bodies of persons who 
 had died of cholera in Naples; fresh bits of the wall of the 
 intestine, of the kidneys, and of other internal organs, together 
 with blood from persons who had died of the disease or who 
 were suffering from it, were placed with every precaution in the 
 nutrient gelatine. The presence of the Bacterium in the above 
 organs was concluded from the results of the culture ; it grew in 
 the culture, but it was not directly proved to have been present 
 in the organs. The result of researches undertaken a year later 
 in Palermo was, that no Bacterium could be shown to be present 
 in the internal organs, liver, spleen, kidneys, or in the heart's 
 blood in the majority of acute cholera-cases, nor was it found in 
 the viscid exudation of the peritoneal cavity. In one case only 
 was the Naples Bacillus obtained by culture from the liver of a 
 patient. But it was now found in most cases in abundance in 
 the contents of the stomach and intestine, though it must be 
 added that there was some doubt as to the identity of the forms, 
 and the decision on this point is reserved for further study. 
 Moreover, the Naples Bacillus was obtained plentifully in most 
 cases from the bronchial tubes and lungs. On the other hand, 
 Emmerich and Buchner both bear witness to the practically 
 constant presence of Koch's Spirillum in the intestine in the 
 cases which they examined. 
 
 Emmerich also experimented on animals by inoculating them 
 with pure material of his Bacillus, and obtained in this way 
 positive results, the sickening with indubitable cholera-symptoms. 
 But symptoms of this kind appear, as Virchow pointed out at 
 the second Berlin Conference on cholera, when animals are 
 inoculated with the most various kinds of substances which are 
 putrid or contain Bacteria ; they cannot therefore by themselves 
 be regarded as decisive. It is true that this objection may also 
 be made to the positive results mentioned above of infection with 
 Koch's Spirillum. But all reported observations and results of 
 experiment, the observations even of Koch's opponents, do at 
 
xiu.] Traiimatic infectious diseases. 167 
 
 present agree in attesting the significance of his Bacillus as the 
 specific contagium of cholera. Emmerich's results from Naples 
 and Palermo, on the other hand, are not consistent with those 
 of any other observer or with themselves; this detracts from 
 the value of his experimental results in view of Virchow's 
 observations. From the material before us the unprejudiced 
 critic cannot, in my judgment, find any valid objection to the 
 views of Koch and his school. 
 
 6. Among the diseases due to the action of Bacteria must be 
 reckoned also traumatic infectious diseases, with their great 
 variety of characteristic symptoms, affections also incident to 
 child-bearing, and others connected with the formation of groups 
 of ulcers, of abscesses of the skin and of the internal organs, of 
 local skin-abscesses, boils, and ulcers, as well as more serious 
 maladies (62). In these affections Bacteria-forms are found on 
 the infected surfaces of the wounds, in pus, &c., and in all but a 
 few cases, which for some special reasons are of an exceptional 
 nature ; and the eminent success of the antiseptic treatment of 
 wounds introduced by Lister, the object of which is to pre- 
 vent the approach of the organisms which set up decompo- 
 sition, and to render them harmless, is an indirect proof 
 according to our present views that these forms, as promoters 
 of decomposition, are in causal connection with the affections in 
 question. 
 
 This connection may be of two kinds. The contagium may 
 cause local suppuration, formation of abscesses, &c., at the spot 
 where it is found, either remaining in the wound which received 
 it, or passing from it into the blood and with the blood into 
 remote organs ; or else unorganised poisonous bodies, ptomaines 
 (see page 1 40), or similar substances are formed at the points of 
 infection, as products of the vegetation of the contagium, and are 
 then distributed in the blood and conveyed into the body, pro- 
 ducing symptoms of poisoning in it. It is also conceivable that 
 these two fundamentally distinct processes may occur in com- 
 bination. 
 
1 68 Lectures on Bacteria. [ xm. 
 
 This subject can only be thus briefly noticed here; the details 
 will be found in the extensive medical literature on the subject 
 with which I am myself only imperfectly acquainted. I have 
 chiefly followed Rosenbach's work, cited in note 62, on the con- 
 tagia of traumatic infectious diseases. I will only add one 
 remark, that a very noteworthy series of recent experiments are 
 now offered for our study, in which inflammation, it is true, but 
 no suppuration was caused by the application of the strongest 
 chemical irritants of very different kinds, when the co-operation of 
 Bacteria was excluded; Passet has however raised objections 
 to the universal application of this principle. 
 
 As regards the Bacteria themselves of which we are speaking, 
 several kinds have been observed. Rosenbach alone speaks of 
 four different Bacilli or at least rod-forms, and especially of 
 Micrococci, three kinds of which are common ; the others need 
 not be noticed here. The individual Micrococci cannot be 
 certainly distinguished under the microscope ; they are minute 
 round bodies with a swarming movement only, and show no 
 distinct formation of spores; but they are known from one 
 another by their appearance when grouped together, and by the 
 form and colour in which they show themselves in cultures on 
 the large scale on the surface of agar-jelly. One genus which 
 Billroth has named Streptococcus, has its cells united together 
 in rows, in the manner of Micrococcus Ureae (see page 84). In 
 the others the cells separate from the rows after division, and 
 form aggregations which Ogston has compared with a bunch 
 of grapes, and he has expressed the resemblance by the name 
 Staphylococcus. One species of Staphylococcus forms orange- 
 yellow, another white gelatinous expansions like the thallus of a 
 Lichen on agar-jelly, and they are therefore known as Staphy- 
 lococcus aureus and S. albus. If removed from abscesses and 
 collections of pus and isolated in a pure culture, each of 
 these Micrococci retains its characteristics unchanged ; some- 
 times only one species occurs in these products of disease, 
 sometimes the two are found together ; from the accounts before 
 
xiii.] Erysipelas. Trachoma. 169 
 
 us it would seem that Streptococcus and Staphylococcus aureus 
 are the most common and the most destructive kinds. Rosen- 
 bach obtained positive results from inoculations and injections 
 of pure culture-material obtained from men in several experi- 
 ments on animals, that is, the introduction of the parasite caused 
 fresh abscesses, though, if I rightly understand the accounts, 
 large quantities of matter were employed in inoculation. 
 
 The above Bacilli and Micrococci are facultative parasites, 
 and may be cultivated as saprophytes without difficulty and in 
 abundance. No details are known with respect to their diffusion 
 as saprophytes in nature, but experience of a more general kind 
 makes it probable that these formidable foes exist everywhere, 
 and especially in places of human resort; Passet has in fact 
 found two of them (Staphylococcus aureus and S. albus) in 
 dish-water and in putrid meat. 
 
 7. The Micrococcus which makes its way into the lymphatic 
 ducts of the skin and is the contagium of erysipelas (63) is 
 closely allied in respect of its shape and facultative parasitism 
 to the forms of the preceding section, and is in effect a chain- 
 forming Streptococcus. We owe our earlier knowledge of this 
 organism to von Recklinghausen and Lukomski. Fehleisen 
 has recently grown it in a pure state, and his inoculations with 
 it were successful. The unpleasant though not dangerous 
 affection of the skin of the hands, known as erythema migrans 
 or finger-erysipelas, to which those are liable who have to 
 handle raw meat, has been referred by Rosenbach to a Micro- 
 coccus (62). 
 
 8. A distinct species of Micrococcus, capable of cultivation 
 and of being conveyed by inoculation with production of the 
 characteristic disease is according to Sattler's investigation (64) 
 the contagium of trachoma, the granulose inflammation of the 
 conjunctiva of the human eye. It may be added that another 
 disease of the conjunctiva of the eye, xerosis conjunctivae, is 
 attributed to a small rod-bacterium as its exciting cause (65). 
 
 A Micrococcus forming short rows of cells in thick broad 
 
1 70 Lectures on Bacteria. [$ xm. 
 
 gelatinous envelopes, and capable of cultivation in its character- 
 istic form on gelatine, is said by Friedlander to have a strictly 
 specific effect as the contagium of acute fibrinous pneumonia 
 (66). 
 
 A specifically distinct Bacillus, nearly allied in every respect to 
 the Bacillus of tubercle, has been proved by Hansen's and 
 Neisser's investigations to be the exciting cause of leprosy in the 
 human species. The Bacillus discovered by Lustgarten, and 
 supposed to be the contagium of syphilis, is still a subject of 
 dispute (67). Other species of Bacilli, or at least of rod-forms, 
 approaching in their mode of life the Bacillus of anthrax, have 
 moreover been discovered, and many of them carefully studied 
 as the contagia of a series of diseases in the lower animals, such 
 as Koch's mouse-septicaemia, Koch and Gaffky's malignant 
 oedema (68), glanders (69), symptomatic anthrax (70), ery- 
 sipelas in pigs (71), and Loffler's diphtheria in pigeons and in 
 calves (74). 
 
 9. The type of miasmatic infectious diseases is malaria, 
 intermittent fever with its kindred states (72). The infection is 
 confined to certain localities with a marshy soil and stagnant 
 water, and is not usually conveyed from one person to another. 
 It is natural to assume therefore, in accordance with other well- 
 known cases, that of anthrax for example, that an organism is 
 present in the soil and in the water of the malaria-district, and 
 that it causes the infection. Klebs and Tommasi Crudeli have 
 consequently examined specimens of soil and water from localities 
 where malaria abounds, and have found Bacteria in them in pro- 
 fusion, one especially, a rod-shaped species which forms filaments 
 and which theyname Bacillus Malariae. Theyproduced symptoms 
 of malarial fever, swelling of the spleen and intermittent fever in 
 different animals by injecting the Bacillus from these specimens 
 of the soil as well as from cultures. Cuboni and Marchiafava, 
 Lanzi, Perroncito, Cect, and Ziehl have found Bacteria in blood 
 taken from the skin, veins, and spleen of persons suffering from 
 intermittent fever, especially in the cold stage of the attack. 
 
xiii.] Malaria. Typhoid fever. 171 
 
 Cuboni and Marchiafava have obtained in animals, into which 
 they had injected the blood of persons suffering from inter- 
 mittent fever, symptoms which they considered to be those of 
 malaria-infection. I am not in a position to say how far these 
 symptoms observed in animals after infection may, or ought to 
 be regarded as sure signs of the presence of malarial fever. 
 
 On the other hand it is obvious that the injection of some 
 cubic centimetres of fluid containing particles of soil or of a 
 Bacillus-culture does not really correspond to an ordinary in- 
 fection, in which a very minute portion of the contagium is in 
 every case absorbed, introduced by inoculation or inhaled. 
 And with respect to the descriptions given in the different pub- 
 lications of the Bacteria which were examined, we cannot be 
 sure whether one species of Bacterium was present in each case 
 or more than one, or whether the forms which one observer saw 
 in the blood were the same or of the same species as those 
 which others grew from soil-specimens. It therefore does not 
 seem to me that we have before us any precise determination of 
 the nature of the contagium or miasma vivum of malaria, but 
 that the question has now to be really attacked on the basis of 
 the former laborious investigations and with careful sifting of 
 their results. That these remarks, which appeared in the first 
 German edition of this book, were not without good foundation 
 is shown by the latest reports, especially those of Marchiafava 
 and Celli, in which it is stated that the contagium of malaria 
 is not a Bacterium, but a small amoeboid organism which 
 penetrates into the red blood-corpuscles. We must hope for 
 clear and decisive investigations into this organism. 
 
 10. Our knowledge concerning the causal connection between 
 Bacteria or parasites generally, and typhoid fever and diphtheria 
 in men is also at present uncertain, notwithstanding Gaffky's 
 and Loftier' s model investigations. 
 
 Typhoid fever is a distinctly miasmatic infectious disease, 
 which may sometimes become contagious. Causal relations 
 between its appearance and certain localities and the use of 
 
172 Lectures on Bacteria. [ xm. 
 
 impure water have long been clearly established. It is natural, 
 therefore, as in the previous case, to suppose that a facultative 
 parasite is the proximate cause of the disease. As early as 1871 
 von Recklinghausen found Bacteria, and especially colonies of 
 Micrococcus, in the bodies of those who had died of this fever. 
 Later investigations, given at length in Gaffky's publication (73), 
 have resulted in reports of the occurrence of Bacteria and Fungi 
 which do not always agree with one another. Gaffky has recently 
 undertaken a thorough investigation of the subject, and has found 
 in the internal organs, the mesenteric glands, spleen, liver, and 
 kidneys of persons who have died of typhoid fever, as an almost 
 constant phenomenon in twenty-six out of twenty-eight cases, 
 a well- characterised endosporous Bacillus, and always the same 
 kind. This species grows in characteristic form and abundantly 
 on gelatine and blood-serum, and on potatoes exposed to the air. 
 Gaffky, whose work should be consulted, states that in shape 
 it is not unlike Bacillus Amylobacter (see page 100), but con- 
 siderably smaller in size; each rod is about 2-5^ in length, and 
 the breadth is about one-third of the length. Contrary to the 
 expectations which were justified by the unfailing and character- 
 istic presence of the Bacteria in the bodies of the dead, Gaffky's 
 extensive experiments in the infection of animals, and among 
 them of monkeys, gave wholly negative results. The question 
 of cause must therefore be considered to be at present undecided. 
 How far more recent accounts of successful experiments of this 
 kind will avail to alter this judgment I am not yet able to deter- 
 mine. It has also not yet been proved that the Bacilli of typhoid 
 fever occur spontaneously outside the organism, especially in 
 the water for drinking and for domestic use which is connected 
 with epidemics of the fever. 
 
 ii. We are indebted to Loffler (74) for extended and careful 
 investigations into the nature of diphtheria. His work contains 
 a detailed discussion of the statements of his predecessors, and 
 should therefore be consulted. One well-known and character- 
 istic symptom of diphtheria in the human subject is the forma- 
 
$ xiii.] Diphtheria. 173 
 
 tion of the white lining on the mucous membrane of the throat, 
 especially on the tonsils, and it has been proved that by means 
 of this lining the disease can be communicated to a healthy person. 
 Enquiry was accordingly directed to this substance, and it was 
 found to contain, along with a variety of accidental matters, first 
 of all enormous accumulations of Micrococci, and secondly, small 
 rods in many of the cases which were examined, but not in all of 
 them, as was at first maintained by Klebs. 
 
 Loftier having ascertained the presence of these organisms 
 subjected them to pure culture, and made experimental trial of 
 their efficacy in the production of disease. 
 
 The Micrococcus in a pure culture forms chains which are 
 very like those of erysipelas. It forces its way from the diphtheritic 
 lining on the mucous membrane into the tissues of a person 
 suffering from the disease, and passes through the lymph-vessels 
 into the most dissimilar internal organs, where it forms nests. 
 It behaved in a similar manner when introduced in the pure 
 state into animals by inoculation, and produced some forms of 
 disease, but did not give rise to the symptoms characteristic of 
 diphtheria. We may therefore ascribe to this Micrococcus the 
 power of producing morbid complications, but we cannot accept 
 it as the specific contagium of diphtheria. 
 
 The rods thrive well on blood-serum, but are difficult of 
 cultivation in other substrata. They are about as long as those 
 of the Bacillus of tubercle and twice as thick, and are otherwise 
 distinguished from this species by marks which cannot be fully 
 described here. They are found collected together in heaps in 
 the lining of the diphtheritic mucous membrane, in the layers 
 beneath the surface. They have not been observed in the in- 
 ternal organs of sick persons. Introduced by inoculation into 
 animals of the kinds usually employed for experiment, they 
 produced symptoms very like those of diphtheria. LorBer there- 
 fore considers that the rods are the contagium of diphtheria in 
 the human subject, though he is careful to draw attention to the 
 objections to this conclusion. 
 
1 74 Lectures on Bacteria. [$ xiv. 
 
 12. In conclusion we must not omit to remark, that in a 
 large number of infectious diseases, and these too of the most 
 common occurrence, no one has as yet succeeded in discovering 
 a distinct Bacterium or any other microscopic parasite as the 
 cause of the particular disease, or the supposed discovery of 
 such organisms is quite untrustworthy. This is true of diarrhoea, 
 of typhus fever, of yellow fever, of whooping-cough, and of 
 acute exanthemata of the skin, such as scarlet fever, measles, 
 and small-pox in men and equivalent diseases in other animals. 
 We practise vaccination, as is well known, as a protection 
 against small-pox, and Pasteur applies his famous method for 
 attenuating the contagium of hydrophobia, for protective inocu- 
 lation and for curing the infected, but the organism which may 
 possibly be the real contagium has hitherto at least escaped 
 observation. It is not really necessary to repeat that Henle's 
 postulates remain unchanged as against these negative results 
 in the search for the contagium vivum. 
 
 XIV. 
 
 Diseases caused by Bacteria in the lower animals 
 and in plants. 
 
 i. THERE is reason for assuming that Bacteria play a more 
 important part as disease-producing parasites in cold-blooded 
 as well as in warm-blooded animals, than is at present ascer- 
 tained. What we do know at present is chiefly connected with 
 insects (76). 
 
 The foul brood in bees, which may in a short time destroy 
 the hives of a whole district, is the work of an (endosporous) 
 Bacillus, B. melittophthorus, Cohn, in all probability the same 
 species as B. alvei, which has been carefully studied by Cheshire 
 and Cheyne. 
 
 The disease in silkworms known as flacherie is caused, 
 
$ xiv.] Diseases in lower animals. 175 
 
 according to Pasteur, by a Bacillus and by a chain-forming 
 Micrococcus, M. Bombycis, Cohn, which resembles M. Ureae 
 (see page 84) ; these organisms are introduced with the food, and 
 by decomposing it in the intestinal canal give rise first of all to 
 derangement of the digestion, and then to the death of the insect, 
 which first becomes inert, without appetite, and flabby, and soon 
 succumbs to the disease. Its dead body is soft and soon turns 
 a dark and dirty brown, putrefactive Bacteria make their ap- 
 pearance in it and it dissolves for the most part into discoloured 
 stinking matter. 
 
 A number of other contagious and epidemic diseases in cater- 
 pillars of Lepidoptera have been recently referred by S. A. Forbes 
 to the attacks of certain forms of Micrococcus and Bacillus. 
 
 There are two diseases among silkworms very distinct from 
 the flacherie, which is the prevalent one at the present time, 
 namely, muscardine or calcino, and the spotted disease or 
 pe'brine. Muscardine, known since the last century, was very 
 destructive to the silkworm-culture in Europe during the first 
 years of the present century, but is said to have almost entirely 
 disappeared since 1855, while it continues to be of frequent 
 occurrence among the caterpillars living in the wild state. It is 
 caused, as has been fully shown, by a Fungus, and does not 
 therefore belong to our present subject. 
 
 Pebrine (gattine, petechia, maladie des corpuscules) has been 
 a known form of disease for some hundreds of years, and com- 
 mitted great ravages in Europe between 1850 and 1875. It 
 received the name of spotted disease from the dark spots on 
 the skin which make their appearance in the insect as it becomes 
 dull and inert, and which are caused by the presence of a micro- 
 scopic parasite, Panhistophyton ovatum, Lebert, Nosema Bom- 
 bycis, Nageli. The parasite is known under the form of small 
 colourless, highly refringent bodies of irregularly ellipsoid 
 shape, and not more than 0-4 /z in length, once termed the Cor- 
 nalian bodies, which appear in our preparations either singly, 
 or in pairs, or several connected together, and occur in all organs 
 
176 Lectures on Bacteria. [$ xiv. 
 
 of the creature, and not in the caterpillar only, but also in the 
 butterfly and even in the eggs, from which they may find their 
 way again into the young caterpillar. They are also found in 
 enormous quantities, filling the entire insect. Pasteur especially 
 has shown that these bodies belong to a parasite, which 
 penetrates into the insect, and multiplying at its expense pro- 
 duce the disease. If they are introduced with the food into the 
 intestinal canal of a healthy caterpillar, they are subsequently 
 found to have penetrated into the wall of the intestine, at first 
 one by one, afterwards in greater numbers, and to have spread 
 from thence into the other organs. 
 
 The same or similar bodies have been found by different 
 observers in sundry other insects and articulated animals. 
 
 It would appear from this brief description that the Cornalian 
 bodies resemble a small Bacterium, and specially a Micro- 
 coccus, and they have been regarded as such by many observers. 
 Nageli calls attention in his first communication to their relation- 
 ship to Micrococcus aceti. This view rested on the similarity 
 of form, and specially on the observation that they were frequently 
 united together in pairs, since this fact was regarded as an indi- 
 cation of their multiplication by successive bipartition. Their 
 bipartition was not directly observed at that time nor has it been 
 observed subsequently, and it is obvious that union in pairs may 
 be brought about in other ways. There was therefore experi- 
 mental proof that the bodies did multiply, but how they multi- 
 plied was not known. Then Cornalia, Leydig, Balbiani, and 
 also Pasteur put forward another view in opposition to the theory 
 that the bodies were Micrococci; they supposed them to be 
 totally distinct from Micrococcus and Bacterium, and to be 
 Psorospermiae, that is, states of peculiar low organisms, 
 Sporozoa or Sarcosporidia. Metschnikoff has recently and 
 distinctly confirmed this view; he states briefly that the 
 parasite of pe*brine consists of protoplasmic bodies having the 
 power of amoeboid movement, after the manner, that is, of the 
 colourless blood-cells described on page 135, and subsequently 
 
xiv.] Diseases in lower animals and in plants. 177 
 
 becoming lobed, and that the Cornalian bodies are produced in 
 them by endogenous formation. It follows from analogy with 
 other better-known Sporozoa, that the Cornalian bodies would 
 be spores, and that their germination gives rise to the amoeboid 
 protoplasmic bodies in which fresh spores are formed in large 
 numbers. The extreme delicacy of such amoeboid protoplasmic 
 bodies as these sufficiently explains why it was so long before 
 they were clearly made out, especially when they had penetrated 
 into and were enclosed in the tissue of the insect's body which 
 is also protoplasmic. 
 
 Hence the parasite of pe*brine must also be excluded from 
 consideration in a treatise on Bacteria; nor would so much 
 have been said about it here, if it did not serve to show in a 
 very instructive manner, not only that very minute parasites 
 which are not Bacteria are the contagium in infectious diseases 
 in animals, but that we may be dealing with organisms of a quite 
 different kind, conformation, and mode of life from Bacteria, 
 even when the figures before us are very like Bacteria and are 
 easily mistaken for them. 
 
 2. Lastly, parasitic Bacteria do not often appear, according 
 to our present experience, as the'contagia of diseases in plants (77). 
 Most contagia of the many infectious diseases in plants belong 
 to other groups of animals and plants, the larger number to the 
 Fungi proper, as was observed on pages 146, 147. 
 
 Among cases of the kind we may mention first the yellow 
 disease studied by Wakker, which destroys hyacinth-plants. 
 Wakker found that the most characteristic symptom in this 
 disease is the appearance of a rod-shaped Bacterium, 2-5 //, long 
 and a fourth or half as broad, which aggregates into slimy yellow 
 masses filling the vessels and tissue of the vascular bundles 
 in the bulb-scales during the time when vegetation is dormant. 
 At flowering time these masses ascend also into the leaves, 
 where they are not confined to the vascular bundles, but make 
 their way from them into the intercellular passages and into the 
 cells of the parenchyma, stopping up the passages and destroying 
 
178 Lectures on Bacteria. [ xiv. 
 
 the cells, and ultimately emerging through the bursting epi- 
 dermis. Attempts to communicate the disease by inoculation 
 have not yet been successful, nor has the life-history of the 
 Bacterium been at present thoroughly worked out. 
 
 J. Burrill, of Urbana, in the state of Illinois, describes a 
 disease in pear-trees and apple-trees, known by the indefinite 
 name of 'blight/ and attributes it to the attack of a 
 Bacterium, a rather elongated Micrococcus, M. amylovorus, 
 Burr., the cells of which are about i /z in length. The disease, 
 which destroys the bark, is at first narrowly localised, but may 
 spread and form a ring round the branch or stem which it 
 attacks, and may then prove fatal to it. Burrill found that the 
 Micrococcus had penetrated into the cells of the diseased part, 
 and that as it developed the normal contents of the cells, 
 especially the starch, disappeared, while ' carbonic acid, hydrogen 
 and butyric acid' were formed. Numerous attempts at inoculation 
 by introducing the Micrococcus into small incisions or punc- 
 tures in the bark of healthy pear-trees and apple-trees resulted 
 in the communication of the disease. Arthur has confirmed 
 Burrill's observations and given further proof that his Micro- 
 coccus is a facultative parasite, producing effects peculiar to 
 the species. This disease of pear-trees, as far as I am aware, 
 is either unknown in Europe, or has not been investigated. 
 
 From some very brief statements of Burrill it would appear 
 that diseases caused by Bacteria also occur in the peach-tree, 
 the Italian poplar, and the American aspen. 
 
 Prillieux gives a short description of a change which some- 
 times takes place in grains of wheat ; this change which is recog- 
 nised by the rose-red colour which it produces, advances part 
 passu with the development of a Micrococcus, which destroys 
 the starch-grains, the glutinous contents of the peripheral cell- 
 layers, and to some extent the cell-membranes as well. Dis- 
 organising operations of the Micrococcus are thus distinctly 
 disclosed. Its real significance as an exciting cause of disease 
 cannot be certainly determined from the few published state- 
 
xiv.] Diseases in plants. 1 79 
 
 ments, it may perhaps only play a secondary part as a saprophyte 
 in consequence of injuries produced by other causes. 
 
 The latter supposition is partly founded on the phenomenon 
 of wet rot in potatoes, which has been closely examined by 
 Reinke and Berthold. It appears from the observations of 
 these authors, that the proximate cause of the phenomenon is 
 the development of Bacteria ; Bacillus Amylobacter is shown by 
 the descriptions to be present, and perhaps some other forms. 
 The wet rot usually attacks tubers which have been previously 
 sickly, that is, have been partly destroyed by a purely parasitic 
 Fungus, Phytophthora infestans. The rot does indeed attack 
 the tissue which had been spared by the Fungus and is still 
 alive, but it nevertheless is only a secondary phenomenon. At 
 the same time the rot appears in potatoes which have not suffered 
 from Phytophthora, though this is exceptional ; and the above- 
 mentioned observers succeeded in producing wet rot in healthy 
 potato-tubers by inoculating them with their Bacteria. This 
 agrees with a recent experiment of van Tieghem, who succeeded 
 in entirely destroying living tubers by the introduction of Bacillus 
 Amylobacter into their inner substance, and by keeping them 
 at the same time at the high temperature of 30 C. The same 
 results were obtained with the seeds of beans, stems of Cacti, &c. 
 In other words, these facts show that saprophytic Bacteria may 
 also, under special conditions, attack the tissues of living plants 
 as facultative parasites, produce disease in them and destroy 
 them. But this only confirms what was said above, that Bacteria 
 are not objects of great importance as contagia of diseases 
 affecting plants. 
 
 N 2 
 
CONSPECTUS OF THE LITERATURE 
 AND NOTES. 
 
 1. FOR the general literature of the Bacteria see de Bary, Comparative 
 Morphology and Biology of the Fungi, Mycetozoa, and Bacteria, Clarendon 
 Press, 1887, and W. Zopf, Die Spaltpilze, 3rd edition, Breslau, 1884. 
 The works of Pasteur, F. Cohn, v. Nageli, van Tieghem, R. Koch, Brefeld, 
 A. Prazmowski, Fitz, must be specially mentioned here as laying generally 
 the foundations of our knowledge ; they are cited in the works above-named, 
 and some of them again below. Duclaux, Chimie biologique, Paris, 1883, 
 gives an elegant account of the views and methods of the French school, 
 and especially of the school of Pasteur ; F. Hueppe, Die Methoden d. 
 Bacterienforschung (3rd ed., 1886), gives hints for the conduct of investigation 
 according to the method perfected especially by R. Koch. Writers on 
 General Morphology and Classification are F. Hueppe, Die Form en d. 
 Bacterien. &c., Wiesbaden, 1886; J. Schroter in the Kryptogamenflora v. 
 Schlesien, ed. F. Cohn, Bd. Ill, 2 Lieferung, pp. 136-172. This work gives 
 a good classification and description of most known forms ; it reached me 
 while the present work was in the press, and it was hardly possible for me 
 to make any use of it. Of the many general Text-books of Bacteria of 
 recent date may be mentioned : C. Fliigge, Fermente u. Mikroparasiten, in 
 v. Pettenkofer and v. Ziemssen, Handb. d. Hygieine (the second edition 
 with the title, Die Mikroorganismen, Leipsic, 1886, came out while this 
 work was being printed) ; E. M. Crookshank, Introduction to practical 
 Bacteriology, London, 1886; and a copious Text-book of the Bacteria of 
 Disease, by Cornil et Babes, Les Bacteries et leur role dans 1'anatomie et 
 1'histologie pathologiques des maladies infectieuses, 2nd ed., Paris, 1886. 
 With these may be coupled the Jahresbericht u. d. Fortschritte d. Lehre v. 
 d. pathogenen Mikroorganismen of P. Baumgarten, Erster Jahrg. 1885, 
 Braunschweig, 1886, of which I have made frequent use, and to which 
 I here refer the reader once for all for the more recent special literature. 
 
 2. Nencki u. Schaffer, Journ. f. pract. Chemie, Neue Folge, XX. 
 Nencki, Berichte d. D. Chem. Ges. Jahrg. XVII, p. 2605. 
 
 3. Leeuwenhoek, Experimenta et contemplationes, Delft, 1695, especially 
 p. 42, on Bacteria- forms from saliva. 
 
 4. F. Cohn, Unters. ii. Bacterien, in Beitr. z. Biologic d. Pfl., continued 
 since 1872 (I, Heft 2, p. 127). 
 
1 82 Lectures on Bacteria. 
 
 5. C. G. Ehrenberg, Die Infusionsthiere als vollk. Organismen, Berlin, 1838. 
 
 6. Billroth, Coccobacteria septica, Berlin, 1874. 
 
 7. v. Nageli, Die niederen Pilze, Munch en, 1877. 
 
 8. Hornschuch in Flora, Regensburg, 1848. 
 
 9. v. Nageli, Niedere Pilze, 1877, p. 21. 
 
 10. F. Hueppe, Unters. ii. d. Zersetzgn. d. Milch., in Mittheil. aus d. K. 
 Gesundheitsamt, II, 1884. 
 
 11. C. Vittadini, Delia natura del calcino, in Giorn. Istitut. Lombardo, 
 III (1852). 
 
 12. E. Klebs, Beitr. z. Kenntn. d. Mikrokokken, in Arch. f. exp. Patho- 
 logic, I (1873). 
 
 13. Pasteur, Examen de la doctrine des generations spontanees in Ann. 
 de Chimie, ser. 3, LXIV. See also Ann. d. sc. nat., Zoologie, ser. 4, XVI. 
 Rosenbach has given an account of Meissner's excellent researches in 
 Deutsche Zeitschr. f. Chirurgie, XIII, p. 344. For more recent works and 
 discussions, see in Baumgarten's Jahresber. 
 
 14. R. Koch in Mittheil. aus d. K. Gesundheitsamt, I, p. 32. See also 
 Hesse, in the same publication, II, 182. 
 
 15. Annuaire de 1'observatoire de Montsouris, since 1877, and especially 
 since 1879. 
 
 16. Virgil, Georgics, IV, 281. 
 
 17. A. Bechamp, Les Microzymas dans leurs rapports avec 1'heterogenie, 
 1'histiogenie, la physiologic et la pathologic, Paris, 1882. In this volume 
 Bechamp has brought together the views successively entertained by him 
 and published in the Comptes rendus of the Paris Academy. 
 
 18. A. Wigand, Entstehung u. Fermentwirkung d. Bacterien, Marburg, 
 1884. 
 
 19. O. Brefeld, Botan. Untersuch. ii. Schimmelpilze, IV. 
 
 20. E. Eidam in Cohn's Beitr. z. Biol. d. Pflanzen, I, Heft 3, p. 208. 
 
 21. A. Fitz in Ber. d. Deutsch. Chem. Ges., nine papers in the years 
 1876-84. 
 
 22. Frisch in Sitzungsber. d. Wien. Acad., Mai, 1877. 
 
 23. P. van Tieghem in Bull, de la Soc. Bot. de France, XXVIII (1881), 
 
 P- 35- 
 
 24. E. Duclaux, Etudes sur le lait, in Ann. de Tlnstit. Nat. Agronomique, 
 No. 5, Paris (1882), pp. 22-138. 
 
 25. E. Duclaux, Chimie biolog., in Encyclop. Chimique, publiee par M. 
 Fremy, IX, Paris, 1883. 
 
 26. W. Engelmann in Bot. Ztg., 1882, p. 321. 
 
 27. v. Nageli, Ernahrung d. niederen Pilze, in Sitzungsber. d. Miinchener 
 Acad., Juli, 1879. 
 
 28. v. Nageli, Unters. ii. niedere Pilze, in Unters. aus d. Pflanzenphysiol. 
 Inst. z. Munchen, Miinchen, 1882. 
 
 29. W. Engelmann, Bacterium photometricum, in Unters. aus d. Physiol. 
 Laboratorium z. Utrecht, 1882. 
 
Literature and Notes. 183 
 
 30. Cohn u. Mendelssohn in Beitr. z. Biol. d. Pflanzen, III. 
 
 31. W. Engelmann in Bot. Ztg., 1881, p. 441. 
 
 32. W. Pfeffer, in Unters. a. d. Bot. Inst. z. Tubingen, I, Heft 3. 
 
 33. J. Tyndall in Phil. Trans, of the Royal Soc., London, 166 (1876), 
 167 (1877). The latter paper especially contains the statements with respect 
 to fractionating sterilisation. 
 
 34. J. Wortmann in Zeitschr. f. physiol. Chemie, VI, p. 287. 
 
 35. I still keep to the classification and nomenclature founded on Cohn's 
 divisions. It is better to treat what is imperfect as imperfect than to give it 
 the appearance of being perfect, and so cheat oneself and the beginner into 
 belief in a state of things which does not really exist. This might also be 
 said in criticism of some of the most recent attempts at improvement, but 
 further discussion of these would be out of place here. We have not yet 
 accomplished that which is an indispensable condition for any real advance 
 in classification, namely, a tolerably continuous morphological examination 
 of the individual species, I do not mean of all existing species, but only of 
 such as at present pass for being ' described,' whether collective or ' bad ' 
 species. Such an examination might be made with the material which we 
 at present possess, but this has not yet been done. 
 
 36. W. Zopf, Zur Morphol. d. Spaltpflanzen, Leipsic, 1882 ; Id., Entwick- 
 lungsgeschichtl. Unters. ii. Crenothrix polyspora, die Ursache d. Berliner 
 wassercalamitat, Berlin, 1879 ; Id. in Monatsber. d. Berliner Acad., 
 Marz 10, 1881. 
 
 37. E. Warming, Om nogle ved Danmarks Kyster levende Bacterier, in 
 Vidensk. Meddelelser fra d. naturhist. Forening, Kjobenhavn, 1875. A. 
 Engler, Die Pilzvegetation d. weissen od. todten Grundes d. Kieler Bucht, 
 in Ber. d. Commiss. z. Erforschung d. deutschen Meere, IV. 
 
 38. P. van Tieghem, Sur la fermentation ammoniacale, in Compt. rend. 
 LVIII (1864), p. 211. v. Jacksch in Zeitschr. f. physiolog. Chemie, V 
 (1881), p. 395. Leube, Ueber d. ammoniakal. Harngahrung. in Virchow's 
 Archiv, C, p. 540. 
 
 39. Schlossing u. Miintz in Compt. rend. LXXXIV, p. 301 ; LXXXIX, 
 pp. 91, 1074. 
 
 40. Pasteur in Compt. rend. LIV, p. 265 ; LV, p. 28 ; Id., Etudes sur 
 le vinaigre, Paris, 1868. 
 
 41. v. Nageli, Theorie d. Gahrung, Miinchen, 1879. 
 
 42. E. C. Hansen, Beitr. z. Kenntn. d. Organismen welche, in Bier u. 
 Bierwiirze leben, in Meddelelser fra Carlsberg Laboratoriet, I, Kopenhagen, 
 1882. 
 
 43. Pasteur in Compt. rend. LII, p. 344. 
 
 44. P. van Tieghem, Leuconostoc, in Ann. d. sc. nat. ser. 6, VII. 
 
 45. F. Hueppe, Unters. ii. d. Zersetzung d. Milch durch Mikroorganismen, 
 in Mittheil. a. d. k. Reichsgesundheitsamt, II, 309, with a full account of 
 the history and literature. 
 
 46. E. Kern, Ueber ein Milchferment aus dem Kaukasus, in Bot. Ztg., 
 
1 84 
 
 Lectures on Bacteria. 
 
 1882, p. 264, and in Bullet, de la Soc. Imper. d. Nat. de Moscou, 1881. See 
 also F. Hueppe, Ueber Zersetzungen d. Milch, &c., in Borner's Deutscher 
 med. Wochenschrift, 1884, No - 48. W. Podwyssotzki (Sohn), Kefyr, kau- 
 kasisches Gahrungsferment u. Getrank, &c., translated from the Russian of 
 the 3rd Edition by Moritz Schulz, St. Petersbg., 1884. W. N. Dimitrijew, 
 Kefir oder Kapir, echtes Kumyiss aus Kuhmilch, translated from the 
 German by E. Rothmann, St. Petersbg., 1884. Alexander Levy, Die wahre 
 Natur des Kefir, in Deutsche medicinal Zeitung, 1886, p. 783. Levy's 
 manner of proceeding is to add one part of ordinary sour milk to 8-10 
 parts of cold boiled milk, and then to shake the mixture at a temperature of 
 about I2C. 
 
 47. P. van Tieghem, Sur le Bacillus Amylobacter, &c., in Bull. Soc. Bot. 
 de France, XXIV (1877), p. 128 ; Id., Sur la fermentation de la cellulose, 
 in Bull. Soc. Bot. de France, XXVI (1879), p. 25. 
 
 48. A. Prazmowski, Untersuch. ii. Entwicklungsgesch. u. Fermentwirkung 
 einiger Bacterien-Arten, Leipzig, 1880. 
 
 49. Vandevelde, Studien z. Chemie d. Bacillus subtilis, in Zeitschr. f. 
 physiolog. Chemie, VIII, 367. 
 
 50. Bienstock, Ueber d. Bacterien d. Faeces, in Zeitschr. f. klin. Medicin, 
 VIII. 
 
 51. Cohn, Beitr. I, Heft 2, p. 169. G. Hauser, Ueber Faulnissbacterien 
 u. deren Beziehung z. Septicaemie, Leipzig, 1885. I have made little use 
 of this work in the text, because I am unable sufficiently to understand its 
 morphology without personal investigation. The whole of the phenomena 
 of ' pleomorphism,' on the strength of which the writer designates his forms 
 by the special generic name Proteus, an unacceptable one in any case, 
 appear to me, on comparing the figures, scarcely to deserve the appellation. 
 But the figures do not help us in determining the morphological relations, 
 at least if we go beyond the habit of the groups ; I have taken fruitless 
 pains to arrive by their means at a clear idea of the conformation of the 
 Spirilla-forms which he describes. Photography is no doubt a useful 
 assistant in microscopical studies, and I have used it myself for twenty-five 
 years ; but there are limits to its capabilities, and the details required in this 
 case are not given in Hauser's figures. With all due acknowledgment of 
 the advance made in Hauser's work, I say what I have now said in order to 
 justify my casual treatment of it. 
 
 52. H. Nothnagel, Die normal in d. menschl. Darmentleerungen vorkom- 
 menden niedersten pflanzl. Organismen, in Zeitschr. f. klin. Medicin, III 
 (1881). Kurth, Bacterium Zopfii, in Bot. Ztg. 1883, 369. Miller, Ueber 
 Gahrungsvorgange im Verdauungstractus, &c., in Deutsche med. Wochen- 
 schrift, 1885, No. 49. W. de Bary, Beitr. z. Kenntn. d. niederen Organismen 
 im Mageninhalt, in Archiv f. experim. Pathologic u. Pharmacologie, XX. 
 
 53. The literature of Sarcina has been carefully collected by Falkenheim 
 in his paper Ueber Sarcina, published in Archiv f. experim. Pathologic, 
 XIX, p. 339. 
 
Literature and Notes. 185 
 
 The species of Sarcina which I am able to distinguish are characterised 
 as follows : 
 
 a. Sarcina ventriculi, Goodsir (see Fig. 14 of this book). Large cube- 
 shaped packets, with very many members, that is, consisting usually of 
 64-4096 cells, the single packet brownish-gray in transmitted light under 
 the microscope, of a dirty greyish-white colour when seen in mass by the 
 naked eye in reflected light. Single cells, 3-4 /* in size, stained a dirty 
 violet by Schulze's solution. 
 
 In large quantities of material from the human stomach I generally find 
 two distinct forms side by side, a large-celled one which is represented in 
 Fig. 14, and another in which the cells are smaller (2 /*) and less clearly 
 translucent. I can give no information respecting the genetic relations of 
 the two forms. 
 
 b. Sarcina Welckeri, Rossmann (Welcker in Henle's u. Pfeffer's Zeitschr. 
 f. rat. Med. V, 199). Small cube-shaped packets, containing at most 64 
 cells, quite colourless. Single cells about I p in size, membranes not 
 coloured by Schulze's solution, protoplasm coloured yellow by the same 
 solution. It occurs in the urinary bladder of the living human subject ; 
 repeatedly found in patients. I know the species as coming from a 
 young man, who, according to his own observation, voided them with the 
 urine for more than twelve months, in varying, often in very large, quanti- 
 ties. The urine is usually abnormally rich in phosphates ; the patient is in 
 other respects in good health. The Sarcina did not grow with me on 
 gelatine and agar ; once doubtfully and not in any abundance in sterilised 
 urine at a temperature of 35C. Most of the attempts to cultivate it in urine 
 gave negative results. 
 
 c. Sarcina flava. Small packets, containing from 16 to 32 cells, con- 
 nected together in the majority of cases either into large regular cubes or 
 into irregular heaps ; the single packet colourless in transmitted light under 
 the microscope, of a beautifully bright yellow colour when seen in mass in re- 
 flected light. Single cells 1-2 p in size. Reaction with iodine as in Sarcina 
 Welckeri. Grows well on gelatine, which it quickly liquefies, on agar and 
 on other substances. Appears to be comparatively abundant ; is cultivated 
 in laboratories, and described without statement as to the source from which 
 it is obtained. See Crookshank, Introd. to practical Bacteriology, London, 
 1886. My material comes from the Pathological Institute at Greifswald, 
 where the yellow Sarcina made its appearance spontaneously as an isolated 
 colony in a gelatine culture of vomited matter, in which Sarcina ventriculi 
 had not been found. It is at all events distinguished from S. lutea of 
 Schroter by its power of liquefying gelatine. 
 
 d. Sarcina minuta, provisionally a new species (see Fig. 15 of this 
 book). Small cube-shaped packets, formed of 8-16 cells, connected 
 together in the majority of cases in irregular heaps, less frequently in 
 larger cubes ; quite colourless. Single cells about i /* in size. Reactions 
 with iodine as in Sarcina Welckeri. Made its appearance once spon- 
 
1 86 Lectures on Bacteria. 
 
 taneously in a culture of sour milk on a microscopic slide. Grows well 
 but slowly on gelatine and in a saccharine solution with extract of meat, 
 forming in the solution the regular cube-shaped packets, on the gelatine the 
 irregular heaps. Closely resembling Sarcina Welckeri under the microscope. 
 
 e. Sarcina fuscescens. Small cube-shaped packets of 8-64 cells, readily 
 separating into smaller groups (tetrads) or into single cells. Single cells 
 about 1-5 p in size. Reactions with iodine as in Sarcina Welckeri. Forms 
 small brownish scales or mould-like films on the substrata mentioned 
 below. This form was obtained by Falkenheim in gelatine cultures of the 
 contents of a human stomach containing Sarcina ventriculi, with which, 
 however, there was no apparent genetic connection. It grew in connected 
 packet-form on infusion of hay ; culture on other ordinary nutrient substrata 
 (gelatine, potatoes, &c.) was accompanied by the separation mentioned above 
 into single cells and smaller cell-groups. The above description is taken 
 from Falkenheim's paper on Sarcina in Archiv f. experim. Pathologic, XIX, 
 p. 339 ; the form or species is not known to me by personal observation. 
 
 To the above must be added the distinct and described species, Sarcina 
 intestinalis, Zopf (Spaltpilze, p. 55 of the third edition), from the intestinal 
 canal of the domestic fowl ; S. lutea, Schroter (Krypt. Fl. v. Schlesien), a 
 saprophyte which makes its appearance in Fungus-cultures ; and Schroter's 
 S. rosea and S. paludosa, which live in bog-water. 
 
 Other forms, belonging apparently to the genus Sarcina, are mentioned 
 by J. Eisenberg (Patholog. Diagnostik), but they are without any special 
 description, and cannot therefore be compared with the preceding species. 
 A ' Sarcina in the mouth and lungs' has been considered by H. Fischer, in 
 the Deutsches Archiv f. klin. Medicin, XXXVI, p. 344 ; but it is not even 
 clear from his description whether the cells or divisions of cells are arranged 
 according to two or three dimensions ; we are therefore unable to compare 
 this supposed form with the rest of the species. 
 
 The names Sarcina littoralis, Oersted, S. hyalina, Kiitzing, and S. Reiten- 
 bachii, Caspary (also misprinted Reichenbachii), have been copied into the 
 literature of the Bacteria. The proximate source of these names is Winter's 
 Pilzflora v. Deutschland, &c. Merismopoedia littoralis, Rabenhorst, M. 
 hyalina, Kiitzing, M. Reitenbachii, Casp., have thus been placed in the 
 genus Sarcina ; this appears to me to be incorrect, because, as the name 
 Merismopoedia implies, the cells in accordance with the directions of their 
 divisions, form not many-layered packets, but tables of a single layer, and 
 because it is uncertain, at least in the case of the two last forms, whether, 
 like other species of Merismopoedia, M. punctata for example, they do not 
 contain chlorophyll or phycochrome. These forms, therefore, do not belong 
 to this place ; like other species of Merismopoedia they live in bogs and in 
 sea-water. 
 
 54. Rasmussen, Ueber d. Cultur v. Mikroorganismen aus d. Speichel 
 (Spyt) gesunder Menschen ; Dissert. Kopenhagen, 1883. Known to me 
 only from an abstract in the Bot. Centralblatt, 1884, XVII, p. 398. 
 
Literature and Notes. 187 
 
 55. W. Miller, Der Einfluss d. Mikroorganismen auf d. Caries d. menschl. 
 Zahne, in Archiv f. exp. Pathol. XVI, 1882; Id., Gahrungsvorgange im 
 menschlichen Munde in Beziehung zur Caries d. Zahne, &c., in Deutsch. 
 med. Wochenschrift, 1884, No. 36. T. Lewis, Memorandum on the comma- 
 shaped Bacillus, &c., in the Lancet, Sept. 2, 1884. 
 
 56. For the earlier literature of Anthrax (up to 1874) see O. Bollinger, 
 in Ziemssen's Handb. d. speciellen Pathologic u. Therapie, 3, and the rich 
 material in Oemler, Experimentelle Beitr. z. Milzbrandfrage in Archiv f. 
 Thierheilk, II-VI. For the first discovery of the Bacillus, see Rayer in 
 Memoires de la Soc. de Biol. II, 1850, p. 141 (Paris, 1851). Pollender 
 in Casper's Vierteljahrsschr. VIII, 1855. Of the very numerous works of 
 a more recent date may be mentioned : Pasteur in Compt. rend. LXXXIV 
 (1877), p. 900; LXXXV (1877), P- 99; LXXXVII (1878), p. 47; XCII 
 (1881), pp. 209, 266, 429. R. Koch, Die Aetiologie d. Milzbrandes, in 
 Cohn, Beitr. z. Biol. d. Pfl. II, 277 ; Id. in Mittheil. a. d. Reichsgesund- 
 heitsamt I, and II in conjunction with Gaffky and Loffler. H. Buchner in 
 Unters. aus d. Pflanzenphysiol. Inst. z. Miinchen, 1882. Chauveau in Compt. 
 rend. XCI (1880), p. 680; XCVI (1883), pp. 553,612, 678, 1471 ; XCVII 
 (1883), pp. 1242, 1397; XCVIII (1884), pp. 73, 126, 1232. Gibier in 
 Compt. rend. XCIV (1882), p. 1605. E. Metschnikoff, Die Beziehung d. 
 Phagocyten z. d. Milzbrand-Bacillen, in Virchow's Archiv, XCVII, 1884. 
 A. Prazmowski in Biolog. Centralblatt, 1884. 
 
 57. Pasteur in Compt. rend. XC (1880), pp. 239, 952, 1030 ; XCII (1881), 
 p. 426. Semmer, Ueber d. Hiihnerpest, in Deutsche Zeitschr. f. Thier- 
 medicin, IV (1878), p. 244. The disease described by Perroncito, in Archiv 
 f. wiss. u. pract. Thierheilk. V (1879), p. 22, must be of another kind. 
 Kitt, Exper. Beitr. z. Kenntn. d. epizootischen Geflligeltyphoids, in Jahresber. 
 d. k. Thierarzneischule in Miinchen, 1882-1884, p. 62, Leipzig, 1885. This 
 excellent work contains an exact account firstly of the form of the Micro- 
 coccus and its behaviour in cultures, and secondly of experimental investiga- 
 tions into infection and the phenomena of the disease which follows upon the 
 infection. Though it confirms Pasteur's statements in some points, it tends 
 at the same time to throw doubt on others, by making it highly probable 
 that Pasteur did not work with pure material, free from other Bacteria. It 
 makes no mention of the state of stupor. When the animals, especially 
 fowls, succumbed to the disease, death usually occurred in twenty-four 
 hours and suddenly. It is possible that Pasteur examined one infectious 
 disease and Kitt another; after the latter's thoroughly trustworthy repre- 
 sentations, Pasteur's statements certainly require critical examination. If 
 on the whole I have left them for the present in the text, I have done it 
 with this reservation, and especially on account of their importance for the 
 development of the doctrine of contagia viva, which importance they retain 
 even if they prove not to be entirely correct. 
 
 58. The following works may be consulted in special connection with 
 this section, but the reader is at the same time referred to the medical 
 
1 88 Lectures on Bacteria. 
 
 literature generally, and especially to Liebermeister's Introduction to In- 
 fectious Diseases in Ziemssen's Handbuch, II. J. Henle, Patholog. Unters. 
 I, Berlin, 1840. The works cited in note 56. de Bary, Die Brandpilze, 
 Berlin, 1853 ; Id., Recherches sur le developpement de quelques cham- 
 pignons parasites in Ann. d. sc. nat. (Botanique), ser. 4, XX. Frank, Die 
 Krankh. d. Pflanzen, Breslau, 1880. de Bary, Morphol. and Biol. of the 
 Fungi, &c., Clarendon Press, 1887; Id., in Jahresber. ii. d. Leistungen u. 
 Fortschr. d. Medicin, herausg. von Virchow u. Hirsch, II (1867), Abth. I, 
 p. 240; Id., Ueber einige Sclerotienkrankheiten, &c., in Bot. Ztg., 1886. 
 v. Recklinghausen, in Berichte d. Wiirz burger phys.-med. Ges., 1871. 
 
 E. Klebs in numerous papers, especially in Archiv f. experiment. Pathol. u. 
 Pharmacol. I (1873). v. Nageli, Die niederen Pilze, Miinchen, 1877. 
 
 59. O. Obermeier, in Berliner klin. Wochenschr. 1873. Cohn, Beitr. 
 z. Biol. d. Pfl. I, Heft 3, p. 196. v. Heydenreich, Unters. ii. d. Paras, d. 
 Ruckfalltyphus, Berlin, 1877. R. Koch in Mittheil. d. Reichsgesundheit- 
 samts, I. 
 
 60. R.Koch, Die Aetiologie d. Tuberculose, in Mittheil. d. Reichsgesund- 
 heitsamts, II. Malassez et Vignal, Tuberculose zoologique in Compt. rend. 
 XCVII (1883), P- 1006; XCIX (i88 4 \ p. 203. 
 
 61. Neisser in Centralblatt f. d. med. Wissensch., 1879, and in Deutsche 
 Med. Wochenschr., 1882, No. 20. Bockhardt, Beitr. z. Aetiologie u. 
 Pathologic d. Harnrohrentrippers, in Sitzungsber. d. phys.-med. Ges. z. 
 Wiirzburg, 1883, p. 13. E. Bumm, Der Mikroorganismus d. Gonorrhoischen 
 Schleimhaut-Erkrankungen, Wiesbaden, 1885. See also Nagel in Jahres- 
 bericht, &c. d. Ophthalmologie. 
 
 62. From the very copious literature of wound-infection, I cite here only 
 
 F. J. Rosenbach, Mikroorganismen bei d. Wundinfectionskrankheiten d. 
 Menschen, Wiesbaden, 1884. J. Passet, Unters. ii. d. eitrige Phlegmone d. 
 Menschen, Berlin, 1885. In these books and in Baumgarten's Jahres- 
 bericht will be found further information concerning the literature of the 
 subject. 
 
 63. v. Recklinghausen u. Lukomski in Virchow's Archiv, LX. Fehl- 
 eisen in Deutsche Zeitschr. f. Chirurgie, XVI, p. 391. Koch in Mittheil. d. 
 Reichsgesundheitsamts, I. 
 
 64. Sattler, Die Natur d. Trachoms, &c., in Ber. u. d. Versammlung 
 d. ophthalmol. Ges. z. Heidelberg, 1881, p. 18; 1882, p. 45. Michel, in 
 Sitzgsber. d. Wiirzb. phys.-med. Ges., 1886. 
 
 65. Kuschbert u. Neisser in Deutsche med. Wochenschr., 1884, No. 21. 
 Schleich, Zur Xerosis conjunctivae, in Nagel's Mitth. aus d. ophth. Klinik 
 z. Tubingen, II, p. 145. 
 
 66. C. Friedlander, Ueber d. Schizomyceten b. d. acuten fibrinosen Pneu- 
 monic, in Virchow's Archiv, LXXXVII (1882), p. 319 ; Id. in Fortschritte 
 d. Medic. I, 1883. For more recent confirmatory statements, see in Baum- 
 garten's Jahresbericht. 
 
 67. On leprosy, see Neisser in Ziemssen's Handb. d. spec. Pathol. u. 
 
Literature and Notes. 189 
 
 Therapie, XIV. For more recent works on leprosy, by Unna and others, 
 see in Baumgarten's Jahresbericht, and also for discussions on the Bacillus 
 of Syphilis. 
 
 68. Mittheil. d. Reichsgesundheitsamts, I. 
 
 69. Bellinger in Ziemssen's Handb. III. Loffler u. Schiitz in Deutsche 
 med. Wochenschrift, 1882, p. 707. O. Israel in Berliner klin. Wochenschr., 
 1883, p. 155. Kitt in Jahresber. d. k. Thierarzneischule Miinchen, Leipzig, 
 1885. 
 
 70. Bellinger u. Feser in Deutsche Zeitschr. f. Thiermedicin, 1878-1879. 
 T. Ehlers, Unters. ii. d. Rauschbrandpilz ; Dissert. Rostock, 1884. Kitt 
 in Jahresber. d. k. Thierarzneischule Miinchen, Leipzig, 1885. 
 
 71. E. Klein in Virchow's Archiv, XCV (1884), p. 468. For Loffler, 
 Lydtin, Schottelius, and Schiitz, see Baumgarten's Jahresbericht, 1884, p. 101. 
 
 72. Klebs und Tommasi Crudeli, Studien U. d. Ursache d. Wechselfiebers 
 u. ii. d. Natur d. Malaria, in Archiv f. experim. Pathol. XL Cuboni u. 
 Marchiafava in Archiv f. experim. Pathol. XIII. Ceci in Archiv f. 
 experim. Pathologic, XV and XVI. Ziehl in Deutsche med. Wochen- 
 schrift, 1882, p. 647. Marchiafava u. Celli, N. Unters. ii. d. Malaria- 
 Infection, &c., 1885. See Baumgarten's Jahresbericht, 1885, p. 153. I know 
 these authors only from this report. Laverans' book, cited in it, I do not 
 know. A criticism of the statements of the Italian observers, as they lie 
 before me, would be out of place here ; I would only counsel them to study 
 attentively the zoologico-botanical literature of that portion of natural 
 history with which their writings are occupied, before they deal with it so 
 independently, and employ terms like ' plasmodium,' for the word is 
 applied with the utmost precision to a portion of developmental history 
 which the authors have never observed in the cases which they are dis- 
 cussing. 
 
 73. Gaffky, Zur Aetiologie d. Abdominaltyphus, in Mitth. aus d. k. 
 Reichsgesundheitsamt, II, 372, where the literature is given at length. 
 
 74. Fr. Loffler, Unters. ii. d. Bedeutung d. Mikroorganismen fur d. Ent- 
 stehung d. Diphtherie beim Menschen, bei d. Taube u. beim Kalbe in Mitth. 
 aus d. k. Reichsgesundheitsamt, II, p. 421. 
 
 75. J. M. Klob, Pathol. anatom. Studien ii. d. Wesen d. Choleraprocesses, 
 Leipzig, 1867. R. Koch in Berliner klin. Wochenschrift, 1884, Nos. 31- 
 32 a; Id. in Verhandl. d. zweiten Conferenz z. Erorterung d. Cholerafragen in 
 Berlin, klin. Wochenschrift, 1885, No. 37 a. E. van Ermengem, Recherches 
 sur le Microbe du Cholera Asiatique, Paris et Bruxelles, 1885. F. Hueppe, 
 Ueber d. Dauerformen d. sogen. Kommabacillen, in Fortschritt d. Medicin, 
 III, 1885, No. 19, and in Deutsche med. Wochenschrift, 1885, No. 44. 
 For Nicati u. Rietsch, Doyen, Watson Cheyne, Babes, and others, see the 
 citations in Baumgarten's Jahresbericht, 1885. Finkler u. Prior in Tagebl. 
 d. sieben u. funfzigsten Ver. Deutsch. Naturf. u. Aerzte z. Magdebourg, 
 p. 216 ; Id., Forschungen U. Cholerabacterien im Erganzungsheft z. Central- 
 blatt f. allg. Gesundheitspflege, I. Emmerich, Vortr. im Aerztl. Ver. z. 
 
190 Lectures on Bacteria. 
 
 Miinchen reported in Berl. klin. Wochenschrift, 1885, No. 2 ; Id. in Arch, 
 fur Hygieine, III. H. Buchner in Arch, fur Hygieine, III. Emmerich u. 
 Buchner, Die Cholera in Palermo, in Miinchener med. Wochenschrift, 
 1885, No. 44. v. Sehlen, Bemerkungen u. d. Verhalten d. Neapler Bacillen 
 in d. Organen, &c., in Miinchener med. Wochenschrift, 1885, No. 52. 
 J. Ferran, Die Morphologic d. Cholera-Bacillus u. d. Schutz-Cholera- 
 Impfung, by Dr. Max Breiting, after Dr. Ferran, in Deutsch. median. 
 Zeitung, IV (1885), p. 160, and Ueber d. Morphol. d. Komma-Bacillus in 
 Zeischr. f. klin. Medicin, edited by Leyden, Bamberger, and Nothnagel, 
 IX (1885), p. 375, t. 1 1. Cholera, Inquiry by Doctors Klein and Gibbes, and 
 Transactions of a Committee convened by the Secretary of State for India 
 in Council, 1885. See also E. Klein in Proceedings of the Royal Soc. of 
 London, XXXVIII, No. 236, p. 154. T. Lewis in the Lancet, Sept. 2, 1884. 
 The account given in the text is founded on the literature quoted 
 above, and has been modelled chiefly on van Ermengem's excellent book. 
 The botanical description of the Spirillum of cholera is also founded partly 
 on the numerous descriptions and figures which we possess, partly on my 
 own examination of Finkler's and Prior's form. I was limited to this, 
 because my request for a specimen of living material of the Spirillum of 
 cholera, addressed to those most able to grant it, was refused, and my other 
 occupations precluded the possibility of my travelling in search of the 
 disease. I still call Koch's form and others like it by the name of Spirillum, 
 simply for the sake of shortness and simplicity. Hueppe proposes that it 
 should be called Spirochaete ; Schroter would use the word Microspira as 
 the generic name for the arthrosporous spiral Bacteria. My only objection 
 to this is that changes and shifting of names in this group of organisms 
 appear to me at present to be of little use and not desirable. The different 
 species are still so unequally known that fresh changes may at any moment 
 be required, and the best plan, therefore, is to be content with a simple 
 intelligible expression for each case, and await the time when our knowledge 
 will allow of our introducing a correct nomenclature, and one that may last 
 for some time. 
 
 76. See the compilation by Judeich and Nitsche, Lehrb. d. mitteleurop. 
 Forstinsectenkunde. Pasteur, Etudes sur la maladie des vers-a-soie, Paris, 
 1870, with notices of the literature. Frank R. Cheshire and W. Watson 
 Cheyne, The Pathogenic History and History under Cultivation of a new 
 Bacillus (B. alvei), the cause of a disease of the hive-bee, hitherto known 
 as foul brood, in Journ. of Roy. Microsc. Society, ser. a, V. S. A. Forbes, 
 Studies on the contagious diseases of insects, in Bull, of the Illinois State 
 Laboratory of Nat. Hist., II (1886). Also Metschnikoff in Virchow's 
 Archiv, XCVI, p. 178. 
 
 77. J. H. Wakker, Onderzoek d. Ziekten van Hyacinthen, Harlem, 1883, 
 1884. See also Bot. Centralblatt, XIV, p. 315. T. J. Burrill, Anthrax of 
 fruit trees, or the so-called fire-blight of pear trees, and twig-blight of apple 
 trees, in Proceedings of American Association for the advancement of 
 
Literature and Notes. 191 
 
 Science, XXIX, 1880 ; Id., Bacteria as a cause of disease in plants, in the 
 American Naturalist, July, 1881. J. C. Arthur, Pear Blight, in Annual 
 Report of the New York Agricult. Experiment Station for 1884 and 1885 ; 
 Id. in Botanical Gazette, 1885 > Id. in American Naturalist, 1885. 
 E. Prillieux, Corrosion de grains de ble, &c. , par les Bacteries, in Bull. Soc. 
 Bot. de France, XXVI (1879), PP- 3 T > 167. Reinke u. Berthold, Die Zer- 
 setzung d. Kartoffel durch Pilze, Berlin, 1879. van Tieghem, Developpe- 
 ment de 1'Amylobacter dans les plantes a 1'etat de vie normal, in Bull. 
 Soc. Bot. de France, XXXI (1884), p. 283. 
 
INDEX. 
 
 Achorion, 146. 
 Arthrobacterium aceti, 86. 
 
 Bacillus, 73. 
 
 alvei, 174. 
 
 Amylobacter, 5, 12, 17, 19, 21, 
 34, 39, 5, 53, 54, 5, 69, 70, 
 71, 99, &c., 104, 116, 179. 
 
 Anthracis, 12, 17, 21, 34, 50, 51, 
 5 2 54, 59, 64, n6, 122, &c. 
 
 butylicus, 53, 100. 
 
 butyricus, 100. 
 
 crassus, 3. 
 
 erythrosporus, 19. 
 
 lacticus, 94. 
 
 Malariae, 170. 
 
 Megaterium, 16, 17, 21, 29, 39, 
 51, 59, 104 154. 
 
 Melittopntnorus, 174. 
 
 of butyl-alcohol, 57, 70. 
 
 of butyric acid, 100. 
 
 of lactic acid, 94, 97. 
 
 of leprosy, 170. 
 
 of syphilis, 170. 
 
 of tubercle, 51, 152, 158. 
 
 of typhoid fever, 171. 
 
 of typhus, 151. 
 
 subtilis, 12, 17, 20, 29, 34, 39, 
 
 5, 5 1 , 5 2 , 54, 57, 59, I02 > I0 4, 
 124, 134. 
 
 Ulna, 17. 
 
 Ureae, 84. 
 
 virens, 4. 
 Bacterium aceti, 86. 
 
 chlorinum, 55. 
 
 merismopoedioides, u. 
 
 of lactic acid, 97. 
 
 photometricum, 58. 
 
 - Termo, 50, 53, 105, &c., 119. 
 
 Zopfii, 18, 22, 53, 116. 
 Beech, 112. 
 
 Beggiatoa, 3, 5, 23, 30,66, 73, 79,81. 
 
 alba, 81. 
 
 arachnoidea, 80. 
 
 Beggiatoa mirabilis, 80. 
 
 roseo-persicina, 5, 58, 80. 
 Botrydium granulatum, 26, 30. 
 Butyl -alcohol, Bacillus of, 57, 70. 
 Butyric acid, Bacillus of, 100. 
 
 Calothrix, 77. 
 Capitate Bacteria, 100. 
 Cholera, Spirillum of, 160. 
 Cladothrix, 7, 10, 23, 73, 76, 77, 
 
 78, 79- 
 
 dichotoma, 76. 
 Clathrocystis roseo-persicina, 80. 
 Clostridium butyricum, 100. 
 Coccobacteria septica, 28. 
 Comma-bacillus, 163. 
 
 of mucous membrane of mouth, 
 120. 
 
 Cordyceps, 109, in. 
 Cornalian bodies, 175, 176. 
 Crenothrix, 3, 7, 23, 30, 75, 76, 
 
 79- 
 
 Kiihniana, 75. 
 Cystopus, 113, 114. 
 
 candidus, 113. 
 
 Diplococci, 9. 
 Dispora, 99. 
 
 caucasica, 96. 
 Drum-stick-bacillus, 105, 116. 
 
 Erysipelas, Micrococcus of, 64. 
 Erythema migrans, 169. 
 Eurotium, 39. 
 
 Favus, 146. 
 Filamentous yeast, 67. 
 Finger-erysipelas, 169. 
 Fission-algae, 37. 
 fungi, 2, 37. 
 
 -plants, 37. 
 
 -yeast, 67. 
 Frog-spawn, 12. 
 
 bacterium, 12, 90. 
 
Index. 
 
 Galeobdolon luteum, 48. 
 Garden-cress, 63, 113. 
 Gonococcus, 156, &c. 
 
 Hay-bacillus, 12, 134. 
 Hydrocharis, 48. 
 Hydrodictyon, 26, 30. 
 
 Itch, 115, 146. 
 
 Kefir, 13, 95, &c. 
 
 Kefir, Bacterium of, 55, 95, 99, 
 
 !54- 
 Kefir-grains, 13, 95. 
 
 Labiatae, 48. 
 
 Laboulbenia Muscae, 39, in. 
 
 Lacerta viridis, 123. 
 
 Lactic acid, Bacillus of, 94, 97. 
 
 Bacterium of, 97. 
 Lepidium sativum, 63, 113. 
 Leprosy, Bacillus of, 170. 
 Leptothrix, n. 
 
 buccalis, 5, 119. 
 
 ochracea, 78. 
 
 Leuconostoc, 6, 13, 22, 23, 73, 90, 
 91. 
 
 mesentenoides, 23, 90, 91. 
 
 Merismopoedia hyalina, 185. 
 
 littoralis, 185. 
 
 punctata, 185. 
 
 Reitenbachii, 185. 
 Micrococcus aceti, 54, 86, 87, 88. 
 
 amylovorus, 178. 
 
 Bombycis, 175. 
 
 Gonococcus, 156. 
 lacticus, 33, 94. 
 
 nitrificans, 86. 
 
 of diphtheria, 172. 
 
 of erysipelas, 64. 
 
 of fowl-cholera, 141. 
 
 of tooth-caries, 121. 
 
 of ulcer, 64. 
 
 Pasteurianus, 5, 88. 
 
 prodigiosus, 14, 39, 53, 94. 
 
 Ureae, 24, 39, 84, 168, 175. 
 Microspira, 189. 
 Microzymes, 47. 
 
 Monads, 9. 
 
 Monas prodigiosa, 14. 
 Mother of vinegar, 6, 84, 86. 
 Mucor, 26. 
 
 Mucorini, 58, 70, 71. 
 Mycoderma aceti, 86. 
 Mycothrix, n. 
 Myxomycetas, 112. 
 
 Naples Bacillus, 165. 
 Nosema Bombycis, 175. 
 Nostoc, 36. 
 Nostocaceae, 6, 36, 77. 
 
 Oenothereae, 112. 
 Ophiodomonas, 79. 
 Oscillatorieae, 8, 36, 80, 82. 
 
 Palmella, 12. 
 
 Panhistophyton ovatum, 175. 
 Penicillium glaucum, 39, 56. 
 Phytophthora infestans, 112, 179. 
 
 omnivora, 112. 
 Proteus, 183. 
 Pythium, 112. 
 
 Relapsing fever, 151. 
 Rusts, 1 08. 
 
 Saccharomyces, 70, 71, 90, 98. 
 
 Cerevisiae, 68, 69, 98. 
 
 Mycoderma, 89. 
 
 of beer-yeast, 70, 90, 98. 
 Salvia glutinosa, 48. 
 Saprolegnieae, 38. 
 Sarcina, 73, 117. 
 
 flava, 1 1 8, 184. 
 
 fuscescens, 185. 
 
 hyalina, 185. 
 
 intestinalis, 185. 
 
 littoralis, 185. 
 
 lutea, 1 1 8, 184, 185. 
 
 minuta, 117, 184. 
 
 of the lungs, 185. 
 
 paludosa, 185. 
 
 Reichenbachii, 185. 
 
 Reitenbachii, 1,854 
 
 rosea, 185. 
 
 ventriculi, 5, n, 116, 117, 118, 
 184. 
 
 - Welcheri, 118, 184. 
 Schizomycetes, 2. 
 Schizophytes, 37. 
 Sclerotinia, 112. 
 Scytonema, 77. 
 Sempervivum, 112. 
 
Index. 
 
 193 
 
 Spirillum, 10, 27, 50, 60, 73, 120, 
 
 151, 160. 
 -'amyliferum, 5, 17. 
 
 of cholera, 160. 
 
 tenue, 82. 
 - Undula, 82. 
 
 Spirochaete, 6, 27, 189. 
 
 buccalis, 120. 
 
 Cohnii, 119, 120, 151. 
 
 dentium, 1 20. 
 
 Obermeieri, 151, 158. 
 Sprouting yeast, 67. 
 Staphylococcus, 168. 
 
 albus, 168, 169. 
 
 aureus, 168, 169. 
 Streptococcus, 24, 168, 169. 
 Syphilis, Bacillus of, 170. 
 
 Tapeworms, 108, 115. 
 Trianea bogotensis, 48. 
 
 Trichina spiralis, in. 
 Trichinae, 108, 115, 146. 
 Tubercle, Bacillus of, 51, 152, 159. 
 Typhoid fever, Bacillus of, 171. 
 Typhus, Bacillus of, 151. 
 Tyrothrix, 52, 104. 
 
 filiformis, 52. 
 
 tenuis, 52, 104. 
 
 Ulcer, Micrococcus of, 64. 
 
 Ulothricheae, 82. 
 
 Urea, Micrococcus of, 24, 39, 84, 
 
 168, 175. 
 Uredineae, 108. 
 
 Vibriones, 10, 159. 
 
 Vinegar, Bacterium of, 70, 94. 
 
 Micrococcus of, 57, 86, &c. 
 
 Zoogloea, 12. 
 
 THE END. 
 
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