LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 GIKT OK 1 
 
 Mrs. SARAH P. WALSWORTH. 
 
 Received October, 
 Accessions No. 5^1 tr /Q Class No. 
 
c 
 
ACTONIAN PRIZE ESSAY. 
 
CHEMISTRY, 
 
 AS EXEMPLIFYING 
 
 THE WISDOM AND BENEFICENCE OF GOD, 
 
 GEORGE FOWNES, PH.D. 
 II 
 
 CHEMICAL LECTURER IN THE MIDDLESEX-HOSPITAL MEDICAL SCHOOL. 
 
 % J*- 
 
 NEW-YOEK : 
 WILEY AND PUTNAM 
 
 PHILADELPHIA: 
 
 J. W. MOORE. 
 
 1844. 
 
&D39 
 
TO THE 
 
 PRESIDENT, MANAGERS, AND MEMBERS 
 
 OF THE 
 
 ROYAL INSTITUTION OF GREAT BRITAIN, 
 
 IS MOST RESPECTFULLY DEDICATED. 
 

PREFACE. 
 
 IN the year 1838, Mrs. Hannah Acton, widow of 
 the late Samuel Acton, Esq., of Euston Square, from 
 motives of respect and regard for the memory of her 
 deceased husband, and in order to carry into effect 
 his desire and intention, caused an investment to be 
 made of the sum of One Thousand Pounds in the 
 three per cent. Consol. Bank Annuities, in the names 
 of the trustees of the Royal Institution of Great Brit- 
 ain, the interest of which was to be devoted to the 
 formation of a fund, out of which the sum of One 
 Hundred Guineas was to be paid septennially, as are- 
 ward or prize to the person, who, in the judgment of 
 the committee of managers for the time being of the 
 Institution, should have been the author of the best 
 essay illustrative of the wisdom and beneficence of 
 the Almighty, in such department of science as the 
 committee of managers should, in their discretion, 
 have selected the form and conditions of the essay 
 being also, in a great measure, left to the choice of 
 that body. 
 
 The subject chosen for the prize of the first period 
 of seven years, was " Chemistry, as exemplifying the 
 wisdom and beneficence of God." The prize was 
 
8 PREFACE. 
 
 awarded in April last ; and having, on this occasion, 
 had the happiness to be the fortunate "candidate, I 
 now beg to offer to the notice of those who feel inter- 
 ested in such matters the essay in question, satisfied 
 that my labour will not have been in vain if the 
 smallest support drawn from the magnificent science 
 of chemistry shall be found to have been given to the 
 Great Argument. 
 
 I have to express my great obligations to the 
 Committee of Managers for their kindness in grant- 
 ing me permission to print the work, which has been 
 done without alteration from the original manuscript, 
 the property of the Institution. 
 
 GEO. FOWNES. 
 
 MIDDLESEX HOSPITAL, 
 May 14, 1844. 
 
INTRODUCTION 
 
 THE study of the structure of the animal frame not 
 only gives proof of the most exquisite mechanical 
 beauty of contrivance in each case, but of the exist- 
 ence of a general plan or type of organization, 
 modified to suit the circumstances of the creature, 
 but always to be traced ; further, this general type 
 extends to the animals of the ancient world, whose 
 remains have been preserved in the solk! rock. 
 
 Comparative anatomy and physiology have con- 
 tributed, perhaps, more than any other subjects to 
 the argument of foresight, design, and contrivance, 
 in the works of creation. The parallel between the 
 watch and the eye has been extended to many more 
 cases than those originally contemplated. Every 
 microscopical investigation brings to light new in- 
 stances, each more wonderful than its predecessor. 
 The exact adaptation of the habits, instincts, and 
 appetites of the creature to the circumstances under 
 which it is destined to live; the way in which the 
 individual happiness of the animal, and the perma- 
 nence of the race, have, by a most elaborate series 
 
10 INTRODUCTION. 
 
 of checks and counterpoises, been secured ; all have 
 been adduced with the greatest success, as so many 
 proofs of wisdom, design, and benevolence on the 
 part of the great Contriver. These adaptations, it 
 must be remembered, are not merely visible in a 
 few scattered cases; they are universal : they extend 
 to every living creature under heaven. 
 
 The higher powers and affections of man have, 
 also, been enlisted in the same great argument. 
 The necessary connexion between virtue and happi- 
 ness, vice and misery a connexion arising from the 
 very character and configuration of the mind has 
 been pointed out. The superior permanence and 
 duration of the pleasure arising from the gratifica- 
 tion of virtuous and innocent affections above that 
 caused by the exercise of malignant ones, have, 
 likewise, with justice, been insisted upon as proofs 
 of the most satisfactory kind of the benevolence, as 
 well as of the wisdom and power, of the Deity. 
 
 Lastly, the physical structure of the earth itself, 
 and the peculiar properties and constitution of the 
 atmosphere, have been minutely described, with 
 reference to the same subject. 
 
 The recent discoveries of chemistry, more espe- 
 cially in its relations to animal and vegetable phy- 
 siology, lead to the hope that it may be possible to 
 draw an inference of design from the chemical con- 
 stitution of the earth and its inhabitants, hardly infe- 
 rior in value to that derived from their physical 
 study, although not always so obvious and striking. 
 The following pages contain an attempt of the 
 kind. 
 
INTRODUCTION. 1 1 
 
 The subject will be discussed in the following 
 order : 
 
 THE CHEMICAL HISTORY OF THE EARTH, AND THE 
 
 ATMOSPHERE. 
 THE PECULIARITIES WHICH CHARACTERIZE ORGANIC 
 
 SUBSTANCES GENERALLY. 
 
 THE COMPOSITION AND SUSTENANCE OF PLANTS. 
 THE RELATIONS EXISTING BETWEEN PLANTS AND 
 
 ANIMALS. 
 APPENDIX. 
 
ON THE 
 
 CHEMICAL NATURE OF THE EARTH AND 
 ITS ATMOSPHERE. 
 
 THE researches of modern chemistry have 
 brought to light some fifty-five distinct forms or 
 modifications of matter, each of which must, in re- 
 lation to the present state of our knowledge, be 
 considered a " simple" or " elementary" substance; 
 the term " undecompounded substance" would, per- 
 haps, be more appropriate and better fitted to con- 
 vey the idea intended by the chemist. Of these nu- 
 merous bodies, more than half present that assem- 
 blage of characters to which we give the term 
 " metallic ;" such as good conducting powers for 
 heat and electricity, brilliant lustre connected with 
 the utmost opacity, and chemical energies directed 
 towards such bodies as oxygen, chlorine, iodine, sul- 
 phur, &c. These latter stand at the head of the 
 other division, the non-metallic elements of chemi- 
 cal writers, among which are to be found substances 
 of the very highest degree of importance in the 
 great scheme of Nature, from the universality of 
 their occurrence, and their intimate connexion with 
 
14 ON THE CHEMICAL NATURE OF 
 
 all the phenomena of organic life. It must not be 
 imagined, however, that this division of the known 
 elements into metals and non-metallic substances, is 
 strictly warranted ;. it is, in fact, mOre convenient in 
 practice than correct in principle, as a regular gra- 
 dation from the one class to the other can be easily 
 traced. Antimony, arsenic, phosphorus, selenium, 
 sulphur, constitute such a connecting chain between 
 the two series. 
 
 The slightest glance at the general chemical his- 
 tory of our globe will suffice to show the vast in- 
 equality in the distribution of these materials. Of 
 the interior of the earth nothing is known ; but so 
 far as the surface is concerned the only part of 
 which man can take cognizance some eight or ten 
 elements will form the whole list of substances con- 
 cerned in the formation of the great bulk and mass 
 of all those objects we see around us. The atmos- 
 phere is made up of two namely, oxygen and 
 nitrogen, with, comparatively speaking, mere traces 
 of two others, carbon and hydrogen. Two of these 
 again, oxygen and hydrogen, by their chemical 
 union, give rise to water, occupying in the shape of 
 ocean of unknown depth, lakes and rivers, nearly 
 three-fourths of the surface of our planet: the solid 
 earth we dwell upon is chiefly made up of the 
 oxides of one non-metallic body, silicon, and two 
 metals, aluminium and calcium, the metallic base of 
 lime. Let us add to these, potassium, whose oxide 
 is a constituent of felspar, the characteristic ingredi- 
 ent of granite ; sodium, whose great depository is 
 the water of the ocean ; and, lastly, iron, whose 
 
THE EARTH AND ITS ATMOSPHERE. 15 
 
 oxide is to be found every where to a greater or less 
 extent, and we really include all the known com- 
 ponents of our earth, which enter in large quantities 
 into its structure. 
 
 Other substances, such as sulphur in the state of 
 gypsum, (sulphate of lime,) and in union with certain 
 metals ; magnesium in its oxidized state, and a few 
 more, are found here and there, in local deposits of 
 considerable extent, while the remainder are still 
 more limited in their distribution; and, lastly, a not 
 inconsiderable number of the bodies, recognized as 
 elements, are only to be found in a few minerals so 
 exceedingly rare, that scarcely a sufficient supply of 
 the material can be had for the use of the experimen- 
 tal chemist. 
 
 In the organic world the same, or still greater, 
 simplicity is observed ; carbon, hydrogen, oxygen, 
 and nitrogen, a little phosphorus and sulphur, and 
 sometimes a small proportion of two or three alkaline 
 and earthy salts, are the sole materials which have 
 been employed in the construction of those countless 
 multitudes of orders of living objects which people 
 the earth, and clothe it with beauty. 
 
 But, then, this apparent paucity of original mate- 
 rials is more than compensated by the very peculiar 
 properties of some of those selected. The four first 
 mentioned namely, carbon, hydrogen, oxygen, and 
 nitrogen are distinguished above all other bodies 
 by the innumerable compounds they are capable of 
 forming, by union among themselves. Modern or- 
 ganic chemistry, vast as it already is, consists of little 
 
16 ON THE CHEMICAL NATURE OF 
 
 more than the study of these four elements and their 
 combinations. 
 
 It forms no part of the object of the present trea- 
 tise to point out to the reader the advantages which 
 mankind derive from the particular mode of structure, 
 or arrangement, of the beds and masses of rock 
 which form the solid earth, made known to us by 
 geology; this has already been done by very able 
 hands. The evident design and contrivance exhibit- 
 ed in the disposition of our mineral treasures is well 
 fitted to excite in the mind the conviction of fore- 
 thought and provision for man's necessities and com- 
 fort. What can be more striking, for example, than 
 the aspect of an English coal-field, where iron-ore of 
 excellent kind lies interstratified with the fuel neces- 
 sary to reduce it ; where the limestone, used as a 
 flux, and even the very grit and fire-clay to build 
 the furnace, are all to be found in one and the same 
 series, often within a few yards of each other. If 
 the ore and the fuel were not thus so curiously relat- 
 ed, we should be deprived, by the vastly increased 
 price of the manufactured article, of the power we 
 now enjoy of applying this noblest of all the metals 
 to innumerable purposes of daily life and conveni- 
 ence. 
 
 It is not in one particular case alone that this 
 association of iron ore and fuel is observable. The 
 mountains of Sweden and Norway contain inex- 
 haustible beds of magnetic iron-ore; a variety so 
 rich in quality, and so free from deleterious admix- 
 ture of foreign matter, as to yield, when reduced by 
 
THE EARTH AND ITS ATMOSPHERE. 17 
 
 charcoal, the finest and purest bar-iron for making 
 steel, and other purposes where great purity in the 
 metal is desirable. Now the only fuel at all fit for 
 employment in the manufacture of this excellent iron 
 is wood-charcoal, and, accordingly, forests of pines 
 have, by the provident hand of Nature, been planted 
 in these otherwise barren and desolate regions, by 
 the aid of which the iron-maker pursues his labours, 
 thus rendered profitable to the whole community. 
 
 This is but a single case out of the many which 
 geology can bring forward as exhibiting prospective 
 contrivance, beneficially exerted, in the structure 
 of the earth ; a more minute, and more chemical 
 examination of the subject may, perhaps, even now, 
 in the very imperfect state of our knowledge on 
 many points, tend to strengthen this opinion. 
 
 The great mountain-chains which ridge and fur- 
 row the earth's surface, and upon whose flanks and 
 lower slopes rest the different stratified aqueous de- 
 posites of conglomerate, and slate, and sandstone, 
 and calcareous matter, in all their endless modifica- 
 tions, great part of which have been directly derived 
 from the mechanical degradation of the central 
 mountain-nucleous itself, by the agency of moving 
 water, consist of one and the same material in all 
 parts of the known earth namely, granite. It is 
 not at random, that this one particular substance has 
 been taken, as a material out of which to construct 
 the great framework or skeleton of our habitation ; 
 that, on the contrary, it has been, as it were, delib- 
 erately chosen out of many others, so far as their 
 physical properties are concerned, equally good ma- 
 
18 ON THE CHEMICAL NATURE OF 
 
 terials, from a previous precise knowledge of its pe- 
 culiar chemical fitness for the office in question ; 
 and this it is not very difficult to show, so far as such 
 a thing can be shown. 
 
 One of the most obviously indispensable con- 
 ditions of all animal existence is a supply of food ; 
 this supply must, it is equally clear, be derived, either 
 directly from the vegetable kingdom, or indirectly, 
 in the case of the carnivorous races, whose nutriment 
 is drawn from the flesh of plant-eating animals : 
 animal life, therefore, necessarily presupposes vege- 
 tation, and is. regulated in its extent by the luxuri- 
 ance or deficiency of the latter. Now all plants, as 
 will hereafter be noticed, derive, in the first instance, 
 the whole of their " organic constituents" (by which 
 term the elements carbon, hydrogen, oxygen, and 
 nitrogen, are signified) from the atmosphere which 
 bathes their foliage, and from the rain-water which 
 is absorbed by their roots. Plants, however, con- 
 tain in every case, without a single exception, other 
 substances besides the four mentioned, although in 
 very much smaller proportion, but which cannot 
 be looked upon as accidental, since experience has 
 shown them to be quite indispensable to vegetable 
 life; moreover, the constancy of their occurrence, 
 and their different nature in different plants, and 
 even in different parts of the same plant, all point 
 to this conclusion. Such bodies are the alkalis, 
 potash, and soda, phosphoric and sulphuric acids, 
 lime and magnesia, silica, and, perhaps, a few oth- 
 ers; these form the contingent of food really fur- 
 nished by the soil in which the plant grows, and are 
 
THE EARTH AND ITS ATMOSPHERE. 19 
 
 each in its turn as necessary to its well-being as the 
 carbonic acid, or the water it gets from the air. 
 
 Of these inorganic principles, one of the most 
 indispensable of all to land-vegetation, with which 
 we are principally concerned, is potash ; there is not 
 a single vegetable in the field or the wood, the ashes 
 of which does not contain this substance in one state 
 of combination or another, and often in very large 
 quantity, so much so, that an idea was once held 
 that plants possessed the power of generating the 
 substance within themselves; an opinion which 
 more careful inquiry has ifegatived, by showing the 
 real source of the alkali, and the state in which it 
 exists in the soil. 
 
 Another, perhaps equally important substance, 
 is phosphoric acid, a body as universally diffused 
 in the vegetable kingdom as potash itself; not a 
 plant can be found from which phosphates are ab- 
 sent. Indeed it is easy to see the reason of this pro- 
 vision, if the important function fulfilled by one of 
 the earthy phosphates in the animal economy be 
 considered for a moment : it is phosphate of lime 
 which gives strength and stiffness to the bony frame- 
 work of the animal body, and which salt must be 
 furnished by the food the creature subsists upon. 
 Taking into account, therefore, the fact that there is 
 scarcely a green plant which does not furnish sup- 
 port to one or other of the vegetable feeders among 
 the higher orders of the animal kingdom, it is easy 
 to see the reason why of set purpose such a relation 
 should have been established between the ultimate 
 function and office of the plant namely, the main- 
 
20 ON THE CHEMICAL NATURE OF 
 
 tenance of sentient life, and a condition indispensa- 
 ble to the growth of the plant itself. Suffice it to 
 say, as the result of exact experimental investiga- 
 tion, that without potash and phosphoric acid vege- 
 table life cannot go on, much less flourish. 
 
 Now let us inquire for a moment what sources 
 of these two substances we possess in the solid earth 
 itself; both are now, in the advanced state of analy- 
 sis, easily discovered when sought for by appropriate 
 means. We find, on making the investigation, that 
 hardly a rocky bed can be examined without both 
 coming to light often mere traces, it is true, but 
 still they are present. Here, however, a difficulty 
 occurs, at least with one of them ; with the excep- 
 tion of a very small group of the oldest sedimentary 
 rocks, every stratum, almost without exception, from 
 the tertiary formations to the ancient slate, contains 
 embedded the remains of formerly existing races 
 *of animals. The shells and bones of those crea- 
 tures contain phosphate of lime, which thus becomes 
 a constituent part of the rock itself; and from the 
 comminuted state in which these remains are often 
 found, it may easily happen, that the salt may be 
 discovered in portions of the bed where no organic 
 remains are perceptible to the eye, and yet be really 
 derived from this source alone. 
 
 Dr. Schweitzer, of Brighton, in an analysis of the 
 chalk rock of that neighbourhood, made some little 
 time ago, discovered a notable quantity of phosphate 
 of lime, and attributed it, with great show of justice, 
 
THE EARTH AND ITS ATMOSPHERE. 21 
 
 to an admixture of the shells of crustaceous animals 
 in a finely divided state, which have thus become 
 part and parcel of the present chalk bed. 
 
 Whence, however, it may be asked, did these 
 animals get this acid component of the shelly 
 coverings ; whence the phosphate of the ichthy- 
 osaurus rock and the coprolites of the Dorsetshire 
 lias, unless phosphoric acid formed a specific in- 
 gredient of the ancient unorganized earth, provided 
 ages before the first indication of organic life at 
 all 1 Phosphorus is an elementary substance ; there 
 is not a tittle of evidence in favour of its generation 
 by living beings of any kind ; it becomes, therefore, 
 highly desirable to be able to point out its original 
 place among the components of the primordial 
 earth. 
 
 Now there is every reason to think that this place 
 is to be found in the ancient massive granite, before 
 spoken of as forming the basis and foundation of 
 our present system of continents. It is true that 
 phosphoric acid has not been directly found, to my 
 knowledge, in this situation, in either the felspar or 
 the mica of this rock ; but then phosphoric acid in 
 union with alumina, as it may be expected to be in 
 these cases, is a substance particularly easy to over- 
 look in analytical inquiries, as almost every chemist 
 knows to his annoyance, and it is not at all unlikely 
 that proper and diligent search would be rewarded 
 with success. 
 
 There are many circumstances which tend to 
 point out phosphoric acid as an original constituent 
 of one or more 'granite minerals. Crystallized phos- 
 
22 ON THE CHEMICAL NATURE OF 
 
 phate of lime is not unfrequently found lining the 
 sides of small cavities in this rock ; a massive varie- 
 ty occurs in some abundance in more than one pri- 
 mary district; phosphate of lead is found in some of 
 the Cornish mines ; phosphate of alumina, in a 
 crystallized condition, is met with in an ancient 
 slate deposit ; and many other cases might be cited 
 in evidence of the presence of phosphorus in the old 
 crystalline igneous rock.* 
 
 The theory of the origin of potash from the 
 same source is in the highest degree satisfactory. It 
 is well known that felspar forms four-fifths, at least, 
 of all ordinary granite ; and further, that this miner- 
 al contains beween fourteen and fifteen per cent, of 
 potash. It is, in fact, a true saline combination, a 
 double silicate of alumina and that alkaline base, 
 corresponding to common alum, only having silicic 
 acid in place of sulphuric. It is also generally 
 remarked that this felspar is subject to decomposi- 
 tion by the agency of the weather, and chemical 
 examination has made pretty clear the general na- 
 ture of the change. It is, in fact, a case in which 
 an insoluble saline substance is slowly decomposed 
 by contact with water a circumstance by no means 
 
 * Since the above was written, the author has succeeded 
 in finding phosphoric acid in considerable quantity in the 
 porcelain clay of Cornwall, and in the decomposed granite 
 by which it is furnished. The same substance was also 
 found in several specimens of lava from different localities. 
 The felspar of sound unaltered granite yielded but indistinct 
 indications of phosphoric acid, which may probably be as- 
 cribed to the greater difficulty of the investigation. See Ap- 
 pendix, No. I. 
 
THE EARTH AND ITS ATMOSPHERE. 23 
 
 uncommon ; potash, retaining some silica, is dis- 
 solved out; silicate of alumina, with the residue of 
 the silicate of potash, remains behind ; this still 
 slowly undergoes decomposition in the same way, un- 
 til at length little else remains but silicate of alumina, 
 or "clay," the form and appearance of the original 
 felspar being utterly lost. This ultimate change, 
 however, is a very slow one indeed j ages and ages 
 elapse before all the alkali is extracted from the 
 aluminous portion, from the compact and insoluble 
 state in which it existed in the felspar. 
 
 These remarks will suffice to render, to a certain 
 extent, intelligible the fact of the constant presence 
 of potash in every fertile soil that has been examined, 
 that is, every soil containing a due proportion of 
 clay, the product, either immediate or remote, of the 
 decomposition of a felspathic rock. This potash in 
 the soil is in an insoluble form, not to be extracted 
 by mere treatment with water ; it is only to be dis- 
 covered by a regular analysis, in which the finer part 
 of the soil, deprived of its organic matter, is decom- 
 posed at a white heat by carbonate of baryta, or 
 lime, or when it is acted upon for some hours with 
 boiling oil of vitriol. In this insoluble state, it resists 
 the solvent power of the rain water, which would 
 otherwise carry it away and reduce the land to bar- 
 renness in a few years, and is only set free, little by 
 little, by the long-continued contact of that liquid, 
 aided by the alternations of frost and heat, in just 
 sufficient quantity for the use of plants growing in 
 the soil, whose rootlets then absorb it with facility. 
 
 It is not, then, by blind chance that granite occu- 
 
24 ON THE CHEMICAL NATURE OF 
 
 pies so important a place in the framework of our 
 earth ; indeed it may be said of rocks of igneous ori- 
 gin generally, both ancient and modern, that they 
 are the natural depositories of the alkalies, which, 
 by their slow disintegration, become liberated, and 
 contribute to spread fertility and abundance over 
 the face of the globe, and perhaps to perform other 
 functions of not less importance, when they at length 
 reach their last resting-place, the great ocean. 
 
 The whole subject of the formation of cultivable 
 soils, and their distribution over the earth's surface, 
 is replete with interest and instruction. Every earth- 
 quake which has, in by-gone times, fractured and 
 dislocated the solid strata, every flood which has 
 swept over the ancient continents, every change of 
 level which has elevated the bed of the ocean or 
 depressed the land beneath its surface, has contrib- 
 uted, more or less, to bring about that mixture of 
 materials sand, clay, and calcareous matters 
 which now form the earth's upper Covering the 
 fruit-bearing soil, the inexhaustible source of pros- 
 perity and strength. Surely, it is not too much to 
 infer that all these things had reference to that future 
 condition of the earth, when it should become the 
 habitation of beings capable of appreciating the 
 wonders around them, and deriving mental support 
 and guidance from the contemplation of these won- 
 derful p ovisions, while enjoying with thankfulness 
 the physical comforts to which they give rise. 
 
 The saltness of the ocean has usually been regard- 
 ed as a special provision of nature to guard against 
 certain inconveniences which might otherwise have 
 
THE EARTH AND ITS ATMOSPHERE. 25 
 
 resulted. The presence of so much saline matter in 
 solution depresses the freezing point of the water 
 many degrees, thereby diminishing the dangerous 
 facility with which fields of ice are produced in the 
 polar regions. It has been said, also, that the salt 
 is useful in checking evaporation, and also that it 
 aids in preventing the corruption of the water by 
 the accumulation of animal and vegetable remains. 
 Without for a moment questioning the incidental 
 benefits resulting from the circumstances under dis- 
 cussion, and which, in one case at least, are quite 
 obvious, it may be suggested that the saltness of the 
 sea may be considered rather an inevitable result of 
 the present disposition of things, than a special ar- 
 rangement expressly intended to fulfil certain par- 
 ticular objects. 
 
 The rain which falls upon the earth is due to the 
 condensation of aqueous vapour previously existing in 
 the atmosphere, and which is supplied in great part 
 by evaporation from the surface of the sea the area 
 of the latter compared with that of the land being 
 very great, necessarily so perhaps, to furnish the 
 requisite extent of evaporating surface. This 'water 
 is, as is well known, perfectly fresh and pure, the 
 saline constituents of the ocean having no sensible 
 degree of volatility at the temperature at which the 
 vapour has been raised. No sooner, however, does 
 it reach the earth than it becomes contaminated with 
 soluble substances which it meets while flowing on 
 the surface of the ground or percolating beneath. 
 It is thus that the waters of springs and rivers inva- 
 riably contain a greater or less amount of alkaline 
 * 3 
 
26 ON THE CHEMICAL NATURE OF 
 
 and earthy salts, which all eventually find the way 
 into the sea, and there remain, since there is no chan- 
 nel for their return. The saline condition of sea- 
 water is but an exaggeration of that of ordinary 
 lakes, and rivers, and springs ; the materials are the 
 same, and of necessity so ; the ocean being, in fact, 
 the great depository of all the soluble substances 
 which, during innumerable ages, have been separa- 
 ted by a process of washing from the land. The 
 case of the sea is but a magnified representation of 
 what occurs in every lake into which rivers flow, 
 but from which there is no outlet except by evapo- 
 ration. Such a lake is invariably a salt lake. It is 
 impossible that it can be otherwise ; and it is curious 
 to observe that this condition disappears when an 
 artificial outlet is provided for the waters. It will 
 be remembered that the saltness of the ocean is very 
 far exceeded by that of several inland lakes of the 
 kind described. That of Aral near the Caspian, 
 and the Dead Sea in Judea, are remarkable exam- 
 ples. 
 
 The nature of the substances thus extracted 
 from the bosom of the earth, and carried seaward, 
 deserves attention. The most abundant of all is 
 usually common salt ; next, certain combinations of 
 magnesia ; then, salts of lime, the carbonate held 
 in solution by excess of carbonic acid, the sulphate, 
 perhaps, in addition ; and, lastly, comparatively 
 small proportions of potash and oxide of iron, with 
 mere traces of bromides and iodides. The occa- 
 sional occurrence of large proportions of the last- 
 named bodies in the springs of a few districts is 
 
THE EARTH AND ITS ATMOSPHERE. 27 
 
 phenomenon dependent upon local causes, no 
 doubt the peculiar nature of the rock through which 
 the water rises. 
 
 Such are the foreign substances diffused in 
 greater or less proportion in all the waters we em- 
 ploy for the various purposes of life, and which are 
 accumulated, or concentrated, as it were, in that of 
 the sea to a far greater extent. 
 
 Some of these principles possess, however, obvi- 
 ous and palpable uses when thus dissolved. It is 
 highly probable that the iodine of sea-water is con- 
 nected in some way with the well-being of sub- 
 marine vegetation ; that it forms an indispensable 
 component of the food of these plants. It iis diffi- 
 cult to account on any supposition for its constant 
 occurrence in certain of them. They appear to 
 have the power of seeking out and appropriating 
 to themselves the almost infinitesimal quantity of 
 iodine which analysis indicates in sea-water. Again, 
 the lime-salts have their use, and a most important 
 one it is. Shell- fish and coral polyps depend upon 
 them for the material of their curious structures. 
 The geologist and the navigator will readily appre- 
 ciate the extent to which the surface of the globe 
 has been altered and modified both in ancient and 
 modern times by the silent labours of myriads of 
 these creatures, all engaged in the production of 
 calcareous matter. The limestones of this and 
 other countries are often visibly made up of the 
 relics of these animals ; and even when, from com- 
 minution, these cease to be apparent to the eye, the 
 microscope yet discovers them. It may even be 
 
28 ON THE CHEMICAL NATURE OF 
 
 that all limestones, with some trifling exceptions, are 
 of animal origin; and that when organic remains 
 are not found, the r< ason is to be sought in their 
 obliteration by partial fusion. 
 
 It is very possible, also, that what we are accus- 
 tomed to call impurities in ordinary water may be 
 of great service to the living system. These mat- 
 ters are admitted to exercise an influence upon the 
 body in particular states of disease ; and if so, it is 
 unlikely that they should be altogether inactive in 
 health. Pure distilled water, even after long expo- 
 sure to the air, is exceedingly vapid and disagreea- 
 ble to the taste, which may be taken as a sort of 
 indication of its unfitness for ordinary use. 
 
 A review of the properties of the different com- 
 pounds of the rarer elementary bodies rare in the 
 sense already adverted to will serve to show that 
 their action upon the animal system is almost invari- 
 ably prejudicial, and often highly poisonous even in 
 small quantities. Among the metals, for exarnple, 
 almost the only one, the oxide of which is harmless 
 to the living body, is the metal iron. If the oxides 
 of copper or of lead were as widely diffused as this 
 substance, the result would be most disastrous. The 
 daily absorption into the system of minute quanti- 
 ties of metallic poisons is known to be followed by 
 consequences of a fearful kind. Too many such 
 cases are unfortunately on record. Had carbonate 
 of baryta been as abundant as carbonate of lime, 
 animated life would, in all probability, have failed 
 before its deadly influence. It is difficult to avoid 
 the conclusion that Jhe arrangements described have 
 
THE EARTH AND ITS ATMOSPHERE. 29 
 
 been made with special reference to the properties 
 of the bodies employed, and that an intelligent choice 
 has really been exercised in their selection. 
 
 Let us now turn for a moment to the chemical 
 study of the atmosphere. The plan of the present 
 work renders it unnecessary to discuss the experi- 
 mental evidence of the composition of the air. 
 Suffice it to say, that in the atmosphere can be de- 
 tected at least four distinct elementary substances 
 namely, oxygen, nitrogen, hydrogen, and carbon. 
 The mode in which these are arranged is as follows : 
 the great bulk of the air is made up of a mixture of 
 oxygen and nitrogen gases in the proportion of 
 twenty-one measures of the former to seventy-nine 
 of the latter. The two gases are in a state of mere 
 mechanical mixture, not chemically combined. In 
 addition to these, are to be found a little carbonic 
 acid gas, usually about ^- O th part by measure of the 
 whole, but subject to occasional slight variation ; a 
 quantity of vapour of water, depending very much 
 upon the temperature ; and, lastly, a just distinguish- 
 able trace of carbonate of ammonia. These are 
 the only substances yet demonstrated to exist in air 
 collected in the open country at a distance from 
 towns. 
 
 Now, in casting a glance over the long series of 
 accurate experiments made by different distinguished 
 individuals on specimens of air brought from dis- 
 tricts the most remote, and collected under circum- 
 stances the most dissimilar, the point that most fixes 
 the attention is the almost absolute identity of com- 
 position found every where to prevail. Air from 
 
30 ON THE CHEMICAL NATURE OF 
 
 the summits of Mont Blanc and Chimborazo, from 
 Egypt and from London, from Paris at the level of 
 the Seine, and from a height of near 22,000 feet, 
 exhibited the same proportions of oxygen and ni- 
 trogen. The carbonic acid and vapour of water are 
 alone found to differ slightly. To what cause, then, 
 can we attribute this extraordinary uniformity of 
 mixture throughout the whole extent of the atmos- 
 phere, if its constituents are, as we know them to 
 be, merely mixed? Oxygen and nitrogen differ in 
 specific gravity. How comes it to pass they do 
 not separate like oil and water, and arrange them- 
 selves in the order of their densities the oxygen 
 below and the nitrogen above ? The answer to this 
 question involves what is called the " principle of 
 gaseous diffusion." 
 
 When two gases which have no chemical action 
 on each other as, for example, carbonic acid and 
 hydrogen are so arranged that the vessels in which 
 they are contained communicate by a tube of narrow 
 dimensions, it is observed, after a certain time, de- 
 pendent upon the length and small diameter of the 
 tube, that perfect mixture has occurred, and that 
 hydrogen and carbonic acid are to be found in the 
 same proportions in both vessels. This facility pos- 
 sessed by the two gases, of diffusion into each other, 
 is not interfered with even when it is made to take 
 place against the action of gravity by placing the 
 two connected vessels in an upright position the 
 carbonic acid below, and the hydrogen above. Car- 
 bonic acid is, bulk for bulk, more than twenty times 
 heavier than hydrogen ; and yet, after a few hours 
 
THE EARTH AND ITS ATMOSPHERE. 31 
 
 at the utmost, the two gases are found uniformly 
 mixed. 
 
 There are many curious facts, known to the ex- 
 perimental chemist, which illustrate this principle, 
 and which he accidentally meets with in the course 
 of his labours. A bladder or thin c'aouchouc bag 
 filled w ? ith hydrogen, and left for some time, is found 
 to contain nothing but atmospheric air. Diffusion 
 has taken place through its substance in both direc- 
 tions. A jar of gas standing over mercury becomes 
 gradually deteriorated from admixture of air creep- 
 ing in between the mercury and the glass, in conse- 
 quence of the want of complete cdhesion, or " wet- 
 ting," between^ the metal and the solid ; and the 
 chemist is often put to no small trouble and inconve- 
 nience in order to guard, in his researches, against 
 the effects of this ever-active principle. 
 
 A very curious and interesting- law, linking to- 
 gether the rapidity of diffusion of the several gases 
 and their density, has been discovered by Professor 
 Graham, and its study will be found highly interest- 
 ing to all engaged in the pursuit of natural science; 
 it will be unnecessary to discuss it in the present in- 
 stance, as the mere knowledge of the general facts 
 above described will suffice to enable the reader to 
 form some idea of the unspeakably important part 
 played by this property or quality, inherent in the 
 constitution of all gaseous substances, in the great 
 economy of nature. There are processes constantly 
 going on around us in which gaseous matter and 
 vapours, prejudicial in the highest degree to animal 
 life, are unceasingly evolved ; the function of respi- 
 
32 ON THE CHEMICAL NATURE OF 
 
 ration, the burning of wood and coal for fuel, are 
 attended with the conversion of the free oxygen of 
 the air into carbonic acid. By the putrefactive de- 
 composition of animal and vegetable substances^ 
 poisonous principles, far worse than carbonic acid, 
 are given off into the air. The volcanic vents, so 
 numerous in both eastern and western hemispheres, 
 discharge, as is well known, almost inconceivable 
 quantities of noxious gas, chiefly carbonic acid, even 
 when all traces of heat have disappeared, and no 
 active eruption of lava has occurred within the his- 
 torical period, as in the case of the ancient volcanoes 
 of the Rhine. 
 
 The chief characteristic of the present phase of 
 society, the crowding together of multitudes of men 
 into towns and cities, and their employment in man- 
 ufactures of various kinds, in very many of which 
 gases and exhalations of the worst description are 
 copiously evolved j and even without this, the mere 
 aggregation of such a mass of human beings, each 
 one unconsciously consuming the air of heaven and 
 replacing it by poison, would speedily put a stop to 
 life altogether. If the heavy carbonic acid, so copi- 
 ously generated from these many sources, were sim- 
 ply to obey the natural law of gravitation, and 
 spread itself out upon the surface in such localities, 
 a state of things would arise only now to be paral- 
 leled by the condition of the hold of a slaver. 
 
 This, however, is not all. It has been stated that 
 the atmosphere contains, as a mean, about one part 
 in two thousand by volume of carbonic acid. It 
 may also be shown, without much difficulty, that if 
 
THE EARTH AND ITS ATMOSPHERE. 33 
 
 the whole carbonic acid of the air were collected 
 into a stratum or bed occupying the lower part of 
 the atmosphere, such stratum would have a thick- 
 ness of about thirteen feet. Now let any one who 
 wishes to gain a notion of the effect of such a layer of 
 heavy, irrespirable gas spread over the whole ocean 
 and lower part of the earth, gain admission to one 
 of the large London breweries, and observe a sort of 
 miniature representation of this state of things in 
 the great fermenting vessels, filled to their upper 
 edge with this gas, disengaged during the conversion 
 of sugar into spirit. Let him consider what would 
 be the condition of men, if each continent and island 
 were separated by an invisible ocean of poisonous 
 gas, as impassable as the barrier between the dead 
 and the living, encroaching even upon the land itself, 
 filling the valleys and lower levels, and causing in- 
 stantaneous death to the unfortunate being who 
 should for a moment be plunged beneath its treach- 
 erous surface. 
 
 It may, however, be said, and with great truth, 
 that such a state of things is impossible. Carbonic 
 acid is freely soluble in w r ater ; no reason can be 
 assigned why this power of solution should not be 
 exercised by the water of the sea upon the gaseous 
 stratum above described, the effect of which would 
 of course be its total disappearance, the gas being 
 held in complete solution in the ocean water. Man 
 would then have no reason to dread asphyxia by 
 carbonic acid ; if any creatures suffered, it would be 
 the inhabitants of the water, to whom, in all proba- 
 bility, this great additional quantity of carbonic acid 
 2* 
 
34 ON THE CHEMICAL NATURE OP 
 
 and of carbonate of lime, speedily taken up, would 
 prove highly noxious ; but there is another most 
 important consideration, which must not for a mo- 
 ment be allowed to remain out of sight. 
 
 The dependence of animals for their food upon 
 the vegetable world, is easily seen : where no vege- 
 tation exists, there can be no animal life. Now, as 
 will hereafter be shown, plants in their turn depend 
 in very great measure upon the atmosphere for their 
 sustenance; they get their carbon from the air, by 
 decomposing the carbonic acid it contains. Car- 
 bonic acid, in small quantities for an excess is de- 
 struction is absolutely indispensable to the exist- 
 ence of vegetable life, and if it were withdrawn from 
 the atmosphere in the way supposed, the latter must 
 cease from the face of the globe, and with it vitality 
 altogether. 
 
 Thus it is that, in all the arrangements of the 
 material world whose details science has brought to 
 light, the bodies and agents employed have been so 
 chosen with reference to all their properties and 
 mutual relations, that the slightest imaginable 
 change in the latter may often be strictly shown to 
 be incompatible with the safety and equilibrium of 
 the whole. 
 
 The oxygen and nitrogen, too, instead of being 
 uniformly mixed throughout the whole atmosphere, 
 as at present, having the energetic chemical powers 
 of the one modified and softened diluted, as it 
 were by the other, would form two immense layers 
 of unequal thickness, arranged in the order of their 
 densities, the oxygen below and the nitrogen above. 
 
THE EARTH AND ITS ATMOSPHERE. 35 
 
 In such an order of things as this, animal existence 
 would be out of the question : an atmosphere of pure 
 oxygen is as fatal to life as one destitute of that ele- 
 ment all the phenomena of combustion and oxida- 
 tion generally would be exalted tenfold in power 
 and energy; in fact, the present arrangement of 
 nature could not be maintained in its integrity a 
 single hour. 
 
 The equable diffusion of vapour of water through 
 the atmosphere, is no less important than that of the 
 carbonic acid. In many warm countries, during a 
 great part of the year, rain seldom or never falls, 
 and it is only from the copious dews deposited, in the 
 night that vegetables derive the supply of moisture 
 required for their growth, and to sustain them, by 
 the cooling effects of evaporation, from the scorch- 
 ing rays of the noon-day sun. Were the invisible 
 elastic steam disengaged from the surface of the 
 sea, or other large bodies of water not subject to the 
 diffusive law in question, it is probable that other 
 and very different phenomena would be observed. 
 
 To take another case, not perhaps so striking to 
 the casual observer, but equally important in the 
 eyes of the attentive student. In respiration, the 
 object of which is to bring the blood in contact 
 with the oxygen of the air for the purpose of effect- 
 ing changes hereafter to be described, the lungs are 
 alternately filled and emptied by the mechanism of 
 the respiratory muscles, internal and external, and 
 the air from without thus finds its way into the 
 minute cells which terminate the last ramifications 
 of the bronchial tubes; here its oxygen is made to 
 
36 ON TffE CHEMICAL NATURE OF 
 
 act upon the venous blood, while the latter disen- 
 gages carbonic acid in place of the oxygen absorbed. 
 Now in expiration, even when forced, the lungs are 
 very far from being completely emptied of air, and 
 that which is thrown out is in a great measure de- 
 rived from the larger tubes and passages, the ulti- 
 mate cells in which all the real business is perform- 
 ed, remain filled with the vitiated air which must be 
 displaced, if the function is to be continued, by 
 other means more efficacious than the gentle pres- 
 sure of the elastic thorax. Here it is that diffusion- 
 comes into play between the oxygen of the tubes 
 and the carbonic acid of the cells ; the latter is 
 speedily removed and replaced by the former, and 
 expelled from the body by the next following ex- 
 piration. 
 
 Such, then, are some of the leading consequen- 
 ces which follow from this one single property of 
 gaseous bodies, their difTusibility into each other ; 
 we have seen how essential this property is to the 
 present order of nature, and indeed to our very ex- 
 istence; it is not less pleasing to follow its conse- 
 quences in this more humble office of administering 
 to our happiness and pleasures. 
 
 Who does not inhale with rapture the perfumes 
 of a flower garden when the dews of night, or the 
 refreshing summer shower, have awakened the 
 thousand sweet odours of its fair inhabitants ! The 
 breath of the hawthorn and of the rose have been 
 always one of the most favourite themes of the 
 poet's song ; they have ever been associated with 
 the purest and sweetest imaginings of tenderness 
 
THE EARTH AND ITS ATMOSPHERE. 37 
 
 and affection ; and yet this endless succession of 
 pure and simple pleasures is but a mere consequence 
 of the law which bids a vapour, arising by its own 
 elasticity from a volatile substance, mingle itself 
 with the surrounding air, and extend its influence 
 until its effects become so enfeebled by dilution as 
 to be imperceptible to the sense., 
 
ON THE 
 
 CHEMISTRY OF ORGANIZATION. 
 
 FROM the consideration of the earth and its 
 gaseous envelope, we now turn to the still more 
 interesting subject of the chemical history of its 
 organized denizens. The phenomena of life, both 
 in animals and plants, are the result of a power or 
 force not existing elsewhere, under whose control, 
 growth, or increase of volume and weight, takes 
 place, by the introduction of new matter from with- 
 out, in a very extraordinary manner by the devel- 
 opment, namely, of multitudes of little cells or 
 membranous bladders containing a fluid. These 
 cells become afterwards modified in various ways, 
 but their appearance is always antecedent to the 
 production of circulating vessels, or, indeed, of any 
 of the more complex forms of organic structure. 
 
 The membrane which constitutes the cell-wall is 
 freely permeable by fluids, and consequently, by 
 gaseous matter soluble in those fluids ; food is thus 
 carried into the interior of the mass for the nourish- 
 ment of fresh generations of cellules, each produced 
 from a living point or germ within the substance of 
 a pre-existing cell. 
 
ON THE CHEMISTRY OF ORGANIZATION. 39 
 
 This is all that the microscope makes known to 
 us, and it must be confessed that it is little enough. 
 
 The most wonderful property of the living cell 
 is its power of influencing chemical action ; what 
 is called " secretion" in animals and plants is the 
 result of the exercise of this function ; growth it- 
 self is a consequence of it, for the cell secretes or 
 prepares its own food. And what is still more as- 
 tonishing, different kinds of cells possess different 
 powers in this respect; one shall decompose car- 
 bonic acid, reject the oxygen, and unite the carbon, 
 so eliminated, to the elements of water ; a second 
 shall produce, out of the inorganic constituents of 
 the air, the odoriferous principle of the rose ; a third 
 shall convert the albumen of the blood into the azo- 
 tized principle of milk ; and yet to the eye all are 
 alike all little wet bladders ! 
 
 It is in the vegetable world that the formative 
 power of this extraordinary agent is most evident 
 in the generation, out of purely inorganic matter, 
 of all the substances visible in the plant itself. 
 Every green leaf, every part which can perform the 
 duty of a leaf, is the theatre of these wonderful 
 events these strange decompositions which we can- 
 not imitate. 
 
 In an animal, however, the case seems different ; 
 the vital force is, in some measure, occupied in shield- 
 ing from decay the fabric of the body. The chem- 
 istry of life is not here of so lofty and subtle an 
 order as in the plant ; it is confined to the modifica- 
 tion, the change of complex organic principles 
 already existing principles which, as we shall see, 
 
40 ON THE CHEMISTRY 
 
 owe their origin to plants. A building up, an or- 
 ganizing power, is indeed manifest ; but the mate- 
 rials are furnished, as it were, to its hand, in a state 
 requiring, at the utmost, an exertion of chemical 
 force infinitely less energetic than that required to 
 produce woody fibre, or sugar, from carbonic acid 
 and water. 
 
 It will be convenient, therefore, for the present, 
 at least, to admit the existence in plants and animals 
 of a peculiar power, which we may call "vital 
 force," distinct from ordinary chemical attraction, 
 but having relations with the latter, as close and in- 
 timate as those which connect chemical and electri- 
 cal phenomena. 
 
 There is, perhaps, at the present moment, no de- 
 partment of natural science which offers so rich a 
 reward to patient and diligent investigation, as the 
 chemical study of the almost endless series of proxi- 
 mate organic principles formed by the union in va- 
 rious ways among themselves, of the four elementary 
 bodies, carbon, hydrogen, oxygen, and nitrogen. It 
 cannot fail to excite the attention of the most super- 
 ficial observer, to discover that substances possessing 
 properties of the most opposite kind should be made 
 up of the very same materials that the sweet crys- 
 tallizable principle of the sugar-cane, the bitter febri- 
 fuge of the willow-bark, the fixed and permanent 
 acid of the grape, the highly volatile acid of vine- 
 gar, and many other equally well-contrasted sub- 
 stances should be composed of the same three ele- 
 mentary bodies, carbon, hydrogen, and oxygen, 
 merely differing slightly in the proportions in which 
 
OF ORGANIZATION. 41 
 
 they are associated. A very few grains of the vege- 
 table alkali morphia, or a fraction of a grain of ano- 
 ther member of the same chemical family, strychnia, 
 will destroy life; the bread we subsist upon owes its 
 nutritious power to a combination of the very same 
 elements which, in other circumstances, give origin 
 to the poisonous juice of the poppy, or the still more 
 deadly principle of the mix vomica. The slightest 
 difference in the relative proportions of the constitu- 
 ents of such compounds may give rise to the utmost 
 conceivable discrepancies in their chemical relations. 
 
 This, however, is not all ; it has long and justly 
 been held a kind of axiom in chemistry, that the 
 " same chemical compound must always contain the 
 same elements, united in the same proportions." 
 The converse, however, to this proposition is not 
 true; two or more bodies uniting, in constant pro- 
 portions, do not of necessity generate the same sub- 
 stance. We may have, not merely two, but a whole 
 series of compounds, differing as much from each 
 other in all respects, chemical and physical, as the 
 imagination can conceive, and yet one and all be 
 made up of the same elements, joined together in the 
 same proportions. 
 
 This most curious and unexpected discovery was, 
 at first, and very properly, received with doubt and 
 distrust, as a false result, due to inaccurate research, 
 and it was thought that, as practical analysis became 
 more strict, differences of composition would be 
 found in these cases, fully adequate to account for 
 the discrepancies of characters observed. This an- 
 ticipation, however, has not been verified: within 
 the last few years organic chemistry has made vast 
 
42 ON THE CHEMISTRY 
 
 advances in every department of the science ; the 
 analytical methods of research have been greatly 
 simplified, and increased in delicacy; but instead of 
 a refutation of the new doctrine, by appeal to more 
 exact experiments, it has been strengthened and ex- 
 tended by almost every labourer in this fertile field. 
 The number of" isomeric bodies," as these are called, 
 where identity of composition is associated with di- 
 versity of qualities, is at the present moment very 
 great, and every year increases their number ; they 
 are to be found in nearly every section of the sci- 
 ence, and constitute its most striking and character- 
 istic feature. 
 
 Here, again, is another illustration of the truth 
 of the remarks already made respecting the very 
 peculiar nature of the four ultimate organic ele- 
 ments. It is not denied that cases occur in mineral 
 chemistry which seem to be the analogs of the iso- 
 meric substances of the organic world,* but these 
 are few and far between, and would, perhaps, have 
 escaped notice altogether had not attention been 
 strongly excited by the discoveries just mentioned. 
 
 An attentive study of the chemical history of the 
 proximate organic principles will soon raise in the 
 observer a conviction of the great and essential dif- 
 ference in constitution and structure, so to speak, 
 between these bodies and the salts and oxides, and 
 other compounds of inorganic chemistry. As some 
 importance is attached to such distinction, it may not 
 be improper to discuss it in sufficient detail to ren- 
 
 * Phosphoric acid ; perhaps chromic acid, and one or two 
 other bodies. 
 
OF ORGANIZATION. 43 
 
 der it intelligible to the reader whose knowledge of 
 elementary chemistry is but slight. 
 
 In all the combinations of the metals and non- 
 metallic substances, the investigation of which con- 
 stitutes mineral or inorganic chemistry, a principle, 
 or mode of union, is every where found to prevail, 
 which we may term the " binary" mode of combi- 
 nation. This is sufficiently easy to understand, if 
 we consider one or two cases, which may be taken 
 as types or representatives of the rest. The very 
 familiar salt, alum, we have every reason, at the 
 present moment, to consider as a direct compound of 
 two other saline substances namely, sulphate of 
 alumina and sulphate of potash. Each of these in 
 its turn is generated by the union of a pair of bodies 
 sulphuric acid and alumina on the one hand, and 
 sulphuric acid and potash on the other. These are, 
 however, themselves compounds. The acid is an 
 oxide of sulphur, the bases are the oxides of the two 
 metals aluminium and potassium. 
 
 Perhaps the following diagram will give an idea 
 of the successive steps of pairing in the formation of 
 a complex inorganic substance like alum, first, be- 
 tween acknowledged elementary bodies ; then, be- 
 tween compounds of the first order ; and, lastly, 
 between two complete oxygen-acid salts: 
 
 Crystallized Alum. 
 
 Alum. Water. 
 
 I I 
 
 Sulphate of Alumina, Sulphate of Potash. Hydrogen. Oxygen. 
 
 "--'-' ' ' " Potash. Sulphuric Acid. 
 
 Aluminium. Oxygen. Sulphur. Oxygen. Potassium. Oxygen. Sulphur. Oxygen. 
 
44 ON THE CHEMISTRY 
 
 There is a curious salt now used in the arts for 
 tinning and soldering copper, or rather for assisting 
 in these processes. It is made by mixing together 
 solutions of sal-ammoniac and of chloride of zinc in 
 certain proportions, and evaporating down the liquid 
 until the new body separates in crystals on cooling. 
 This substance consists of chlorine combined with 
 zinc, and with the radical or basis of the salts of am- 
 monia. We do not, however, for a single instant, 
 imagine that, in this, or any analogous case in inor- 
 ganic chemistry where three bodies are concerned, 
 union among them occurs in any other way than in 
 that described namely, in dividing one between the 
 other two, thus generating a pair of binary compounds, 
 which, by uniting in their turn, give origin to the 
 body itself. In the example cited, the salt in ques- 
 tion, the " chloride of zinc and ammonium," is look- 
 ed upon as a true double salt formed by the union 
 of a pair of chlorides ; and this view of the matter is 
 supported by direct experimental evidence of unques- 
 tionable weight and authority. 
 
 Such, then, is the great characteristic feature of 
 all inorganic combinations progressive union of 
 pairs of substances, simple and compound. The case 
 of the proximate organic principles, to the consider- 
 ation of which we must now return, is strikingly 
 different. 
 
 In the majority of these substances we find the 
 three or four elements so often mentioned carbon, 
 hydrogen, oxygen, and nitrogen associated in a way 
 quite new and peculiar, a fashion of union altogeth- 
 er different from the binary or inorganic type ; in 
 
OF ORGANIZATION. 45 
 
 accordance with a plan, in short, which is unknown 
 in the other division of the science. Instead of com- 
 bination by pairs, we see three or four substances 
 bound up together in a single group, constituting one 
 indivisible whole, susceptible of entering into combi- 
 nation, and being thence disengaged and set free with- 
 out change or alteration. For example, one of the 
 most familiar substances of daily life, sugar, is a true 
 chemical compound of carbon, hydrogen, and oxy- 
 gen, in which the two last named elements exist in 
 such proportions, that if they were united they would 
 form water. Hence sugar is said to consist of carbon 
 and the elements of water; and some have even gone 
 the length of supposing it really to contain water 
 itself, ready formed, to be in short a" hydrate of car- 
 bon ;" but this idea is unsupported by the evidence, 
 which leads to a conclusion altogether different 
 namely, that the sugar is, as already stated, a direct" 
 combination of the three elementary bodies. 
 
 We thus get acquainted with quite a new class 
 of substances a set of ternary and quaternary com- 
 pounds, which may be expected to possess characters 
 and properties quite peculiar; and this is really 
 found to be the case. It is well worthy of observa- 
 tion also, that the organic type spoken of is very 
 often obstinately retained even after the vegetable or 
 animal principle has been subjected to very impor- 
 tant modifications by powerful chemical re-agents. 
 The stamp of vital origin ofte n resists for a long 
 time the means taken to destroy it, and the result is 
 very frequently the production of an extended ser ies 
 
46 ON THE CHEMISTRY 
 
 of curious products in a kind of descending scale, 
 gradually decreasing in complexity of composition. 
 
 When sugar is placed in particular circumstan- 
 ces, hereafter to be noticed, it undergoes conversion 
 into alcohol or spirit of wine, carbonic acid be- 
 ing at the same time produced. This alcohol is a 
 true ternary substance like sugar itself, but simpler 
 in constitution. Again, alcohol is freely convertible 
 into acetic acid by the loss of some of its hydrogen, 
 and the acquisition of oxygen in its place. Acetic 
 acid, in its turn, can be decomposed by appropriate 
 methods, and made to furnish a third ternary sub- 
 stance still less complex namely, pyroacetic spirit or 
 acetone. This is an example of a succession of three 
 descending steps, through which a complex organic 
 compound may be made to pass without losing the 
 peculiar and 6haracteristic features of its origin ; 
 and it would be very easy to adduce many more. 
 The animal principle, uric or lithic acid, one of the 
 most interesting bodies in existence, may be made to 
 furnish a most remarkable and very numerous family 
 of new substances, each of which is a true organic 
 principle, although not always directly found in 
 either the vegetable or animal kingdom. Indeed, 
 by far the greater number of objects included within 
 the domain of organic chemistry are bodies formed 
 in this half-artificial manner from the educts, as they 
 are sometimes called, of organization, the direct 
 results of the chemistry of life. 
 
 A very important consequence of the ternary or 
 quaternary structure of organic bodies in general 
 
OF ORGANIZATION. 47 
 
 above described, is the weakness and instability 
 "which result from such an arrangement. It is easy 
 to see, in some measure, the reason of this. If an 
 inorganic substance, even of highly complex nature, 
 be attentively considered, it will be observed that 
 the arrangement of elements is usually such as to 
 give rise to a condition of stable equilibrium, to sat- 
 isfy, as it were, in the fullest possible manner, all the 
 chemical appetites or tendencies of the elements con- 
 cerned. In the case of the alum, for example, the 
 two metals, the hydrogen and the sulphur, are al- 
 ready united to as much oxygen as they have, under 
 the circumstances, any atttraction for. The same 
 is true of the compounds so generated, each base be- 
 ing associated with just so much acid as it requires 
 to form a definite compound ; no cause of decompo- 
 sition exists capable of bringing about a change, 
 short of external agency sufficiently potent for the 
 purpose. 
 
 Contrast this with an organic principle sugar, 
 or acetic acid to take a simple case ; and as we 
 have ventured to represent the constitution of an in- 
 organic compound, let us do the same now with one 
 of the'second kind : let us represent our ternary sub- 
 stance after the following manner, by way of dis- 
 tinction 
 
48 ON THE CHEMISTRY 
 
 and consider what must of necessity take place. 
 The oxygen and hydrogen tend in the strongest man- 
 ner to unite, and form water ; they are prevented 
 from doing so by the attraction of the carbon for 
 both of them individually, while for their compound, 
 water, that element has no apparent affinity what- 
 ever. The same is true of the other possible direct 
 combinations ; carbon and hydrogen, carbon and 
 oxygen, possess mutual attractive powers, but union 
 between them is impossible so long as the opposing 
 force of the third element exists in sufficient inten- 
 sity. 
 
 The state of equilibrium of forces in such a body 
 must be very different from that in one of the inor- 
 ganic substances formerly referred to ; it must be far 
 weaker, and more subject to derangement. The 
 elements are held together by a kind of balance of 
 opposite attractions, and remain united only while 
 that balance is exactly maintained. A small exter- 
 nal disturbing force a slight alteration in the inten- 
 sities of the attractive forces themselves, and the 
 combination is broken up the liberated elements 
 arranging themselves in another and more stable 
 order, giving rise to one or more new bodies. 
 
 In fact, the organic principles for the most part 
 seem to owe what permanence they possess more to 
 some vis inertia than to any inherent strength of 
 their own. They have been produced, in the first 
 instance, under the immediate influence of vegetable 
 life, in circumstances which we cannot imitate, and, 
 in. fact, do not understand ; and they only maintain 
 their integrity afterwards in the absence of disturb- 
 
OP ORGANIZATION. 49 
 
 ing causes. They contain within themselves the 
 principle of their own dissolution, ready to be called 
 into activity by the slightest apparent cause. 
 
 It must not be imagined that the bodies in ques- 
 tion are all equally weak and instable in constitution ; 
 the differences among them in this respect are very 
 striking and well marked, and serve to bear out and 
 confirm in the strongest manner the truth of the 
 principle attempted to be laid down. We find, as a 
 general rule, that those compounds are most prone 
 to rapid and facile decomposition which contain the 
 greatest number of elements, and the most complex 
 arrangement of these elements; while, on the other 
 hand, there are organic bodies so permanent in their 
 nature, and so little subject to change, from simpli- 
 city of constitution, as to approximate in their char- 
 acters to mineral substances, and often form, in fact, 
 *a kind of connexion between the two great sections 
 of chemical science. As examples of such, may be 
 noticed oxalic acid, cyanogen, ferro and sulpho-cy- 
 anogen, and many of their derivatives; certain hydro- 
 carbons, &c. 
 
 There is a physical*character which will some- 
 times aid us in giving a good guess as to the simple 
 or complex constitution of an organic substance 
 the faculty of crystallization. It is not meant to be 
 affirmed that this character is, in all cases, implicit- 
 ly to be relied on, but simply that it is highly use- 
 ful in practice, and has certainly some intimate con- 
 nexion with the molecular structure of bodies. 
 
 This power of assuming tin solidification a dis- 
 tinct and often very characteristic geometrical form, 
 3 
 
50 ON THE CHEMISTRY 
 
 appears to be possessed by all chemical compounds 
 of definite and constant composition, with the excep- 
 tion of a certain number, principally to be found in 
 the class of organic substances of the most complica- 
 ted and instable chemical nature. We know noth- 
 ing, and apparently at present can know nothing, of 
 the ultimate structure of any substance whatever, 
 but it is not difficult to figure to one's self some idea of 
 the gradual weakening of the molecular forces, 
 upon which crystallization depends, whatever the 
 nature of those forces maybe, by an increase in their 
 number and in the multiplicity of directions in which 
 the forces themselves are exerted. 
 
 It very often happens that, in these cases where 
 crystalline texture is altogether absent, we observe 
 in its place an appearance of a very different kind ; 
 we notice that the smallest particles of matter which 
 can be traced by the microscope exhibit a rounded 
 or globular figure instead of the straight lines and 
 angles of the crystallizable compounds. These 
 very frequently appear to aggregate together in 
 strings or rows, not altogether unlike some of the 
 very lowest structures of the vegetable world, where 
 a commencement of organization is, as it were, just 
 visible. The substances forming the chief constitu- 
 ents of the animal body are in this condition ; these 
 are, it is certain, the most highly complex of all 
 chemical compounds known, and the most subject 
 to rapid and destructive change, as we shall hereaf- 
 ter have an opportunity to see. 
 
 It would be easy to extend these observations 
 much further, but it is hoped that enough has been 
 
OF ORGANIZATION. 51 
 
 said to establish the proposition that " the selection 
 out of the whole number of elementary substances of 
 the four organic elements carbon, hydrogen, oxy- 
 gen, and nitrogen for the purposes of organization, 
 was expressly made from a full previous knowledge 
 of the very extraordinary chemical properties possess- 
 ed by these substances by which they alone are fit- 
 ted for the objects intended." Design, therefore, is 
 proved. 
 
VEGETABLE CHEMISTRY. 
 
 THE proximate organic principles already known 
 and examined, directly derived from plants, are very 
 numerous, and every year adds to the list and to our 
 knowledge respecting them. The majority of these, 
 however, are bodies which occur in very minute quan- 
 tity in certain particular vegetables ; and although 
 highly interesting to the scientific chemist on account 
 of their curious properties, and important to mankind 
 in general from the powerful medicinal virtues they 
 often possess, form too small a portion of the body 
 of the vegetable in which they occur to require a 
 lengthened description in a treatise where the object 
 is more to give an idea of the general functions in 
 Nature of the chemical elements on the great scale, 
 than to impart specific information concerning indi- 
 vidual substances and their relations, which may be 
 learned by consulting any one of the several excel- 
 lent elementary works on chemical science which 
 now exist, both in our own language and in those 
 of the Continent. 
 
 There are, however, some few of these bodies so 
 
VEGETABLE CHEMISTRY. 53 
 
 universally diffused through the whole vegetable 
 world, and so important and valuable in every re- 
 spect, that it is indispensable to make some ac- 
 quaintance with them before entering upon the some- 
 what difficult subject of the food of plants. 
 
 We shall take them in the order found most con- 
 venient in this study. 
 
 The proximate vegetable principles may be di- 
 vided into two classes namely, those containing 
 nitrogen, and those destitute of that element. It 
 will be convenient to consider the latter division 
 first. 
 
 The principal groups of substances contained in 
 this section are the following : 1. Saccharine and 
 amylaceous bodies. 2. Vegetable acids. 3. Fatty 
 and resinous principles. 
 
 THE SWEET PRINCIPLES OF PLANTS seem to be rather 
 numerous ; already five or six distinct bodies of this 
 kind have been pointed out and examined, and it is 
 probable that others exist which are yet undescribed. 
 Thus, one particular kind of sugar abounds in the 
 juice of the sugar-cane, in beet-root, and parsnips ; a 
 second constitutes the sweet matter of all ordinary 
 fruits ; a third is found in certain fungi ; a fourth in 
 the common liquorice; a fifth exists in manna, which 
 is an exudation from a species of asb,fraxinus ornus y 
 common in southern Europe ; the eucalyptus-sugar 
 of Van Dieman's land, recently described by Profes- 
 sor Johnston, probably belongs to the last-named 
 modification.* 
 
 * Memoirs of Chemical Society of London, vol. i. p. 159, 
 
54 VEGETABLE CHEMISTRY. 
 
 All these substances closely resemble each other 
 in many points, while at the same time sufficient dif- 
 ference of character exists among them to establish 
 their separate identity. Manna-sugar exhibits the 
 least agreement with the rest of the group in its 
 composition and properties. 
 
 The two modifications of the sweet principle first 
 mentioned namely, the sugar of the cane and the 
 sugar of fruits, or, as it is commonly called from its 
 most abundant natural source, the sugar of grapes, 
 alone possess sufficient interest and importance to 
 require description. 
 
 The first of these, an article of luxury rendered 
 by habit almost a necessary of life to every class of 
 the community, is prepared in enormous quantities 
 from the juice of the sugar-cane in most of the 
 warmer regions of the earth where the climate ad- 
 mits of an advantageous cultivation of that plant. 
 The tropical colonies of Great Britain alone furnish 
 an immense supply of this now indispensable article. 
 In France, and elsewhere on the continent of Europe, 
 sugar, identical with that of the cane, is manufactured 
 from beet-root on a scale of considerable magnitude, 
 but the process is, in this case, much more trouble- 
 some from the greater proportion of impurities in 
 the juice of the latter. 
 
 The meadow grasses of our own country contain 
 a sweet substance, occasionally in some abundance, 
 which may very possibly be ordinary cane-sugar, 
 and it is to this that much of the value of these 
 plants as food for cattle may fairly be attributed. 
 
 Although the theory of the sugar manufacture is 
 
VEGETABLE CHEMISTRY. 55 
 
 simple enough, the practice is beset with difficulties 
 and attended with loss and injury of material arising 
 from the extreme susceptibility of change of the 
 cane-juice itself. The latter, as it runs from the 
 crushing-mill, is as clear and nearly as colourless as 
 water; but a very short exposure to the atmosphere, 
 in those warm regions, suffices to set up a com- 
 mencement of decomposition which rapidly ad- 
 vances, and in a short time converts the sweet- 
 tasted bland liquid into a spirituous or ascescent pro- 
 duct, turbid from insoluble suspended matter, and 
 totally unfit for the purpose to which it was intended 
 to be applied. To guard against this evil, the sugar- 
 boiler always endeavours to conduct the first part, at 
 least, of his process as rapidly as possible ; he heats 
 the freshly expressed juice in a large vessel to near 
 the boiling point, having previously added a little 
 slaked lime to neutralize a small portion of free acid 
 always present in the liquor, the effect of which in 
 the after part of the operation is very pernicious. 
 By this proceeding a solid flaky substance, the na- 
 ture of which will shortly be mentioned, separates, 
 and the clear liquid being removed by a syphon or 
 otherwise, is rapidly evaporated down in open pans, 
 until the syrup becomes strong enough to yield crys- 
 tals of sugar after cooling. 
 
 The product of this operation is the crude or 
 muscovado sugar of commerce ; this is seen on close 
 inspection to consist of small but distinct crystals of 
 sugar, stained and rendered impure by dark-coloured 
 uricrystallizable syrup or molasses, which latter sub- 
 stance does not pre-exist in the juice of the cane, 
 
56 VEGETABLE CHEMISTRY. 
 
 but is produced at the expense of some of the crys- 
 tallizable sugar by the high temperature used in the- 
 concentration of the saccharine solution. Raw beet- 
 root sugar is a far worse article than that from the 
 cane, and is, indeed, almost unfit for use until refined. 
 The refining process is as simple as the original 
 manufacture : the operator makes choice, if circum- 
 stances permit, of what he calls a strong sugar, that 
 is large in the grain, very distinctly crystalline, not 
 caring so much about the colour, which he has it in 
 his power to remove ; he dissolves this in water, 
 mixes it with albumen, white of eggs, or serum of 
 blood, and heats the whole to ebullition, by which 
 the albumen is coagulated, and certain mechanical 
 impurities removed with the coagulum from the 
 liquid. The next point is to whiten or decolorize 
 the syrup, which is done by filtering it through a 
 bed of coarsely-powdered animal charcoal, which 
 possesses the singular property of absorbing various 
 organic colouring matters ; it comes through very 
 nearly colourless, and only requires to be concentrated 
 by evaporation to yield pure sugar. In the best 
 refineries this evaporation, instead of being con- 
 ducted at a high heat in open vessels whereby a 
 second loss from the formation of uncrystallizable 
 syrup, besides an increase of colour in the whole pro- 
 duct, would infallibly ensue is carried on in strong 
 metallic boilers, or stills, of peculiar construction, 
 exhausted of air by a powerful engine. By this 
 diminution of pressure on the liquid, its boiling point 
 is reduced to about 150 F. 5 and all blackening pre- 
 vented. 
 
VEGETABLE CHEMISTRY. 57 
 
 In the western parts of North America, an excel- 
 lent sugar is extracted from one of the maples the 
 acer saccharinum, common in those parts. The tree 
 is tapped, in the spring, by boring an auger-hole a 
 little way into the wood, and the juice collected in 
 a vessel below, and evaporated in a common iron 
 pan to the requisite density for crystallization. This 
 sugar, which is an article of great value to the in- 
 habitants, is chiefly employed by them for domestic 
 uses, very little being exported. 
 
 In white candy or the finest loaf-sugar, we have 
 the substance in a state of very high chemical purity, 
 the only difference between them being the same as 
 that seen on contrasting calcareous spar with white 
 marble ; the one exhibits large and distinct crystals, 
 the other a confused assemblage of small ones. 
 
 The most obvious properties of this very inter- 
 esting substance, its free solubility in water, pure 
 sweet taste, and other evident characters, are too 
 familiar to every one to need notice here ; its rela- 
 tions will be discussed in conjunction with those of 
 the other members of the great series to which it 
 belongs. 
 
 SUGAR OF GRAPES, the ordinary sweet principle 
 of ripe fruits. 
 
 This variety of sugar may be obtained in large 
 quantity from the sources above mentioned, by a 
 proceeding very similar to that by which ordinary 
 sugar is extracted from the cane. We possess, more- 
 over, the power of artificially producing this sub- 
 stance by a modification of the two next bodies to 
 be described, starch and woody fibre. 
 3* 
 
58 VEGETABLE CHEMISTRY. 
 
 Grape-sugar is easily to be distinguished from 
 the other kinds; it crystallizes from its watery solu- 
 tion slowly and with some difficulty, while the crys- 
 tals thus obtained are very confused and indistinct, 
 and rarely exhibit brilliant faces. It is much less 
 soluble than cane-sugar, and very inferior in sweet- 
 ness, which latter circumstance interferes with its 
 application to economical purposes. Grape-sugar is 
 further distinguished by its behaviour with respect to 
 heat, and various energetic chemical agents, acids 
 and alkalis. It seems to be, upon the whole, a much 
 more stable and permanent substance than the va- 
 riety first discussed, and most probably has a simpler 
 chemical constitution. 
 
 STARCH, OR FECULA, is a body of great interest 
 in many respects, from its universal occurrence in 
 the vegetable kingdom, the important objects it there 
 fulfils, and, lastly, the curious changes it may be 
 made to undergo in the hands of the chemist. 
 
 There is scarcely a plant, or part of a plant, 
 which, when closely examined, does not yield more 
 or less of this substance ; not unfrequently the quan- 
 tity is so great as to produce in the plant the appear- 
 ance of deformity by enormous distention of the cel- 
 lular tissue in which the starch is contained. We 
 have examples of this in the common potato, a fleshy, 
 under-ground stem, bearing buds upon its surface, 
 but swollen out of all shape and figure by an accu- 
 mulation of starch mingled with water within each 
 individual cell: in the roots of certain orchideous 
 plants, and in very many others where a soft and 
 succulent character is observed ; the plant which 
 
VEGETABLE CHEMISTRY. 59 
 
 furnishes arrow-root, a mere variety of starch, is a 
 case of the kind; the interior of the stems of many 
 palms is often filled with loose cellular substance, 
 rich in starch ; and, lastly, it constitutes a very im- 
 portant, and often very abundant, ingredient in seeds 
 of all kinds. 
 
 The simplest and most expeditious method of ob- 
 taining this principle is perhaps the following: 
 potatoes after being pared are grated or rasped to a 
 pulp; this pulp is put upon a sieve, antf stirred 
 about, while at the same time a little stream of wa- 
 ter is made to flow upon it. A milky liquid runs 
 through the sieve, and may be received in a basin 
 beneath ; this, after a few minutes' rest, deposits a 
 white powder, which is the starch itself. By this 
 simple mechanical process of tearing up the vegeta- 
 ble tissue, and removing the enclosed starch by 
 washing, that substance may be got from a great 
 variety of plants, although not always with equal 
 facility. 
 
 Starch is insoluble in cold water, as the above 
 mode of preparation necessarily implies. It presents 
 to the naked eye the aspect of a white powder, hav- 
 ing sometimes a brilliant silky lustre, which, under 
 the microscope, is too remarkable in its appearance 
 to fail in arousing the attention of the observer. By 
 an instrument of good power, it is seen to consist 
 of a multitude of little transparent rounded grains, 
 quite destitute of crystalline structure, but present- 
 
60 VEGETABLE CHEMISTRY. 
 
 ing, on the contrary, traces 
 of an organized arrangement, 
 giving the idea of little eggs 
 or seeds. A dark spot, or 
 " hilum," is seen at one ex- 
 tremity, surrounded by a num- 
 ber of parallel rings or striaB, 
 which cover the whole surface 
 of the granule, and seem to be 
 depressed or cut into it. 
 The magnitude of these starch granules is very 
 different in various plants ; in the potato they are 
 often very large, about - 2 * of an inch in diameter; 
 in arrow-root considerably smaller, while in the 
 fecula from the grain of the cereals, they are very 
 small indeed. The size and appearance of the 
 granule afford almost the only method of distinguish- 
 ing one variety from another. 
 
 When- starch is put into cold water and gently 
 heated, a change takes place by which the proper- 
 ties of the substance are completely altered. At a 
 temperature a little short of the boiling point of wa- 
 ter, the granules break or burst, and their contents 
 are acted upon, giving rise to a nearly transparent 
 gelatinous mass, freely miseible with water, if not 
 really dissolved in that liquid, and in which floafe 
 about numerous minute shreds of membranous mat- 
 ter, easily discovered by the microscope. Now, 
 there is some diversity of opinion respecting the real 
 structure of starch, and the nature of the change it 
 undergoes by the action of hot water ; the most 
 probable explanation seems to be that the grains 
 
VEGETABLE CHEMISTRY. 61 
 
 consist of a soluble matter enveloped in a fine mem- 
 brane, which is rent, or otherwise destroyed, at a 
 high temperature, and the internal substance attack- 
 ed ; so that each granule must be looked upon as an 
 organized membranous cell, filled, like the fat-cells 
 of the animal body, with a peculiar matter, itself al- 
 together destitute of organization, and, in fact, a 
 mere chemical compound ; we may call it, for the 
 sake of distinction, " amidine," or gelatinous starch. 
 This view is strengthened by the following fact : 
 amidine is destitute of nitrogen ; it contains nothing 
 but carbon, hydrogen, and oxygen ; now starch, 
 analyzed as a whole, always gives a little nitrogen, 
 which may reasonably be supposed to rise from the 
 organized integument, such structures in plants, as 
 well as in animals, often containing nitrogen as an 
 essential component. It is unwise, however, to give 
 a decided opinion on this subject ; the phenomena 
 observed by several recent experimenters, are very 
 curious, and not easy to reconcile to this simple 
 view.* 
 
 When thick gelatinous starch is boiled for a few 
 minutes with dilute acid of almost any Kind, a little 
 weak sulphuric acid for example, it undergoes 
 another remarkable alteration j from a viscid mass 
 it changes to a fluid as limpid as water, and if the 
 acid be now withdrawn by saturation, and the 
 liquid gently evaporated to dryness, it furnishes a 
 substance having many of the characters of gum, 
 but differing in some respects from that substance. 
 
 * See papers of MM. Payen and Jaquelain, in the Annales 
 de Chimie et de Physique. 
 
62 VEGETABLE CHEMISTRY. 
 
 To this new body the name " dextrine," or gummy 
 starch, has been given ; its chemical composition is 
 exactly the same as that of gelatinous starch. 
 
 If, now, instead of interrupting the ebullition as 
 soon as the mixture has become thin and clear, 
 we continue it for the space of several hours, 
 adding from time to time small quantities of water, 
 to supply the place of that lost by evaporation, and 
 then separate the acid by chemical means, and boil 
 down the clear solution to a small bulk, we get a 
 syrupy liquid, very sweet to the taste, which, on 
 standing for a few days, entirely solidifies to a mass 
 of grape-sugar, exceeding in weight the starch from 
 which it was produced. 
 
 In these curious transformations, the acid em- 
 ployed undergoes neither change nor diminution. 
 It is all withdrawn in its original amount after the 
 experiment ; nothing is absorbed from the air, and 
 no other substances but dextrine or grape-sugar 
 generated ; and a reference to the chemical com- 
 position of the substance employed, and that ob- 
 tained, easily shows that the whole affair lies, in 
 fact, between the amidirie and the elements of 
 water, grape-sugar containing more oxygen and 
 hydrogen, compared with the quantity of carbon, 
 than starch. 
 
 Such is a brief notice of this extraordinary 
 change, in which common potato-starch may, at 
 pleasure, be made to yield more than its own weight 
 of sugar of grapes. There are, however, other 
 methods by which the same end may be effected. 
 If a little common malt, barley made to germinate, 
 
VEGETABLE CHEMISTRY. 63 
 
 be roughly powdered and infused in tepid water, a 
 solution is obtained which exhibits the same power 
 as the dilute acid of converting a large quantity of 
 thick starch first into dextrine, and finally into sugar. 
 It is sufficient, in order to show this fact, to mingle 
 some gelatinous starch with a small quantity of in- 
 fusion of malt, and expose the whole to a gentle 
 heat, not exceeding 160 F. In a very few minutes 
 it becomes thin like water ; and if the temperature 
 be kept up during three or four hours, the liquid be- 
 comes sweet to the taste, and is then found, on ex- 
 amination, to be rich in grape sugar. 
 
 The conversion of the starch into sugar is sup- 
 posed, in this case, to be due to the presence of a 
 substance in the malt, or germinated grain, called 
 " diastase," imagined to exist in all seeds under simi- 
 lar circumstances, in active buds, and probably else- 
 where. Attempts made to isolate this curious body 
 have not been very successful. So far as is known, 
 it seems to belong to the class of vegetable albumi- 
 nous principles a class of substances second to 
 none existing in importance to the economy of or- 
 ganization, as we shall have occasion to see. The 
 quantity of diastase necessary to effect the above- 
 described metamorphosis is very small. Its action, 
 although most energetic at a moderately high tem- 
 perature, is said to be still perceptible at a much 
 lower one, even that of the air. A boiling heat an- 
 nihilates its specific po\ver by causing coagulation 
 and insolubility. 
 
 These remarks will suffice to render to a certain 
 degree intelligible the beautiful order of arrange- 
 
64 VEGETABLE CHEMISTRY. 
 
 ments by \vhich plants are furnished with a sudden 
 and copious supply of already assimilated food at 
 certain particular periods of their life, when the 
 drain upon the natural powers is excessive, or when 
 the plant, from its feeble and undeveloped state, is 
 unable to obtain and digest food from without. 
 Every one is familiar with the fact, that a very large 
 proportion of the vegetable inhabitants of the tem- 
 perate zones, at the close of every summer, either 
 perish completely, or die down to the roots, which 
 remain in the ground until the following spring. It 
 is not uncommon to attribute this effect to the in- 
 creasing coldness of the season to the nipping frosts 
 of the fine clear autumn nights. A far more efficient 
 cause is, however, to be found in the plant itself, 
 whose death is the result of the exhausting nature 
 of the process by which provision is made for ano- 
 ther generation of similar beings. The periods of 
 inflorescence and seed-bearing are attended with a 
 large expenditure of costly material. The develop- 
 ment of a flower is a very different affair to that of 
 a green leaf. The former contributes nothing to 
 the general maintenance of the plant ; while the 
 latter is at once a new mouth, and stomach, and lung, 
 capable of contributing its share to the general good. 
 In the formation of the fruit and seeds, also, soluble 
 gummy and saccharine matters are conveyed to 
 these points and there fixed, to the manifest detri- 
 ment of the whole system, which suffers by the 
 withdrawal of these substances. Now, it is to guard 
 against, or at any rate to diminish, these evil conse- 
 quences of a necessary functionj that Nature usually 
 
YEGETABLE CHEMISTRY. 65 
 
 employs the time previous to flowering, when the 
 vegetative power is most active, in storing up, in 
 different parts of the plant, a quantity of starch, 
 ready for use when the pressing occasion arrives, at 
 which time it is re-dissolved, by the aid of diastase 
 or some similar substance perhaps, and once more 
 added to the general stock of nutriment. There is 
 reason to think, that were it not for this contrivance 
 the maturation of seeds could hardly take place. 
 As it is, the latter process is no sooner completed 
 than the plant exhibits every sign of exhaustion, 
 and in very many cases dies altogether. The starch, 
 thus transferred from the parent plant to the seed, 
 remains unaltered sometimes for years, until exter- 
 nal causes arouse into activity the vital energies of 
 the germ. The development of the latter com- 
 mences while the starch, slowly passing into a solu- 
 ble state, furnishes, in conjunction with the albumi- 
 nous portion, a constant and ready supply of food, 
 until the radicle and leaves are sufficiently advanced 
 to exercise vigorously their specific functions. 
 
 The conversion of starch into gummy matter and 
 sugar, and that of the latter again into starch, seem 
 to be very common in the vegetable kingdom. It 
 has been shown, for instance, that in the ripening 
 of fruits, such as apples and pears, starch first depos- 
 ited disappears, and sugar is found in its place. Many 
 of these phenomena are at present very imperfectly 
 understood. Enough has, however, already come 
 to light to exhibit to the patient and attentive ob- 
 server glimpses, as it were, of a general design of 
 
66 VEGETABLE CHEMISTRY. 
 
 the most surpassing beauty of contrivance ; and we 
 have good hope that the unprecedented progress 
 which chemistry and the allied sciences are now 
 making, will, ere long, render much clear and intel- 
 ligible which is now dark and perplexed. 
 
 WOODY FIBRE LIGNIN. By this expression is 
 meant that very essential portion of every plant which 
 remains behind, after the action on the vegetable 
 tissue of various solvents, such as water, dilute acid 
 and alkali, alcohol and ether, successively applied, 
 by which sugar, gum, resin, colouring matter, &c., are 
 each in turn removed, and nothing is left but a kind 
 of white fibrous skeleton, insoluble in all those media. 
 Fine linen or cambric will give a very good idea of 
 the lignin of the chemist. 
 
 When examined by a good microscope, the ulti- 
 mate fibres of lignin present the appearance of mi- 
 nute flat ribands, with rolled or thickened edges. 
 These are no doubt distinctly organized, and very 
 complex in chemical constitution. 
 
 Lignin may be converted into sugar by artificial 
 means, passing like starch through an intermediate 
 state, resembling dextrine. 
 
 GUM. This is another very abundant vegetable 
 product. Gum-arabic, from an acacia, and the gum 
 of the cherry and plum-tree, are familiar to every 
 one. Gum often exudes from wounds in the bark ; 
 and it is doubtful whether it is not, in some measure, 
 a product of disease. This substance is one of great 
 importance in many of the useful arts, being employ- 
 ed in large quantities ; it never crystallizes, and is 
 
VEGETABLE CHEMISTRY. 67 
 
 easily distinguished, by its peculiar chemical charac- 
 ters, from the other vegetable principles. Many 
 varieties, obtained from different trees, exist. 
 
 Such are the principal members of the very im- 
 portant class of neutral, non-azotized, vegetable 
 principles. Several other substances, of less interest, 
 belong to the same division, and have been passed 
 over without notice ; it remains to describe the chemi- 
 cal nature of these bodies. They are, as already 
 stated, ternary compounds of carbon, hydrogen, and 
 oxygen ; with this very remarkable feature, that the 
 two latter elements are present invariably, with per- 
 haps one exception in the proportions to form water. 
 This ratio of the oxygen and hydrogen may be taken 
 as one great distinctive character of the group ; it is 
 found elsewhere, it is true, but only in a very few 
 bodies such as lactic and acetic acids derived im- 
 mediately or remotely from some one or other of the 
 series. Another good character is that of neutrality 
 disinclination to form chemical compounds with 
 other substances ; they do, however, occasionally 
 combine in a definite manner, but with a degree of 
 energy very far feebler than that observed in the case 
 of many other organic principles. Thus sugar and 
 starch unite with lime and oxide of lead : starch 
 with iodine, forming a well-known blue compound 
 of great beauty of tint ; and many other cases might 
 be mentioned, so that the term " neutral " must be 
 understood comparatively. 
 
 The VEGETABLE ACIDS claim a moment's attention. 
 These occur, often in large quantities, throughout 
 the whole vegetable kingdom ; they are generated 
 
68 VEGETABLE CHEMISTRY. 
 
 in the plant for purposes yet, for the most part, un- 
 known, and afterwards often become highly valuable 
 to mankind in their applications to medicine and the 
 useful arts. It is not unlikely, also, that a beneficial 
 effect may be produced by these bodies upon the ani- 
 mals to which the plants serve for food. 
 
 The vegetable acids seldom occur in a free state, 
 the most usual condition is in that of a salt of an 
 alkali, or earth, or sometimes an organic alkaline 
 principle ; a salt of potash, with excess of acid, is 
 very common. When a vegetable substance is 
 burned, these organic acids are destroyed, and the 
 bases, for the most part, converted into carbonates ; 
 hence the alkalinity of ordinary wood-ashes from 
 carbonate of potash a substance, in practice, en- 
 tirely derived from this source, although, as before 
 shown, this alkali is an original and essential con- 
 stituent of the unorganized earth; it is collected by 
 plants from the soil, and accumulated in their sub- 
 stance in an easily available form for the use of man. 
 If it were necessary, in order to procure potash, to 
 extract it from the earth itself, the trouble and cost 
 of the process would be so great as almost to pro- 
 hibit its use. 
 
 With respect to chemical composition, the vege- 
 table acids usually exhibit a larger comparative quan- 
 tity of oxygen than the other proximate principles ; 
 the most common of them the tartaric, citric, and 
 malic are examples. They are destitute of azote. 
 
 FATTY SUBSTANCES FIXED AND VOLATILE OILS. 
 The oils and fats form an important series of bodies, 
 characterized, in a chemical point of view, by a de- 
 
VEGETABLE CHEMISTRY. 69 
 
 ficiency of oxygen, sometimes amounting to a total 
 absence of that element ; their highly combustible 
 nature is connected with this peculiarity. Fatty 
 matters, in some shape, although never entirely ab- 
 sent from vegetables, are only in some particular 
 instances to be noticed in large quantity. Seeds are 
 very often loaded with oil, or soft fat, which may be 
 extracted from them by simple pressure, or by heat- 
 ing with water. All the vegetable oils of commerce 
 are got in this way, with the exception of olive oil, 
 which comes from the fruit. 
 
 The fixed vegetable oleaginous principles bear 
 the strictest resemblance, in every respect, to the ani- 
 mal fats. They have, when pure, very little taste or 
 smell ; they cannot be converted into vapour without 
 decomposition, and undergo, like the corresponding 
 animal principles, a change, when heated with caus- 
 tic alkalies, in which the fat is resolved into two new 
 bodies, namely, a fatty substance, having decided 
 acid properties, and a kind of uncrystallizable sugar, 
 called glycerine. These reactions have been made 
 the subject of much admirable research, but the 
 question is too purely chemical for the present essay ; 
 it is practically important, however, because it is by 
 such a change that we get the very valuable article, 
 soap. 
 
 The volatile oils are in general remarkable for 
 their powerful odours often very agreeable, some- 
 times otherwise. They are further distinguished by 
 the facility with which they evaporate ; a drop upon 
 paper soon passes off, and leaves no stain. The odours 
 of flowers and of certain woods are due to these 
 
70 VEGETABLE CHEMISTRY. 
 
 principles. The study of the volatile oils forms a 
 very interesting branch of organic chemistry ; and it 
 is satisfactory to find that something has already been 
 done towards elucidating the origin of these in 
 the plant, and showing their connexion with the 
 other proximate principles.* Volatile oils are often 
 of great economical use : the oil of turpentine, for 
 instance, in the manufacture of varnish, and other 
 applications. 
 
 Closely connected with the above are the RESINS, 
 of which we have numerous varieties. These are 
 looked upon as oxidized volatile oils f and, in fact, it 
 has long been known that the last-named substances, 
 by long exposure to air, absorb oxygen, and assume 
 the aspect of resin. The resins are insoluble in 
 water, fusible, burn readily, and cannot be volatilized ; 
 they often possess acid properties, and form salts with 
 metallic oxides. 
 
 We have now to consider the vegetable princi- 
 ples containing nitrogen ; and these we subdivide 
 into two sections 1st, the VEGETO-ALKALIS ; and, 
 2nd, the ALBUMINOUS PRINCIPLES. 
 
 In a systematic work on chemistry, it would be 
 indispensable to devote a considerable space to the 
 vegeto-alkalis ; they occur here and there in a few 
 plants, always in very small quantities, but then 
 their peculiarities of constitution, and extraordinary 
 
 * Allusion is more particularly meant to the researches of 
 Piria and Dr. Ettling on salicin and the products of its oxy- 
 dation ; those of Cahours and Dumas, on potato-oil and vale- 
 rianic acid, &c. 
 
VEGETABLE CHEMISTRY. 71 
 
 powers over the animal system, claim for them, with 
 justice, a prominent place. These bodies are dan- 
 gerous weapons intrusted to our care ; they may be 
 used for good or for evil ; as a fearful poison or as a 
 valuable medicament, according to the hands they 
 fall into. And it is, to all appearance, not without 
 special design, that nature has been so sparing in 
 the production of such substances, and has so envel- 
 oped with difficulties their isolation, that the know- 
 ledge and possession of them are of necessity con- 
 fided to few, and to those least likely to make a bad 
 use of them. With respect to these, a very few 
 words will suffice. The vegeto-alkalis are, for the 
 most part, colourless, crystallizable substances, nearly 
 insoluble in water, but dissolving in spirit, having an 
 alkaline reaction to test-paper, and forming distinct 
 and definite salts with the ordinary acids. They 
 contain a tolerably large proportion of nitrogen, and 
 are very little subject to spontaneous change. 
 
 Far more interesting bodies are the albuminous 
 principles ; it is only very lately that the full im- 
 portance of these, in connexion with animal exist- 
 ence, has been made manifest. The recent invalu- 
 able investigations of Professor Liebig have put these 
 substances in a very different position from that they 
 formerly occupied in the estimation of chemists and 
 physiologists. To discuss these matters fully, how- 
 ever, at present, would involve a too extensive an- 
 ticipation of the subject of animal chemistry ; let it 
 suffice, therefore, to remark respecting one or two of 
 the lower and more subordinate offices, if the term 
 
72 VEGETABLE CHEMISTRY. 
 
 may be permitted, which these substances fill in the 
 general economy of nature. 
 
 The change by which sugar becomes converted 
 into spirit is brought about, in all cases, by the agen- 
 cy of one or other of these principles. < It has been 
 shown that the conditions under which vinous fer- 
 mentation takes place always involve the necessity 
 of the presence of azotized organic matter of this 
 peculiar kind, in the absence of which the most fa- 
 vourable circumstances of temperature, access of air, 
 and degree of dilution, fail to excite in a saccharine 
 liquid the alteration spoken of. 
 
 When a sweet vegetable juice, like that of the 
 grape or the sugar-cane, is exposed to the air, at a 
 temperature of 60 or 70 F., it is observed, after a 
 few hours, to become turbid and muddy, while, at the 
 same time, minute bubbles of gas are seen to arise 
 from all parts of the liquid, and ascend to the surface, 
 entangling, in their upward progress, a quantity of 
 the insoluble matter just alluded to, and giving rise 
 to a scum or froth. This simultaneous disengage- 
 ment of gaseous matter, and production of insoluble, 
 dirty white, flocky precipitate, from the clear vege- 
 table juice, go on rapidly increasing for a certain 
 length of lime, depending very much upon the 
 warmth of the sur jnding air. After a while the 
 action slackens, and eventually ceases ; the greater 
 part of the insoluble matter collects at the bottom of 
 the vessel, a little remains at the top, whije the great 
 mass of the liquor once more becomes clear. If a 
 portion be now drawn off from the sediment and ex- 
 
VEGETABLE CHEMISTRY. 73 
 
 amined, it will be found to have lost, in a great 
 measure, its sweet taste, and tohaveacquired^anoth- 
 er quite distinct ; it has also become intoxicating, 
 and capable of furnishing, by distillation or other- 
 wise, a colourless, inflammable liquid, easily recog- 
 nized as alcohol. The gas evolved during this fer- 
 mentation is carbonic acid in a state of considerable 
 purity. 
 
 This is an example of the change called " vinous 
 fermentation" a change to which all saccharine 
 liquids are subject, provided they contain in solution 
 azotized matter capable of putrefying, and are placed 
 in circumstances favourable to that event. The 
 azotized principle runs into spontaneous decay ; it 
 is slowly resolved into carbonic acid, ammonia, and 
 other products, and the molecular disturbance thus 
 produced in the decomposing body, or "ferment," 
 is propagated to the sugar, the equilibrium of oppos- 
 ing attractions among the three elements of that sub- 
 stance is overthrown, while new and more stable 
 compounds arise in place of that destroyed. 
 
 Conversion into alcohol is by no means the 
 only change which sugar is susceptible of under- 
 going under the strange influence of a ferment, or 
 decomposing azotized body. It may pass into an 
 acid state, and give rise to one of the most curious 
 organic acids existing, the lactic; or, lastly, it may 
 be converted, partially, at least, into the sweet prin- 
 ciple of manna, a substance which departs somewhat, 
 as already hinted, from the sugar series. The kind 
 of change induced, appears to depend altogether on 
 the particular stage of decomposition of the ferment 
 4 
 
74 VEGETABLE CHEMISTRY. 
 
 itself, whose powers thus vary with the progress of 
 its own decay. 
 
 These phenomena attract at the present moment 
 a large share of attention, and they well deserve it ; 
 if the mysteries of vital chemistry are fated to be in 
 any degree unravelled, it will probably be by the 
 careful investigation of reactions such as these, 
 which the ordinary laws of the science fail to ex- 
 plain. For the moment, it may be remarked, that 
 nothing can place in a clearer light the very singu- 
 lar properties of these organic compounds proper- 
 ties which, be it remembered, they owe to those of 
 their truly Protean elements, carbon, hydrogen, oxy- 
 gen, and nitrogen. 
 
 The decay of organic tissues, the bodies of plants 
 and animals, is a process which has for its object 
 not only the removal of useless matter, but its con- 
 version into a form once more capable of supporting 
 life. We shall discern, as we proceed, that repro- 
 duction and decay follow each other's footsteps 
 throughout the whole system of Nature, and that the 
 conditions of life and death are mutually involved in, 
 and dependent upon, each other. 
 
 The great agent in all these actions is the free 
 oxygen of the air, and the ultimate result is the 
 transformation of the organic substance into such 
 bodies as carbonic acid, water, carburetted hydro- 
 gen, ammonia, or nitric acid. The intermediate 
 states, however, passed through, are very numerous 
 and very imperfectly understood ; still, there is 
 every reason to think that they resemble those through 
 which sugar passes, in the example before given, in 
 
VEGETABLE CHEMISTRY. 75 
 
 descending by a regular gradation of simplicity of 
 form. 
 
 The constant, never-ceasing activity of free oxy- 
 gen, is thus not only the mainspring, the motive- 
 power, of life, in both animal and vegetable king- 
 doms, but it is the cleanser, the purifier, of earth and 
 air and sea, from the defilements constantly poured 
 upon, and into these latter, from the countless 
 sources of poisonous contamination around us. Va- 
 pours of volatile substances, rich in hydrogen, the 
 putrid effluvia of pestilence, become gradually de- 
 stroyed by a real process of burning, more slowly, 
 but not less completely, than in the flame of a 
 furnace. The water of lakes and rivers, and of 
 the great ocean itself, owes its sweetness to the 
 same cause ; the gas is dissolved, and penetrates to 
 every part, quietly destroying in its progress every 
 thing offensive. This is the explanation of the 
 spontaneous purification which accumulations of 
 foul water, freely exposed to the air, are well known 
 to undergo ; the impurities suffer oxidation, partly 
 becoming destroyed, that is, converted into inorgan- 
 ic products, partly rendered quite insoluble, and so 
 separated mechanically. These, however, in the 
 end, disappear from continuance of the same cause, 
 and suffer a similar fate. 
 
 It will be unnecessary to insist upon the obvious 
 fact that these arrangements are not merely condu- 
 cive to the welfare and comfort of all living crea- 
 tures, but to their very existence. 
 
 Mult plants live upon the air ; they get their 
 
76 VEGETABLE CHEMISTRY. 
 
 carbon from its carbonic acid, their hydrogen from 
 its moisture, and their nitrogen from the little am- 
 moniacal vapour which there exists. Plants thus 
 feed upon inorganic substances, and the proof is not 
 very difficult to give. 
 
 The simple fact of the decomposition of car- 
 bonic acid by green and living plants exposed to 
 the light, is as old as the time of Dr. Priestley. 
 Subsequent experimenters have shown that this 
 effect takes place with equal facility, whether the 
 gas be dissolved in water, and the plant immersed in 
 the solution, or merely diffused through a quantity 
 of atmospheric air in contact with its leaves : in 
 both cases, the carbonic acid gradually disappears, 
 and is replaced by free oxygen. 
 
 There are two conditions indispensable to the 
 success of .this experiment namely, a sound and 
 healthy condition of the leaf itself, and the pres- 
 ence of light. It is not necessary to have the di- 
 rect solar beam ; diffuse daylight is sufficient, al- 
 though the action is not, in this case, so rapid and 
 energetic as when aided by the bright rays of the 
 sun. 
 
 In the absence of light these effects are exactly 
 reversed j oxygen is withdrawn from the air and 
 carbonic acid emitted, so that plants in the dark 
 deteriorate the air in which they are confined. 
 
 The ultimate effect of living vegetables upon the 
 atmosphere was for a long time a question among 
 philosophers ; it appeared doubtful to the minds of 
 many, whether, in the case of an ordinary plant 
 a tree, for example, exposed under the open heaven to 
 
VEGETABLE CHEMISTRY. 77 
 
 the alternations of light and darkness, sunshine and 
 gloom the oxygen disengaged during the day, 
 more than compensated the carbonic acid emitted in 
 the night ; whether, upon the whole, the effect of 
 vegetation might not be null, or even hurtful, as re- 
 gards the withdrawal of mephitic gas from the at- 
 mosphere, instead of being beneficial in the highest 
 degree, as some supposed. 
 
 This question has now, to all appearance, been 
 completely set at rest ; experiments conducted in 
 the most unexceptionable manner have fully shown, 
 that a green, leafy plant, in full health and vigour, 
 enclosed within an air-tight glass vessel, and fre- 
 quently supplied with small quantities of carbonic 
 acid during the space of many days, possesses the 
 power of absorbing and decomposing that gas to 
 such an extent, that the proportion of oxygen in the 
 artificial atmosphere in which the plant is immersed 
 may rise nearly ten per cent, above the normal 
 quantity. It must be remembered, too, that in re- 
 searches of this kind, plants are, of necessity, placed 
 in somewhat unusual and disadvantageous circum- 
 stances, so that their powers are limited and crippled, 
 and not to be compared to those they enjoy in their 
 natural condition : they lose health, shrivel, and die, 
 and then commences a putrefactive decomposition, 
 the result of which is, invariably, the production of 
 carbonic acid. It is to the neglect of this fact that 
 the failures and discrepancies in the earlier experi- 
 ments are due. 
 
 It is not easy to account for the uniform disen- 
 gagement of carbonic acid in the absence of the 
 
78 VEGETABLE CHEMISTRY. 
 
 light-stimulus : it may be that the plant really re- 
 spires, consuming oxygen, and generating carbonic 
 acid like an animal, but to a far smaller extent. It may 
 be, on the contrary, merely a consequence of a chem- 
 ical change, an act of oxidation of the moist vegeta- 
 ble matter exposed to the air. There are arguments 
 which might be adduced in favour of both these 
 views; it is a point, however, the discussion of which 
 may be, in the present instance, safely neglected, 
 inasmuch as its decision, one way or the other, will 
 not affect the general question of the influence of 
 vegetables on the air. 
 
 So far all is satisfactory; we have the full- 
 est reason to believe that plants are nourished by the 
 carbonic acid of the atmosphere, which is absorbed 
 directly by their leaves from the surroundin^fair, and 
 also by their roots, when dissolved by rain-water ; 
 and, further, that the rapidity of this decomposition 
 bears a direct relation to the intensity of the light. 
 
 In the tropics, for example, vegetation is wonder- 
 fully active, and this is due as much to the brighter 
 sunshine, as to the more elevated temperature of 
 these parts. There is no difficulty in obtaining in a 
 stove or conservatory, an atmosphere as warm, and, 
 if necessary, as moist as may be desired, and the 
 plants of hot countries may be cultivated with a 
 certain deg/ee of success in such a situation, but they 
 never exhibit the thriving and beautiful appear- 
 ance, the deep green colour, characteristic of health, 
 belonging to them in their natural state. We may 
 substitute artificial warmth for that of the sun, but 
 we cannot supply the place of its light. 
 
VEGETABLE CHEMISTRY. 79 
 
 The most valuable proof, however, of the prin- 
 ciple laid down, is to be found in the observation of 
 the manner in which forest trees are sustained and 
 fed. It is easy to show that, instead of the earth in 
 which they stand becoming exhausted of its carbon 
 to supply their wants, it actually becomes enriched 
 in that substance. The carbonaceous matter of the 
 soil, the "humus" of the agricultural writers, is in 
 fact nothing more than decaying vegetable matter 
 which once had life; its quantity increases year by 
 year, provided the ground be not disturbed and laid 
 open to the oxidizing power of the air. We cannot 
 attribute to this the office of supplying carbon to the 
 trees ; and except the carbonic acid of the air, there 
 is no other source from whence it could be derived ; 
 so that, if positive experimental evidence on the sub- 
 ject did not exist, we should still be driven to the 
 same conclusion. 
 
 In the case of cultivated plants, where the soil is 
 constantly loosened by ploughing or digging, the 
 humus may become useful as a source of carbonic 
 acid by its decay, while the manure put upon the 
 land is efficient, not so much on account of the car- 
 bon it contains, as of the nitrogen in the shape of 
 ammonia, or of putrescible matter capable of becom- 
 ing ammonia. Pure humus, decomposed woody 
 fibre, is worth next to nothing, as those well know 
 who have made the experiment. 
 
 If plants decompose carbonic acid, still more 
 easily may we admit their power of decomposing 
 water. This faculty is exerted in the production of 
 each and every one of the proximate principles 
 
80 VEGETABLE CHEMISTRY. 
 
 which make up their solid frame. All these involve 
 the separation of the elements of water as well as- 
 of those of carbonic acid. Even when oxygen and 
 hydrogen exist in the ratio of the equivalents, it is- 
 accessary to suppose that this must occur. When 
 resinous and oily pringiples, containing a large ex- 
 cess of hydrogen, are concerned, the case is still 
 clearer. 
 
 Then for the nitrogen : although it cannot at 
 present be positively proved that plants never absorb 
 and fix the free nitrogen of the atmosphere, yet it 
 can be rendered highly probable that they are desti- 
 tute of this faculty. In the first place, the supposi- 
 tion is not necessary, from the occurrence of ammonia 
 in the air, little as it is ; and, in the second, the ob- 
 servation of the effects of ammoniacal compounds 
 on vegetation gives the most convincing evidence of 
 the value of ammonia in this respect. The azotized 
 constituents of plants, more especially of wild plants, 
 always bear but a very small proportion to those 
 destitute of nitrogen, and for their production the 
 natural supply of ammonia from the air is no doubt 
 sufficient ; but when we come to cultivate them, and 
 to develop to an abnormal extent the parts of the 
 system containing these azotized matters, the supply 
 becomes insufficient, and we are accustomed to make 
 up the deficiency by manure. 
 
 Allusion has already been made to the saline^ 
 inorganic matters of plants. These are, of course, 
 supplied by the soil, which is thus often subject to- 
 exhaustion, unless means are taken to remedy the 
 defect It is difficult to explain the use of thes 
 
VEGETABLE CHEMISTRY. 81 
 
 substances to the plant ; but the regular and invari- 
 able manner in which they occur, and the sterility 
 occasioned by their absence from the ground, concur 
 in bearing testimony to their importance. 
 
 If we cannot exactly tell the use of these things 
 to the plant itself, and feel difficulty in assigning a 
 reason for the care with which they have been pro- 
 vided, and at the same time made indispensable, 
 that difficulty vanishes at once when we take into 
 consideration the end the plant itself has been des- 
 tined to fulfil. The bones or shells of the animals 
 they nourish are constructed in great part of inor- 
 ganic matter. The circulating fluids contain abun- 
 dance of soluble salts, which perform important 
 functions in the body. These must be provided in 
 proper quantity, and of the right kind, or the crea- 
 ture becomes diseased and dies. The earthy phos- 
 phates are as much wanted as the substance from 
 which flesh is formed. 
 
 There is a curious class of vegetables, the phy- 
 siology of which is at present but little understood, 
 the fungi. These appear to differ altogether in 
 many points from the green plants ; their power of 
 decomposing carbonic acid is denied ; they are stated 
 to vitiate the air instead of purifying it ; light is not 
 essential to them, and they thrive in circumstances 
 of the most extraordinary kind. It is very possible 
 that these beings may be constituted in a manner 
 altogether different from ordinary plants ; may feed 
 on organic matter, like animals. They are, indeed, 
 the scavengers of the vegetable kingdom, commis- 
 4* 
 
82 VEGETABLE CHEMISTRY. 
 
 sioned to assist in the destruction and removal of once 
 living but now lifeless forms. 
 
 These are some of the most prominent facts 
 which a rapid survey of the vegetable world makes 
 evident to us, but there are many other things which 
 might be mentioned as giving proofs of design and 
 adaptation of the most general and comprehensive 
 character. To take a single one. Next to his food, 
 man's most pressing want, even in the rudest state 
 of society, is protection against cold. He employs 
 fire for the purpose ; that is to say, he takes means 
 for developing violent chemical action between 
 the elements of certain combustible substances and 
 the oxygen of the air, and of availing himself of 
 the heat thence disengaged. But does one man in 
 a thousand, while enjoying the warmth of his fire, 
 reflect for a single moment on the combination of 
 circumstances to which his pleasure is due ? Does 
 he reflect on the very peculiar nature of the fuel pro- 
 vided for him in the forest and the field, or in the black 
 bituminous coal, the relic of a vegetation now pass- 
 ed away ? Does he pause for a moment to consider 
 that the characteristic components of his blazing 
 log, the carbon and the hydrogen, are the only ele- 
 mentary substances in existence fitted for the pur- 
 pose ; the only bodies whose products of combus- 
 tion are of such a kind as to pass off in invisible and 
 odourless form, to mingle in the air, and eventually 
 to return again into the very same condition as that 
 which has just been destroyed ? It is most wonder- 
 ful, when we reflect on these things/ to observe 
 
VEGETABLE CHEMISTRY. 83 
 
 how much our physical happiness depends upon 
 what some will call accidental circumstances. Is it 
 by accident that carbonic acid is oddtrless, and 
 harmless also, unless in considerable quantity, while 
 the oxides of all other combustible substances, capa- 
 ble of existing in a gaseous state, are pungent and 
 irritating, and insufferable in the smallest doses'? A 
 few hundred cubic inches of carbonic acid escaping 
 into an apartment of small dimensions, so far from 
 occasioning inconvenience, would be absolutely in- 
 appreciable. A thousandth part of that quantity of 
 sulphurous acid would render the air irrespirable. 
 
 The greater number of combustible substances 
 have fixed and solid oxides. What, it may be asked, 
 would be the consequence if we had to burn phos- 
 phorus or zinc for fuel ? Where would be our 
 fireside comforts? still more, where our manufac- 
 tures ? How should we reduce iron from the ore, or 
 make porcelain or glass, or, in fact, perform anyone 
 of the thousand operations for which high heat may 
 be required? For the purposes of artificial light, 
 too, we have once more to trust to carbon and hydro- 
 gen. It would be difficult to find any thing else 
 that would answer the purpose so well, at any rate. 
 It is, in truth, among the common, every-day con- 
 cerns of life that we find the most remarkable adap- 
 tations of all external nature to our wants. The 
 philosopher may produce cases which arouse and 
 startle by their novelty, but they can hardly surpass 
 those that lie upon the very surface, open to the ob- 
 servation of all, and only to be neglected from the 
 familiarity of unreflective enjoyment. 
 
ANIMAL CHEMISTRY, 
 
 IN order to convey to the mind of the reader a 
 proper idea of the fundamental facts and doctrines 
 of Animal Chemistry, and of the manner in which 
 these bear upon the argument of design, it will be 
 necessary to enter more into detail than the author 
 has ventured to do in the preceding part of the 
 essay. 
 
 The animal body is made up of certain solids 
 and fluids in very unequal proportions. The solids 
 determine the general figure and magnitude of the 
 whole structure ; the fluids communicate the round- 
 ed contour, softness, and pliancy, so essential to the 
 well-being of the system. They are obviously mere 
 watery solutions of various organic and inorgan'c 
 substances, of which mention will be made almost 
 immediately, and with them the solids are more or 
 less distended and swollen, as their texture permits. 
 By slow desiccation, this water may be got rid of, 
 and the body sometimes reduced to less than a tenth 
 of its original weight, or to little more than that of 
 its bony skeleton. The mummies of Egypt and the 
 New World are examples of this complete drying. 
 
 It will be proper to study, in succession, the 
 chemical history of the chief compounds of the body ; 
 
ANIMAL CHEMISTRY. 85 
 
 of the blood, from which the body itself is built up ; 
 and, lastly, the nature of food and its functions. It 
 must be premised, that the observations about to be 
 made are to be understood as applying in their great- 
 est force to the higher classes of animals, and espe- 
 cially to man; our knowledge of vital chemistry is, 
 at present, almost entirely confined to these. 
 
 Among the proximate animal constituents there 
 is a small group of three substances, related in a 
 very close and intimate manner among themselves, 
 and having properties in the highest degree remark- 
 able and worthy of attentive study. These are 
 albumen, fibrin, and casein. The two first-named 
 are diffused through the whole body ; the third is 
 found only in a special secretion. We may call 
 them, for the sake of simplicity, the albuminous 
 principles. 
 
 White of egg, or the clear " serum," or fluid 
 part of the blood, may be taken as an example of 
 albumen, as found in the body; perhaps the only 
 condition in which it is ever so found. In this con- 
 dition it presents the aspect of a glairy, adhesive li- 
 quid, of pale yellow colour and slightly saline taste, 
 due to a quantity of common salt and chloride of po- 
 tassium held by it in solution. If a piece of delicate 
 reddened litmus paper be plunged into this liquid al- 
 bumen, from whatever source derived, a blue tinge 
 is immediately produced, indicative of the presence 
 of an alkali. Further, it is in this state miscible 
 with water in all proportions, and dries up, if spread 
 ipon a plate in a warm room, to a brittle, yellow, 
 
85 ANIMAL CHEMISTRY. 
 
 gum-like mass, which, when put into warm water, 
 swells, softens, and finally dissolves. 
 
 The alkaline condition of soluble albumen is es- 
 pecially deserving of notice. It is, in fact, to this 
 free soda for to such is the effect due that the 
 albumen itself owes its solubility; for if acetic acid 
 be added, drop by drop, to serum, or diluted white of 
 egg, until the alkaline reaction disappears, and then 
 the whole suddenly mixed with a large quantity of 
 pure cold water, the albumen is observed to separate 
 in flocks, which, after a little repose, collect at the 
 bottom of the vessel in which the experiment is made. 
 These flocks are, in reality, pure albumen, which is 
 thus seen to be insoluble in water when freed from 
 the alkali with which it is always naturally associ- 
 ated. A very small quantity of potash or soda re- 
 dissolves it, and the solution once more exhibits its 
 usual characters. 
 
 Every one is, of course, familiar with the very 
 curious change which white of egg undergoes on the 
 application of heat a change common to all liquids 
 containing ordinary soluble albumen. The obvious 
 alteration is a passage from the soluble to the insol- 
 uble state, or what is called "coagulation." No 
 contrast can be greater than that between boiled and 
 unboiled white of egg. Their chemical properties 
 are also essentially different, and yet the chemist can 
 detect no change of composition in the substance. It 
 is true that the water extracts a little alkali and a 
 trace of sulphuret of sodium, but the abstraction of 
 these bodies is hardly sufficient to account for the 
 change in question. 
 
ANIMAL CHEMISTRY. 87 
 
 So far, therefore, as appearances at present go, 
 the proximate animal principle, albumen, possesses 
 the property of existing in two separate states with- 
 out change of chemical composition ; and, further, 
 the passage from the one to the other is effected by 
 the mere agency of heat, the application of a tem- 
 perature which need never exceed that of boiling 
 water. This is the great characteristic property of 
 albumen, by the aid of which it is distinguished from 
 all other substances. 
 
 The second body of the group, fibrin, is found in 
 two distinct conditions in the living animal ; in the 
 blood, namely, where it is dissolved, perfectly fluid, 
 and in the muscular flesh, of which it forms the cha- 
 racteristic ingredient. It is here solid and insoluble, 
 or coagulated. 
 
 When a thin slice of muscle is washed in cold 
 water until perfectly white, it is seen to consist of a 
 stringy-looking substance, which is the fibrin itself, 
 traversed in all directions by blood-vessels, and 
 nerves, and membranous matter. It may be ex- 
 tracted from blood in a much purer condition by 
 strongly agitating that fluid, in its recent and yet 
 warm state, with a bundle of twigs; the fibrin attaches 
 itself to the extremities of these latter in the shape of 
 long elastic strings, which by patient washing may 
 be entirely freed from colour. It is not, however, 
 yet pure, inasmuch as it still contains fat in consid- 
 erable quantity. By drying, it shrinks prodigiously 
 in volume, becomes transparent and horny, and in 
 that state may be preserved indefinitely. 
 
 The experiment just described serves to exhibit, in 
 
88 ANIMAL CHEMISTRY. 
 
 a very characteristic manner, the chief peculiarity of 
 the substance under discussion ; its capability of as- 
 suming the solid form spontaneously, so soon as it is 
 withdrawn from the influence of life. Owing to this 
 circumstance, little or nothing is known of the other 
 properties of fibrin in the soluble state; all the ex- 
 periments of chemists have of necessity been made 
 upon that which has undergone coagulation. 
 
 The third substance, casein, is found only in milk, 
 where it exists in a state of perfect solution, owing, 
 like albumen, its solubility to a small quantity of al- 
 kali. Unlike the substance just mentioned, how- 
 ever, casein is not coagulated by heat ; milk may. as 
 is well known, be boiled without any change of the 
 kind. The addition of a little acid, of almost any 
 description, determines the precipitation of the casein 
 by withdrawing the alkali which held it in solution ; 
 and it is interesting to observe the very small amount 
 of acid required for this purpose when the reaction 
 is aided by a gentle heat. 
 
 The manufacture of cheese depends upon this 
 property of casein, which appears to have been, 
 until quite recently, much misunderstood. When 
 a piece of the lining membrane of the stomach of 
 an animal, more particularly of a young animal, as 
 a calf, is cleansed by slight washing in cold 'water, 
 plunged into a large mass of milk, and then the 
 temperature of the whole slowly raised to about 
 120 or a little higher, it is observed that, at a 
 particular moment, the milk undergoes coagula- 
 tion of a very complete kind ; it separates into solid, 
 white, opaque " curd," and thin, pale-coloured, 
 
ANIMAL CHEMISTRY. 89 
 
 translucent " whey ;" the former consisting chiefly 
 of casein and butter, and the latter of water, holding 
 in solution most of the saline components of the 
 milk, together with the substance to which it owes 
 its sweetness; this is the " milk-sugar" of chemical 
 writers ; a body to which reference will again be 
 made. For the purpose of preparing cheese, the 
 coagulum so produced is drained, mixed with salt, 
 and sometimes other condiments, and after various 
 manipulations, the principal object of which is to 
 communicate consistence and form, and get rid of 
 superfluous moisture, the cheese is suffered to remain 
 several months in a cool situation, where it under- 
 goes that particular kind of putrefactive change 
 upon which its flavour and value depend. 
 
 The coagulation of milk, under the influence of 
 a simple wet membrane, is a phenomenon so remark- 
 able, and so difficult to explain, that we need not 
 wonder at the attention it has excited. Experi- 
 ments have been made with a view of ascertaining 
 the effect on the membrane itself. Among these, 
 a very curious one is due to Berzelius : he relates 
 that he took a bit of the lining of a calf's stomach, 
 washed it clean, dried it as completely as possible, 
 weighed it carefully, put it into eighteen hundred 
 times its weight of milk, and heated the whole to 
 120 F. After some little time, coagulation was 
 complete. He then removed the membrane, washed, 
 dried, and once more weighed it; the loss amounted 
 to rather more than ^ of the whole. According to 
 this experiment, one part of the active matter dis- 
 
90 ANIMAL CHEMISTRY. 
 
 solved from the membrane had coagulated about 
 thirty thousand of milk. 
 
 The researches of several French philosophers 
 on the lactic acid fermentation, and the still more 
 recent experiments from the Giessen laboratory, on 
 the condition of casein in milk, permit a tolerably 
 satisfactory explanation of this singular change, by 
 linking it to a multitude of others, in which a com- 
 mon principle is involved. It has been shown that 
 the si:gar of milk, a substance differing very con- 
 siderably in properties from both cane and grape 
 sugar, is peculiarly prone, under favourable cir- 
 cumstances, to pass into lactic acid by appropriat- 
 ing the elements of water.* The presence of a 
 ferment, or decomposing azotized body, is essential 
 to this change, as to all of like nature, but the 
 origin of the ferment itself is a matter of perfect 
 indifference; it may come from either the vegetable 
 or the animal kingdom ; it matters not, provided only 
 that it be in the proper stage of decay for developing 
 the lactic acid fermentation. Now it appears that an 
 animal membrane such as that adverted to, removed 
 from the body and left a short time in contact with 
 water, is in reality very frequently in this particular 
 condition. Decay commences the moment life is ex- 
 tinct, long before any thing like putrescence is percep- 
 tible, and the result of this decay, insensible to all ordi- 
 nary means of observation, is the acquisition by the 
 decomposing body of the power of becoming a lactic 
 acid ferment. A piece of " rennet " is put into a 
 
 * See Appendix, No. 2. 
 
ANIMAL CHEMISTRY. 91 
 
 quantity of fresh milk ; it immediately begins to exert 
 its fermentive power upon the milk-sugar present. 
 In the course of a very short time, enough lactic 
 acid is formed under its influence to saturate the 
 alkali which holds the casein in solution, whereupon 
 the base is, by the aid of a little heat, entirely with- 
 drawn by the acid from the casein, and the latter 
 rendered in consequence insoluble. 
 
 The quantity of lactic acid really required for 
 bringing about this decomposition is extremely mi- 
 nute ' } a mere trace is enough. The casein itself, 
 too, may, if a little time be allowed, act the part of 
 ferment to the sugar, and give rise to lactic acid. 
 There is no lactic acid in pure, fresh milk ; after a 
 few hours it makes its appearance, however, and 
 continues to increase in quantity until enough has 
 been generated to coagulate the casein, even in the 
 cold, and to communicate to the whole a powerfully 
 acid re-action. Casein, then, is sufficiently charac- 
 terized by being precipitated from its solution by 
 feeble acids which do not coagulate albumen, and 
 by not being coagulable by the aid of heat. 
 
 The chemical composition of these three bodies 
 albumen, fibrin, and casein has been made the 
 subject of many careful inquiries. It is only within 
 the last few years that the practical analysis of or- 
 ganic substances has been in a state of sufficient 
 advancement to be applicable to investigations of 
 such a difficult and delicate nature as those which 
 have for their object the determination of the exact 
 proportions in which the elements of bodies of this 
 kind are associated. Step by step, however, ana- 
 
92 ANIMAL CHEMISTRY. 
 
 lytical processes have been improved, both in accu- 
 racy and ease of execution, until very little has been 
 left to desire on this point. 
 
 M. Mulder, of Amsterdam, has the distinguished 
 honour of having made the first correct and consistent 
 analysis of a great number of complex animal prin- 
 ciples, including those described ; the difficulties he 
 had to encounter in this task were very great, and 
 the manner in which they were surmounted reflects 
 the highest credit on his sagacity and skill. Many 
 of the results of Mulder's researches have' been con- 
 firmed by the subsequent experiments of Scherer, 
 Dr. Bence Jones, and others. 
 
 It appears that albumen arid fibrin are com- 
 pounds of carbon, hydrogen, nitrogen, oxygen, sul- 
 phur, and phosphorus ; casein contains, it is said, 
 but five elements, phosphorus being absent. The 
 most remarkable feature of the case, however, is the 
 absolute identity of composition of these three bodies 
 as respects the carbon, hydrogen, oxygen, and nitro- 
 gen; the only difference is to be found in the sulphur 
 and phosphorus, which bear, it must be remarked, 
 an exceeding small proportion to the other con- 
 stituents. 
 
 The extreme importance of this discovery will 
 probably be apparent in some measure even now. 
 It will explain, in the simplest and most beautiful 
 way conceivable, the fact which we know to occur 
 of the constant transmutation in the animal system of 
 one of these substances into the other ; it will show 
 ho\v easily the milk of the mother becomes the flesh 
 of the offspring, and with what simple change the 
 
ANIMAL CHEMISTRY. 93 
 
 albumen of the food of the adult animal, rendered 
 soluble by digestion, and absorbed from the alimen- 
 tary canal by an apparatus provided for the purpose, 
 becomes in part changed to fibrin by the time it finds 
 its way into the veins to form new blood. 
 
 It is true that the identity of composition of the 
 albuminous principles has since been called in ques- 
 tion by M. Dumas, who has published a very elaborate 
 series of analyses, in which certain differences are 
 pointed out, apparently too large and too constant 
 to be considered the consequence of mere errors of 
 experiment. The subject thus imperatively demands 
 re : examination, as it is too important to be left in 
 doubt. 
 
 When either albumen, fibrin, or casein is dis- 
 solved in dilute caustic alkali, and the solution pre- 
 cipitated by a slight excess of acid, a large quantity 
 of white, flocculent matter separates, which may be 
 very easily collected upon a filter, washed, dried, 
 and subjected to examination. This body is the 
 u Protein" of Mulder ; it is the same in properties 
 from all three sources, while analysis shows it to 
 contain carbon, hydrogen, oxygen, and nitrogen, 
 exactly in the same proportions as we have them 
 in fibrin, albumen, and casein. 
 
 This most beautiful experiment may receive at 
 least two interpretations. We may suppose, with 
 the discoverer, that the new substance, the protein, 
 is really the common fundamental basis of the three 
 albuminous principles, which it forms by uniting 
 with certain small quantities of sulphur and phos- 
 phorus, or sulphur alone, and which latter bodies 
 
94 ANIMAL CHEMISTRY. 
 
 become separated by the alkali, and retained in so- 
 lution when the protein is precipitated by an acid ; 
 or \ve may, on the other hand, imagine that the 
 protein is a product of the action of the base, gene- 
 rated, in short, under its influence, in the same way 
 as stearic acid and glycerine may arise from a neu- 
 tral fat under similar circumstances, there not being 
 a tittle of evidence to show that either of these last- 
 named bodies pre-exist in the fat itself. Which- 
 ever view be adopted and it is a thing of no mo- 
 ment we cannot fail to be struck with the remarka- 
 ble support afforded by these experiments to the 
 doctrine of the partial identity of composition of 
 the protein-giving principles. This must suffice, al- 
 though much more might be said, for the albumin- 
 ous group. 
 
 The membranous and cartilaginous tissues, the 
 " cellular substance" of the body, all those portions 
 which dissolve in boiling water and furnish a jelly 
 on cooling, must now be notieed. A distinction is 
 drawn between membrane and cartilage, on the 
 ground that the one gives by boiling ordinary gela- 
 tine, and the latter a substance differing somewhat 
 from gelatine, to which the term " chondrin" has 
 been applied. 
 
 Gelatine, the properties of which in a state of 
 some purity are to a certain extent generally known 
 from its wide-spread applications, does not, it seems, 
 pre-exist in the animal body ; if it did, we should, 
 no doubt, find it in the blood, which is not the case, 
 from its ready solubility in warm water. It is be- 
 lieved to be produced by a specific chemical change 
 
ANIMAL CHEMISTRY. 95 
 
 of one or other of the albuminous principles by the 
 agency of oxygen drawn from the air. One of the 
 many possible representations of the nature of this 
 change is given at the end of the volume, which, it 
 must be remembered, is merely conjectural, as all 
 such representations at present must be, from want 
 of sufficient experimental evidence to give them a 
 higher claim to attention. 
 
 The substance of the brain and nerves appears 
 to be principally albumen, in a peculiar state, asso- 
 ciated with certain remarkable fatty substances, one 
 of which is said to contain a very large amount of 
 unoxidized phosphorus ; and, lastly, the bones, and 
 even the teeth, are constructed of cartilaginous ma- 
 terial, stiffened out and made hard and rigid by 
 earthy salts, principally phosphate of lime. 
 
 Such are the chief components of the animal 
 body. 
 
 Now it does not require much observation to 
 convince us that, so long as life continues, a per- 
 petual destruction, a never-ceasing waste of all 
 parts of the body is constantly going on. From 
 the first moment of our being to the termination of 
 our days, there is never, for a single instant, such a 
 thing as permanence of state. The various secre- 
 tions of the body are always in progress; oxygen 
 is absorbed into the system at each inspiration ; 
 water and carbonic acid are thrown off every time 
 the lungs collapse; the skin abandons, too, its quota 
 of these substances, which pass away in an invisible 
 form, and elude ordinary observation ; and what is 
 still more remarkable, the manifestations of living 
 
96 ANIMAL CHEMISTRY. 
 
 power, the amount .of nervous energy possessed by 
 the individual, is connected in some mysterious way 
 with this very waste and degradation itself. The 
 exertion of muscular power, the very exercise of 
 the mind itself, are, so far as we can judge, as inti- 
 mately bound up with change of matter, as the 
 evolution of electricity in the voltaic pile is with 
 the chemical action upon the metal with which the 
 instrument is constricted. 
 
 To compensate these continual losses, so de- 
 structive to the body, and yet so indispensable to 
 life itself, a formative power, like that possessed by 
 plants, has been communicated to the system, by 
 virtue of which repair is constantly made, with the 
 assistance of material furnished by the blood, which 
 thus not only becomes the channel by which de- 
 cayed and altered matter is withdrawn from the 
 body, but the very store-house and reservoir of 
 nourishment and support to every part of the 
 structure. 
 
 It is obvious, however, that the efficiency of the 
 blood for this most important purpose depends alto- 
 gether on the maintenance of its proper chemical 
 nature ; on the constant replacement from without, 
 in the shape of appropriate food, of the materials 
 abstracted from it in the renewal of the bodily frame, 
 and in the exercise of other functions, particularly 
 that of respiration. It is only in this way, by pre- 
 viously becoming blood, that food can be of any use ; 
 it must be capable of sanguification, or it cannot 
 fulfil the duties required from it. 
 
 The chemical history of the blood is exceedingly 
 
ANIMAL CHEMISTRY. 97 
 
 curious and interesting so far as it is understood. To 
 the naked eye, it presents the appearance of a ho- 
 mogeneous red, or dark purplish liquid, somewhat 
 viscid, and having a density considerably above that 
 of water. It has a saline and peculiar taste, and a 
 specific odour, which it very speedily loses. 
 
 When examined by a microscope of great power, 
 blood is seen to consist of multitudes of little round 
 red bodies, floating about in a nearly colourless liquid; 
 these are the " blood-globules," or " corpuscles" of 
 the physiologists, and to their number and minute- 
 ness the uniform red appearance of the whole is ob- 
 viously due. 
 
 There has been a great deal of dispute about the 
 figure and structure of these corpuscles ; the preva- 
 lent opinion seems to be that they are disc-shaped, 
 round, and flat, with a depression in the centre, 
 which in some positions of the light assumes the 
 appearance of a nucleus or little 
 transparent bead. It is probable, 
 however, that this is an optical 
 illusion ; it is only seen when 
 transmitted light is employed. 
 By reflected light the thickened 
 edges of the corpuscles are very 
 evident, and no nucleus can be 
 seen in the centre; they look like 
 the steel rings of a piece of mail. 
 It may seem strange to some that doubt and un- 
 certainty can exist about a simple matter of fact ; 
 but these bodies are very minute. In man they are 
 said to vary from c &,th to 3 ^th of an inch in diame- 
 5 
 
98 ANIMAL CHEMISTRY. 
 
 ter, and in some animals they are even smaller. 
 Microscopic investigations are beset with fallacies, 
 and in the most careful and experienced hands often 
 give equivocal and contradictory results. 
 
 The blood contains, in addition to the corpuscles 
 above described, great numbers of colourless glo- 
 bules, of still smaller dimensions, the nature of which 
 is very little understood. Some of these are cer- 
 tainly, however, composed of fat. 
 
 When a portion of blood is drawn from a living 
 animal into a shallow vessel, and left to itself for 
 some hours, it undergoes spontaneous coagulation in 
 a very complete manner ; it separates into a dark 
 red solid clot, and into a pale-coloured, slimy, saline, 
 and distinctly alkaline liquid which floats above. 
 This has already been mentioned as the chief de- 
 pository of albumen in the body. The effect des- 
 cribed is obviously caused by the solidification of the 
 fibrin, which, although constituting, when dry, a very 
 small portion of the whole, in the bulky and swollen 
 condition in which it separates, is voluminous enough 
 to entangle in its network of fibres the whole of the 
 colouring particles, thus carried down, and mechanic- 
 ally separated from the fluid which held them in 
 suspension. The production of the coaguhim in 
 blood is not the result of any formation of acid, as 
 in the case of milk, but arises simply from the dis- 
 tinguishing peculiarity of fibrin before described. 
 
 If the clot be drained as much as possible from 
 serum, by contact with bibulous paper, and then put 
 into water, the whole of the colouring matter dis- 
 solves, if time be allowed, and the white filaments 
 
ANIMAL, CHEMISTRY. 99 
 
 of fibrin left untouched subside to the bottom of the 
 vessel. The solution so obtained possesses a mag- 
 nificent crimson-red colour, and is found to contain 
 a substance which very closely resembles an ordinary 
 dye-stuff, like that of cochineal or logwood. It 
 gives coloured precipitate or " lakes," with alumina 
 and oxide of tin, and other substances used by the 
 dyer to fix his colours upon cloth, and is altogether 
 a very curious compound. Unfortunately, it is one 
 very difficult to study, from its great instability ; it 
 begins to decompose and change its hue after a very 
 short time : moreover, it is associated with some al- 
 bumen still remaining -behind, the separation of 
 which seems almost impossible. 
 
 The red colouring matter of the blood is thus 
 merely suspended in the serum ; not dissolved. In 
 water, the corpuscles break up and disappear ; but 
 in a strong saline solution, or a highly albuminous 
 liquid, they retain their integrity. The serum is a 
 liquid of this kind, or, rather, it is both saline and 
 albuminous, and in it consequently the little bodies 
 in question float about uninjured. Its state of dilu- 
 tion, however, is such as to approach very near the 
 point at which solution would occur ; for if a little 
 water be added, and the density of the liquid still 
 further reduced, the red discs begin to be attacked. 
 Now there can be no doubt but that the blood cor- 
 puscles, in a perfect and entire state, are in some 
 way intimately connected with the vital functions ; 
 what their office is, cannot at the present moment be 
 positively stated, although a conjecture on the subject 
 exists, and will be almost immediately mentioned. 
 
100 ANIMAL CHEMISTRY. 
 
 Their constant and uniform occurrence and peculiar 
 organization for the term may safely be applied 
 sufficiently indicate their importance. An adjust- 
 ment, therefore, has evidently been made of the 
 density of the blood-serum, and the amount of solid 
 matter contained in it, to the peculiar properties of 
 the corpuscles, in such a manner as to secure the 
 integrity of these latter, and at the same time retain 
 sufficient thinness and fluidity for the fulfilment of 
 the numerous duties required from it. 
 
 The red colouring matter has a composition ap- 
 proximating to that of the albuminous principles, 
 which it resembles in many other respects. It con- 
 tains, however, in addition to the elements of these 
 bodies, a component of a very peculiar nature, which 
 is found nowhere else in the system : this is the 
 metal iron. The proportion of iron is not a mere 
 trace, it makes up more than a twentieth of the 
 weight of the dry red substance. We cannot for 
 a moment suppose it to be accidental. 
 
 The mere presence of iron in blood is easily de- 
 monstrated. If a portion of that fluid be evaporated 
 to dryness and carbonized by a red -heat in a cruci- 
 ble, a black, spongy mass of coal will be obtained, 
 from which dilute acids extract abundance of oxide 
 of iron ; or, still more simply, by acting with a some- 
 what stronger acid upon dried clot, which readily 
 yields iron in this way. It has been usually stated 
 that the metal exists in blood in a very peculiar state, 
 a state in which it is not acted upon by ordinary 
 reagents ; but this is, to say the least, doubtful ; the 
 blood is alkaline, and alkalinity is incompatible with 
 
ANIMAL CHEMISTRY. 101 
 
 more than one of the most characteristic tests for iron. 
 There are many organic substances, which, added 
 to a salt of iron, altogether prevent its precipitation 
 by an alkali. Some of the vegetable acids have this 
 property. So that the mere fact of the alkaline solu- 
 ble condition is of itself no proof that the metal is not 
 in the state of oxide. 
 
 It is not easy to understand how this red matter, 
 or " hematosin," directly contributes to the building 
 up of the animal framework ; no organ or part of 
 the body contains iron in appreciable quantity as an 
 essential component ; and, besides, it seems unneces- 
 sary. We do not want it for this purpose, since the 
 blood contains, in a soluble state, abundance both of 
 albumen and fibrin, bodies appertaining to a class 
 from which alone, so far as appearance goes, the 
 various tissues and organs of the body have their 
 origin. Yet this substance must have some specific 
 office, because it is constantly observed that, in those 
 diseased states of the body in which the red particles 
 are deficient in quantity, the functions of life are lan- 
 guidly and imperfectly performed ; and, still further, 
 that this state is improved, and health amended, by 
 the administration in medicine of salts of iron. 
 
 Various ideas have been entertained on this sub- 
 ject by those devoted to physiological inquiries. 
 One only of these requires mention, in the present 
 instance, namely, that of Professor Liebig, who has 
 ventured to assign to the blood-corpuscles an office no 
 less important than that of serving as carriers of 
 oxygen from the lungs to all parts of the body ; a 
 power which he considers them to enjoy in virtue of 
 
102 ANIMAL CHEMISTRY. 
 
 the iron they contain. The following is a sketch of 
 this very beautiful and ingenious hypothesis. 
 
 The metal, iron, is known to form two* com- 
 pounds with oxygen : a protoxide and peroxide ; 
 the latter containing one half as much more oxygen 
 as the former. These two bodies, moreover, very 
 easily pass, under favourable circumstances, the one 
 into the other. If, for example, a salt of the pro- 
 toxide be mixed with caustic alkali in excess, the 
 precipitated proto-hydrate, at first nearly white, after 
 passing very quickly through various tints of green, 
 becomes foxy-red, or rust-coloured, and, if examined, 
 is found to be hydrate of the peroxide. This change 
 is caused simply by absorption of oxygen from the 
 air ; it commences at the surface of the mass, and 
 gradually creeps downwards until the alteration is 
 complete. Again, peroxide of iron, in contact with 
 many organic substances, is, with but little aid from 
 heat, deprived of a third of its oxygen, and thus re- 
 duced to the condition of protoxide; and these 
 changes may go on indefinitely, the metal being al- 
 ternately in either state, as the oxidizing or reducing 
 influences around it prevail. This is a property of 
 iron which exists to the same extent in no other 
 metal. 
 
 In the body there are two distinct kinds of blood ; 
 that of the veins, which is dark claret-coloured, 
 sometimes approaching to black, and that of the ar- 
 teries, which is always bright red. It is generally 
 
 * A third has quite recently been discovered, but this does 
 not interfere with the argument. 
 
ANIMAL CHEMISTRY. 103 
 
 well known, also, that the change from the venous to 
 the arterial condition is effected in the blood during its 
 passage through the minute capillary tubes which 
 ramify over the surface of each air-cell of the lungs. 
 This alteration, of which evidence is given by the 
 immediate change of colour, is certainly due to the 
 absorption of oxygen from without, and escape of 
 carbonic acid from within. These gases are con- 
 veyed through the thin wet membrane, in virtue of 
 their solubility in water, and not by any vital action; 
 it is an effect always observed with porous bodies in 
 general when thoroughly filled with liquid. The 
 opposite change, that from arterial blood to venous 
 is also known to occur in those equally minute ves- 
 sels or passages which unite the ultimate subdivisions 
 of the veins and arteries, and in which, whatever be 
 their nature, all the great functions of life are cer- 
 tainly carried on. 
 
 Such are the acknowledged facts. The use of 
 the iron is thus explained : In the bright red aerated 
 blood, the iron exists in the state of peroxide, its 
 highest degree of oxidation. So long as it travels 
 through the larger vessels this state is maintained. 
 It is in contact with de-oxidizing matter it is true, 
 but then the whole mass is loaded with dissolved oxy- 
 gen gas taken up in the lungs, which prevents any 
 thing like de-oxidation. By and by, however, by 
 the time the blood reaches the smaller branches of 
 the general arterial system, much of this free oxygen 
 has disappeared ; and at last, when it gets into the 
 capillaries themselves, the reducing power, appetite 
 for oxygen, or combustibility of the matter of the 
 
104 ANIMAL CHEMISTRY. 
 
 various parts and organs with which it is in contact, 
 becomes so high and energetic, that the loosely com- 
 bined oxygen is abstracted from the peroxide of iron, 
 and that substance reduced to protoxide, beyond 
 which, of course, it cannot go. The organic tissues 
 thus oxidized or burned produce carbonic acid, which 
 saturates the protoxide of iron, so that we have it in 
 the venous blood in the state of carbonate. 
 
 Now, moist proto-carbonate of iron exposed to 
 the air, readily gives up its carbonic acid, absorbs 
 oxygen, and passes to peroxide. This takes place in 
 the lungs, and accounts, in some measure at least, 
 for the large amount of that gas in the expired air. 
 
 Much of the oxygen which finds its way into the 
 system is, as just hinted, undoubtedly taken up by 
 the serum itself, in consequence of its solvent power. 
 The greater part of this, but not the whole, gets 
 converted into carbonic acid by the time the blood 
 reaches the great venous trunks, and afterwards 
 conveyed into the air by the false diffusion before 
 spoken of. 
 
 This is certainly a very beautiful theory of the 
 use of the iron. Whether it be true or not is 
 another question ; a question which cannot, at 
 present, be solved. Our means of experiment are 
 very far from permitting the determination of such 
 a problem one way or the other. On any supposi- 
 tion, however, a great part of the sketch given 
 must be true. The oxidation, the burning of the 
 substance of the body ; in other words, the change 
 of matter indispensable to every vital movement ; 
 the combustion of carbon and nitrogen, in short, in 
 
ANIMAL CHEMISTRY. 105 
 
 the blood takes place not in the lungs, but in the 
 capillary vessels of the whole body. Here is the 
 fire-chamber where the fuel is consumed, which is 
 destined to set in motion the whole machinery of 
 life. 
 
 The term furnace is used advisedly. It is with 
 premeditation and choice of terms that the capil- 
 lary system is compared to a fire-place. We must 
 disconnect the idea of combustion, in the larger 
 sense in which it is here employed, from that of 
 flame or ignition, where the heat evolved is intense. 
 There is no chemical doctrine more probable, but at 
 the same time, unfortunately, more difficult of de- 
 monstration, than that which declares the constancy 
 of the relation between chemical action and its 
 calorific effects. There is every reason to believe 
 that the same amount of chemical force always de- 
 velops the same quantity of heat. Whether that 
 heat be very gentle or very intense, is simply an 
 affair of time. A piece of iron, slowly rusting to 
 its centre in the atmosphere, develops, during its 
 oxidation, as much heat as an equal weight of the 
 metal in that minutely divided state in which it 
 burns on contact with air. In the one case, the ac- 
 tion is distributed, as it were, over a great length of 
 time ; in the other, it is completed in a moment. 
 As much heat however, has, without doubt, been 
 evolved in the one instance as in the other, only it 
 has been dissipated and lost as fast as it was pro- 
 duced, and never acquired sufficient intensity to at- 
 tract attention. The beautifully constant relations 
 of number and quantity between chemical and elec- 
 5* 
 
106 ANIMAL CHEMISTRY. 
 
 trieal, between electrical and magnetic forces, abso- 
 lutely forbid any other supposition, as at variance 
 with all the great laws pf the material world which 
 science has made known to us. 
 
 Carbon and hydrogen are burned in the blood, 
 and this to an extent which will strike with sur- 
 prise, and at first, incredulity, those unaccustomed 
 to such considerations. Many ounces of carbon 
 are, in every individual, daily rejected from the 
 lungs as carbonic acid. It is impossible that com- 
 bustible matter can thus be disposed of without the 
 evolution of a vast amount of heat ; as much heat, 
 in fact, as if it had been burned in a fire-grate. 
 This heat is manifest in the elevation of temperature 
 which the animal frame always possesses above that 
 of the surrounding medium ; an elevation of tem- 
 perature always in direct proportion to the amount 
 of nervous and muscular energy of the animal, and 
 to the vigor of its respiration, but never in any 
 single case altogether absent. 
 
 The internal capillary combustion is the source 
 of animal heat. 
 
 Thus much for the body. Every part where 
 blood-vessels are to be found ; every part where 
 nervous influence is perceptible ; every organ, every 
 tissue; muscle, and brain, and nerve, and mem- 
 brane, waste away like a burning taper, consume to 
 air and ashes, and pass- from the system, rejected 
 and useless ; and where no means are at hand for 
 repairing these daily and hourly losses, the indi- 
 vidual perishes dies more slowly, but not less 
 surely, than by a blazing pile. He is, to the very 
 
ANIMAL CHEMISTRY. 107 
 
 letter, burned to death at a low temperature ; the 
 various constituents of the body give way in suc- 
 cession ; first, the fat disappears ; this is the most 
 combustible, but at the same time the least essen- 
 tial ; it is sacrificed ; then the muscles shrink, and 
 soften, and decay. At last the substance of the 
 brain becomes attacked, and madness and death 
 close the scene. 
 
 This is starvation. 
 
 Among the most beautiful results of organic 
 chemistry must certainly be placed those which in- 
 struct us in the nature and functions of the food. 
 Much yet remains to be done before the subject can 
 be considered at all complete, and some of the most 
 interesting results are yet disputed ; but still enough 
 has been effected to shadow out certain general 
 principles in the highest degree worthy of atten- 
 tion. The first, most important, and, perhaps, best 
 established of these principles, admits of being laid 
 down in the form of a definite proposition. It is to 
 the following effect : 
 
 Those substances only are capable of being 
 employed in the renewal and repair of the 
 body, which have the same chemical compo- 
 sition as the body itself, or, which comes to 
 the same thing, as the blood, out of which 
 the body is constructed. 
 
 There are but three proximate organic principles 
 yet known which come within these terms ; those, 
 namely, already described albumen, fibrin, and 
 casein ; these only have the power of reproducing 
 
108 ANIMAL CHEMISTRY. 
 
 blood, and these only can afford nourishment and 
 support, in the strict sense of the term. 
 
 It is not meant that these bodies alone, in a state 
 of great purity, are all that can be required for the 
 due maintenance of the vital powers ; on the con- 
 trary, the experiment, cruel as it is, has been tried 
 repeatedly, and always with a negative result. 
 Certain non-azotized bodies seem to be essential 
 such as fat, or some substitute for fat, always present 
 in natural food. These alone, are still less capable 
 of supporting life than the unmixed albuminous prin- 
 ciples. Although such bodies are often but sparing- 
 ly furnished, they are always to be found. There 
 are other substances, too, required by the animal, 
 which, in small quantities, are as essential to its 
 well-being as the inorganic salts of the vegetable 
 kingdom are to the plant. Phosphates, ferruginous 
 matter, compounds of potash, soda, and lime, and 
 perhaps other things, are required. An animal can 
 no more live on albumen alone than a plant on car- 
 bonic acid alone ; in fact, there is a very close re- 
 semblance between the two cases. 
 
 The process of nutrition in animals that feed on 
 flesh is simple in the extreme ; the food consumed 
 is identical, in every respect, with the body for whose 
 nourishment it is designed. Arrived in the stomach, 
 it undergoes simple solution in the slightly acid se- 
 cretion of that organ, and then, as it passes through 
 the short and simple alimentary canal of these crea- 
 tures, it gets almost entirely absorbed, and at once 
 carried into the blood, nothing being rejected but the 
 comminuted bones and hair, and other insoluble rel- 
 
ANIMAL CHEMISTRY. 109 
 
 ics of the prey. The flesh of the animal devoured, 
 becomes by mere transposition, part and parcel of 
 that of its devourer. 
 
 So far all is simple and clear enough ; the ma- 
 jority of animals, however, do not live upon flesh, 
 but are, on the contrary, exclusively vegetable feed- 
 ers. We require to see how the law applies in this 
 case. 
 
 It is here that the unspeakable importance and 
 value of the vegetable albuminous principles, referred 
 to in an earlier part of this volume, becomes mani- 
 fest. These bodies are diffused throughout the whole 
 vegetable creation ; not a plant exists which does 
 not contain one or other of them. A few examples 
 may be cited ; it would be easy to extend their 
 number almost indefinitely. 
 
 The grain of the cereals is rich in azotized mat- 
 ter of this kind, which may be separated by an ex- 
 ceedingly simple mechanical process. The meal is 
 mixed with water to a paste and patiently washed, 
 either in the hand or on a fine metallic sieve, until 
 the whole of the starch has been carried away, and 
 the liquid runs clear ; there then remains behind an 
 adhesive, elastic substance, long known under the 
 name of " gluten." If this gluten be now boiled with 
 strong alcohol, a small quantity of a peculiar sticky 
 matter is dissolved out, together with some fat, and 
 there remains a white, stringy-looking body, which, 
 when carefully examined, is found to be absolutely 
 identical in every respect, both in properties and 
 composition, with the fibrin of the animal frame. 
 This vegetable fibrin is found in wheat-flour to the 
 
110 ANIMAL CHEMISTRY. 
 
 extent of eight or ten per cent., and is the principal 
 cause of the high value of wheaten bread as an 
 article of food. 
 
 Again, if the juice of any green plant be taken, 
 filtered to render it clear, and then exposed to heat, 
 a substance separates in little flocks, which, when 
 collected, dried, and boiled in ether to remove certain 
 impurities soluble in that liquid, exhibits all the 
 characters and composition of boiled white of egg. 
 This is vegetable albumen, and it is to be found 
 throughout the whole vegetable world. 
 
 Once more : it has been discovered that beans 
 and almonds, and a great variety of seeds, often con- 
 tain, in addition to one or both of the above-men- 
 tioned substances, a third, which is identified with 
 animal casein. 
 
 There is no difficulty, then, in understanding how 
 it is that animals live upon plants ; these plants al- 
 ready contain, ready-formed, the principal materials 
 of their bodies, which only require to be separated 
 and brought into a soluble state to become blood. 
 The function of nutrition is in every respect the same 
 as in those creatures that live upon flesh. 
 
 Now, however, comes a very remarkable differ- 
 ence between the food of these animals and that of 
 the carnivora, which consists of pure flesh and merely 
 a little fat. Vegetables contain but a comparatively 
 small portion of azotized matter ; the great bulk of 
 their substance is made up of woody-fibre, or starch, 
 or gum, or something of the kind, destitute of nitro- 
 gen. These things cannot form blood ; cannot, 
 directly at least, nourish the body. 
 
ANIMAL CHEMISTRY. Ill 
 
 In a flesh-eating animal the destruction of the 
 tissues of the body is very rapid indeed, a& the char- 
 acter of the excretions fully demonstrates ; the tem- 
 perature of the body is in a great measure kept up, 
 and vitality maintained, by the burning of flesh and 
 nerve. This rapid decay is, however, compensated,- 
 and equilibrium maintained, by an abundant supply 
 of highly azotized food, capable of rapid and com- 
 plete assimilation. 
 
 Such is not the case in the graminivora ; the 
 supply of these protein compounds is but slender, and 
 requires to be economized to the utmost. They con- 
 stitute a fuel too costly to be burned to any great 
 extent. We find, however, associated with these 
 azotized matters, a very large quantity of saccharine 
 or starchy substances, which disappear in the body 
 completely. Taking all these things into account, 
 the conclusion drawn by Liebig appears perfectly 
 inevitable namely, that the non-nitrogenous con- 
 stituents of the food of these animals, whether it be 
 starch, or sugar, or fat in any shape, is exclusively 
 employed in the'generation of animal heat in econ- 
 omizing, in short, the more essential components of 
 the body by becoming burned in their place. 
 
 We thus get a division of the whole food into 
 two distinct classes of substances those, namely, 
 which are devoted to the repair and nutriment of the 
 body, and those whose duty it is to furnish animal 
 heat by their combustion in the blood. Among the 
 former, called by Liebig, " plastic elements of nutri- 
 tion," we find 
 
112 ANIMAL CHEMISTRY. 
 
 Vegetable fibrin, 
 Vegetable albumen, 
 Vegetable casein, 
 Animal flesh and blood; 
 
 and among the latter, or " elements of respira- 
 tion" 
 
 Fat, Grape-sugar, 
 
 Starch, Milk-sugar, 
 
 Gum, Mucilage, 
 
 Cane-sugar, Wine, beer, spirits. 
 
 These constitute fuel-food, and are of no other use. 
 
 A few remarks on the quantity of carbon actu- 
 ally consumed in one day in the body of man, and of 
 one or two of the larger quadrupeds, will suffice to 
 terminate this general sketch of the subject. 
 
 Two distinct and wholly dissimilar methods of 
 inquiry have been foPowed in this investigation, and 
 both are unfortunately attended with great practical 
 difficulties of execution. The results, nevertheless, 
 tally sufficiently well with each, and induce us to 
 place considerable confidence in their accuracy. 
 
 The first method that followed by nil the earlier 
 experimenters consists in determining directly, by 
 careful analysis of the expired air, the quantity of 
 carbonic acid discharged from the lungs in a given 
 time ; then, if the disengagement of gas be supposed 
 uniform, the quantity daily produced admits of easy 
 calculation. 
 
 There are several important fallacies, however, 
 in this plan. In the first place, breathing conducted 
 through a tube connected with a gas-holder, which 
 
ANIMAL CHEMISTRY. 113 
 
 was the system generally practised, must be very 
 different from breathing in the open air. The in- 
 spirations and expirations are much deeper when the 
 attention is directed to the process. It is not unlikely 
 that this error maybe, to a considerable extent, com- 
 pensated by their diminished frequency, and the ulti- 
 mate result thus rendered more correct than the pro- 
 cess seemed to promise. Again, the production of 
 carbonic acid is by no means uniform throughout the 
 day. Dr. Prout* found it to vary considerably at 
 different times, being greatest at noon, during gentle 
 exercise, and least of all in the depth of sleep. This 
 is precisely what we should expect to find from the- 
 oretical views, and the fact has since received exper- 
 imental corroboration. 
 
 The lungs constitute, it is true, by very far the most 
 important channel by which carbonic acid escapes 
 from the body. There is another, notwithstanding, 
 in the skin, which, in these experiments, is altogether 
 neglected. The whole surface of the body disen- 
 gages the gas in question ; a fact which must always 
 be taken into account. 
 
 There have been many able experimenters engag- 
 ed on this subject. In the Philosophical Transactions 
 for 1808, will be found, for example, an exceeding- 
 ly interesting memoir by Messrs. Allen and Pepys. 
 The experiments were made at the Royal Institution. 
 It was concluded, that " a middle-sized man, aged 
 about thirty-eight years, and whose pulse is 70 on 
 an average, gives off 302 cubic inches of carbonic 
 acid in 11 minutes; and supposing the production 
 
 * Quoted by Berzelius Lehrbuch, 9, p. 125. 
 
114 ANIMAL CHEMISTRY. 
 
 uniform for 24 hours, the total quantity in that peri- 
 od would be 39,534 cubic inches." 
 
 Now, 39,534 cubic inches of carbonic acid weigh 
 18,683 grains, and contain 5166 grains of carbon, 
 or 10*7 ounces troy. 
 
 The estimate of Sir H. Davy* agrees very closely 
 with the preceding namely, 26*6 cubic inches per 
 minute, or 38,304 cubic inches in the day. This 
 quantity will weigh 18, 102 grains, and contain 5006 
 grains of carbon, or 10'4 ounces troy. 
 
 The close coincidence of these experiments both 
 with each other, and also with some of more recent 
 date in which the sources of error adverted to were 
 guarded against, is very remarkable. 
 
 Dr. Scharling has lately put in practice a modifi- 
 cation of the same method. The person experi- 
 mented upon was inclosed in an air-tight wooden 
 chest, sufficiently capacious to enable him to remain 
 a considerable time without inconvenience, and fol- 
 low a variety of occupations, and even sleep. A 
 glass window was fitted to the chest. By suitable 
 contrivances a slow but constant supply of pure air, 
 freed from carbonic acid, was passed into the appara- 
 tus during the whole period of each experiment, and 
 at its exit conducted through a strong solution of 
 caustic potash contained in an ordinary Liebig's ap- 
 paratus, by which the proportion of the gas thus car^ 
 ried away was easily estimated. Lastly, the air of 
 the chest itself was carefully analyzed at the com- 
 mencement and termination of each experiment, and 
 
 * Memoirs, 3, p. 255. 
 
ANIMAL CHEMISTRY. 115 
 
 corrections duly made in the calculated results for 
 alterations of pressure and temperature. 
 
 The usual duration of an experiment was about 
 an hour. They were made upon a variety of per- 
 sons, and at various periods of the day and night, in 
 the hope of obviating the errors arising from changes 
 in the state of the body. 
 
 The variations in the quantity of carbonic acid 
 given off were very considerable. During sleep, 
 and when fasting, it was at its minimum, and after 
 a meal invariably highest. Children exhaled more 
 carbonic acid, in proportion to their weight, than 
 adults. The following are Dr. Scharling's general 
 conclusions respecting the quantities of carbon ac- 
 tually disengaged, in the course of twenty-four hours, 
 by each of the six persons undermentioned, upon 
 whom the experiments were made. It is assumed, 
 that, in the case of the children, nine hours were 
 passed in sleep, and in that of the adults seven hours : 
 
 1. A man, 35 years old, weighing 131 Danish Ibs., gave off in 
 
 the time mentioned 3386 grains of carbon=7.05 oz. troy. 
 
 2. A young man of 16, weight 115j Ibs, 3462 grs.=7-21 oz. 
 
 3. A soldier, 28 years old, weight 164 Ibs. 3698 grs.=7-07 oz. 
 
 4. A girl of 19, weighing 111J Ibs. 2559 grs.=5-33 oz. 
 
 5. A boy of 9f years, weight 44 Ibs. 2054 grs.=4-28 oz. 
 
 6. A girl of 10 years, weight 46 Ibs. 1935 grs.=4-03 oz.* 
 
 Several years ago, M. Boussingault devised, and 
 put into practice with great ingenuity, a form of 
 experiment for the purpose of solving a very im- 
 
 * Annalen der Chemie und Pharmacie, 45, p. 214. 
 
116 ANIMAL CHEMISTRY. 
 
 portant problem in agriculture science, which he 
 afterwards applied to animal physiology. 
 
 The problem was to determine the relative quan- 
 tities of food furnished to cultivated plants by the 
 earth and by the air, and the plan proposed for its 
 solution was as follows : During the whole time of 
 one rotation, a period extending over five years, an 
 exact account was kept of the quantity and chemi- 
 cal composition of the manures spread upon a 
 marked extent of ground, and of the different crops 
 raised from it, using all precautions to prevent error 
 from varying quantities of water in the different sub- 
 stances examined, and conducting the analyses with 
 great care. At the end of the period referred to, on 
 comparing the total amount of carbon, hydrogen, 
 nitrogen, oxygen, and inorganic matters contained 
 in the plants raised, with that furnished to the land 
 in the shape of manure, it became easy to see how 
 much of these bodies the earth and the air had re- 
 spectively furnished. A simple subtraction would 
 give the information required. 
 
 Just in the same way, if it be required to deter- 
 mine the quantity of carbon and hydrogen daily 
 burned to carbonic acid and water in the body of an 
 animal, it is only necessary to compare by analysis 
 the proportion of those substances given in the food 
 with that contained in the excretions of the animal 
 itself. The difference between these will obviously 
 represent the quantity consumed in respiration. 
 
 M. Boussingault* experimented on a cow and a 
 horse ; his principal object at the time was to settle ' 
 
 * Annales de Chitnie et de Physique, Ixxi., p. 113. 
 
ANIMAL CHEMISTRY. 117 
 
 the disputed point of the absorption or non-absorp- 
 tion of nitrogen from the air by animals, which he to 
 a great extent effected, by showing that in an ani- 
 mal so supplied with food that its weight remains for 
 a long time unchanged, the nitrogen contained in 
 that food always exceeds that voided in the excre- 
 tions. At the same time an opportunity was afforded 
 for examining the amount of carbon lost, by the aid 
 of a similar comparison. 
 
 It was found that in twenty-four hours the cow 
 consumed in respiration the enormous quantity of 
 seventy ounces of carbon, and the horse seventy- 
 seven ounces. Professor Liebig has lately applied 
 Boussingault's method to the human subject. His 
 mean result indicates an expenditure of about four- 
 teen ounces of carbon daily, for well-fed, healthy 
 men employed in labour in the open air, as soldiers : 
 the amount is much smaller in those who lead a de- 
 pressed or sedentary life. 
 
 The diet-tables of the Royal Navy furnish the 
 means of making an approximation to the quantity 
 of carbon required for the respiratory process, in cir- 
 cumstances extremely favourable to its activity. As 
 no very accurate determination has been made of 
 the per-centage of carbon in the different articles, 
 the numbers given must not be looked upon as 
 absolutely correct ; it is probable, however, that they 
 are not far from the truth. 
 
 TABLE I. Daily allowance to each man. (Salt provision.) 
 
 oz. carbon. 
 
 16 oz. biscuit, at 41 per cent, carbon . = 6-56 
 12 salt meat, at 20 per cent, carbon . = 2 40 
 
118 ANIMAL CHEMISTRY. 
 
 12 oz. flour at 40 per cent, carbon . . = 4-80 
 
 1 " cocoa 70 " " . . . = -70 
 
 1-5 " sugar 42 " " '.'/'. '".' = -63 
 
 1509 
 Or 13-75 ounces troy. 
 
 TABLE II. Daily allowance to each man. (Fresh provisions.) 
 
 oz. carbon. 
 
 16 oz. biscuit, at 41 per cent, carbon . = 6-56 
 
 16 " fresh meat at 15 per cent, carbon = 2-40 
 
 1 " cocoa 70 " " . = -70 
 
 1-5 . sugar 42 " " . = -63 
 
 8 " vegetables . . . ck^i.^ = '80 
 
 Or lO'l ounces troy. 
 
 If we are content to assume, with Liebig, that 
 the small quantity of carbon found in the excretions 
 is compensated by that contained in the beer or 
 spirits, and other trifling articles furnished to the 
 men, but omitted in the table, then the numbers will 
 really represent the amount employed in respiration. 
 
 On the whole, it seems probable that this method 
 of experiment, carefully followed, will give more 
 trustworthy results than the first described ; it is no 
 doubt both laborious and disagreeable, but its value 
 is great. 
 
 M. M. Andral and Gavarret* have very recently 
 published a series of interesting experiments on the 
 same subject, not yet, however, complete, in which 
 they seek to establish the influence of age, sex, and 
 other circumstances, upon the production of carbonic 
 acid by respiration. The maximum quantity of 
 
 * Ann. Chim. et Phys., 3d series, viii , p. 129. 
 
ANIMAL CHEMISTRY. 119 
 
 carbon exhaled by a young and healthy man, is 
 stated at about 217 grains per hour, or 13 ounces 
 troy daily. 
 
 The preceding brief notice of the general nature 
 of animal nutrition, will, it is hoped, put the reader 
 into a position to consider with advantage certain 
 remarkable cases of the special adaptation of the 
 chemical nature of the food to the circumstances of 
 the individual for whose use it is designed. 
 
 The bodily frame and constitution of the human 
 race have been so adjusted as to admit of the main- 
 tenance of life and health under a variety of circum- 
 stances truly surprising. Extremes of heat and cold, 
 of moisture and dryness, are borne with impunity so 
 long as the habits and mode of life of the individual 
 remain in accordance with his physical condition. 
 
 In tropical countries where the high temperature 
 of the air, and the abundance of aqueous vapour it 
 contains, develop to the utmost the resources of veg- 
 etable life, the amount of personal labour required 
 for self-support is extremely trifling. The heavy 
 and laborious culture of the temperate regions, the 
 unceasing tillage of the soil, so necessary with us, 
 are altogether uncalled for. In those smiling regions 
 of almost, perpetual sunshine, where the teeming 
 earth gives its increase with the least possible toil 
 on the part of the cultivator, and all Nature invites 
 to repose and indolence, the energies of the mind 
 itself are unstrung- by the removal of that sharp spur 
 of necessity which goads men to the task of labour, 
 until exertion becomes a habit, which carries them 
 onward beyond their immediate wants, and impels 
 
120 ANIMAL CHEMISTRY. 
 
 them to seek the permanent improvement and exalta- 
 tion of their state. The sustenance furnished to the 
 human race by a wise and bountiful Providence has 
 been so adjusted, chemically, to this condition of 
 things, as involuntarily to excite in the observer the 
 deepest feelings of admiration and gratitude. 
 
 Where the temperature of the air approaches 
 within a few degrees that of the body, the genera- 
 tion of animal heat by the burning of organic matter 
 in the blood may be reduced in amount. Where 
 muscular power and motion are less required and 
 less employed, the waste of the body is diminished 
 in the same ratio ; a comparatively small quantity of 
 food, both for fuel and for nutriment, is, in such a 
 case, required. The stomach, however, must be 
 filled, the uneasy sensation of want must be remov- 
 ed ; and this has been done. In the rice, and fruits, 
 and other products of the countries in question, we 
 find a food extremely agreeable to the taste, but 
 possessing little sustaining power; much of it is mere 
 water, and the solid portion itself is chiefly made up 
 of neutral non-azotized bodies, containing oxygen 
 and hydrogen in the proportions to form water ; 
 bodies which, in burning, furnish far less heat than 
 those in which carbon and hydrogen greatly predom- 
 inate. The azotized portion of the food of hot coun- 
 tries is always very small in comparison with the 
 rest ; it is, however, sufficient for the purpose of 
 repairing the trifling daily loss the body sustains. 
 The desire for animal food is very slight, and often 
 is altogether absent. 
 
 The North American hunter lives wholly upon 
 
ANIMAL CHEMISTRY. 
 
 flesh ; he patiently follows the footmarks of his game 
 through the wild woods for days together, until he 
 finds an opportunity of surprising it ; fasting mean- 
 while, or, at best, subsisting on a few scraps of dried 
 meat ; rivalling the beast of prey in his power of 
 endurance in his quick, yet stealthy step, and in 
 the searching glance of his eye ; careless alike of 
 frost and heat, sleeping on the bare ground, a thin 
 blanket or a buffalo-robe his only protection. It is 
 his food which enables him to do and to suffer all 
 this: to bear exertions which would destroy him 
 were he not supported from within by a kind of 
 nourishment so concentrated in its form as to supply 
 abundantly during the period of repose, the losses 
 of bodily substance, the deficiencies occasioned by 
 change of matter; and even to render the exertions 
 themselves, violent and continued as they are, actu- 
 ally sources of pleasure. 
 
 It is not by any peculiarity of physical constitu- 
 tion that the Indian is enabled to bear hardship, and 
 fatigue, ;and privation, which to us appear extraor- 
 dinary ; the European, under similar circumstances, 
 and under a similar regimen, exhibits the same re- 
 markable powers. The hunters and trappers, em- 
 ployed by the fur companies of British America, 
 lead a still harder life. These men are, as is well 
 known, accustomed to disperse themselves, often 
 singly, along the rivers and streams, the haunts of 
 the beavers and other animals they seek to capture ; 
 a rifle, and flint and steel their only household goods, 
 without shelter in the midst of a trackless wilder- 
 ness, often suffering the extremities of cold and hun- 
 
ANIMAL CHEMISTRY. 
 
 ger, subsisting entirely on the flesh of the creatures 
 they succeed in taking, and this for months together, 
 until each has collected the number of skins he 
 deems sufficient to repay his labour, or the fast-fall- 
 ing snows of approaching winter drive him to seek 
 the protection of the trader's fort. 
 
 And yet this wild existence is said to possess a 
 charm of its own, powerful enough to bind, to the 
 end of their days, those who have once practised it ; 
 the unbroken solitude of the lake and the river, the 
 freedom of the desert, and even the very dangers of 
 the pursuit, have their own peculiar attraction. The 
 men themselves, when not cut off prematurely by 
 starvation, or any other of the common accidents of 
 this life, or murdered by the Indians whose vengeance 
 they have provoked by their aggressions, live to 
 old age, exempt from a host of sorrows and afflic- 
 tions known to a more luxurious race, and perhaps, 
 on the whole, enjoy as much real happiness as com- 
 monly falls to the lot of man. 
 
 Take, again, the condition of the Esquimaux, in 
 his hut of ice-blocks or driftwood, his only food the 
 seal and the walrus, which he spears with his bone- 
 pointed weapon, from a little frail coracle of skins. 
 The air is cold enough to freeze quicksilver ; he 
 wraps himself in his dress of furs, and forth he goes 
 with perfect impunity, and the cold of the shore of 
 the frozen sea affects him less than that of a chilly 
 January day does the Englishman by his warm fire- 
 side. Yet the Esquimaux has no fireside ; he cooks 
 his food by the heat of a lamp fed with oil, the pro- 
 duct of the chase ; his country produces no fuel, and 
 
ANIMAL CHEMISTRY. 123 
 
 he cannot think of devoting the few fragments of 
 wood, brought by the ocean currents from more fa- 
 voured climes, which he finds upon the sea beach, to 
 this purpose ; they are far too valuable to be so em- 
 ployed. How, then, it may be asked, is he capable 
 of supporting this intensity of cold ? the peculiarity 
 of his food furnishes the reply. 
 
 We are accustomed to look with horror and dis- 
 gust at the food of these poor people, as we in our 
 ignorance and presumption dare to call them ; to 
 commiserate the taste of those who, as our northern 
 navigators relate, prefer a piece of tallow candle, or 
 a draught of train-oil, to the fare of an English man- 
 of-war ; but a little more consideration might, per- 
 haps, show us that the blubber and fat of the arctic 
 cetacea and fish, the only food the inhabitants of 
 these countries can obtain, really constitute the only 
 sort of food which could enable them to bear up 
 against the extremities of cold to which they are 
 subject. There is no other substance but fat, and 
 that in very large quantity, which would answer the 
 purpose required ; it is a substance exceedingly rich 
 in hydrogen, and in the body eminently combustible; 
 weight for weight, it will generate a far larger 
 amount of heat, when burned in the blood, than any 
 thing else which can be taken as food. It will be 
 wiser, then, instead of condemning, as filthy and ab- 
 horrent, the tastes and propensities of the Esquimaux, 
 to consider them as a special adaptation, by an un- 
 speakably benevolent Providence, of the very wishes 
 and inclinations of the individual to the circumstan- 
 ces of his life. 
 
124 ANIMAL CHEMISTRY. 
 
 But this is not all ; the same individual, who, 
 when in a warm or temperate climate, craves a large 
 proportion of bread and vegetable food, and turns 
 with aversion from fatty substances, experiences, 
 when transported to the frozen regions of the north, 
 a complete revolution in his tastes and desires. 
 Nothing will then satisfy him but fat ; the flesh of 
 deer, fish, to be acceptable, must be loaded with fat ; 
 he takes delight in sucking the marrow from the 
 bones; nothing in the shape of grease comes amiss 
 to him ; he longs for it, he desires it as much as he 
 formerly loathed it. But this new, this induced state, 
 only lasts as long as his mode of life requires ; re- 
 moval to a milder region restores, to a very great ex- 
 tent, the first condition. 
 
 This" is no imaginary statement; it is perfectly 
 authentic, and serves to place in a novel and striking 
 point of view the power of accommodation to cir- 
 cumstances possessed by man. 
 
 The very occupations which the people of ex- 
 cessively cold countries are compelled to follow, are 
 connected, in the most intimate manner, with the 
 nature of their food. They are invariably such as 
 to require great bodily exertion. Now this is al- 
 ways attended by increased respiration the breath- 
 ing is deeper and much more frequent ; and again, 
 from the superior density of the cold air, a larger 
 weight is at each inspiration taken into the lungs; 
 more oxygen is thus carried into the system, the 
 fuel-food is rapidly consumed, and animal heat is 
 rapidly evolved. It is not enough that the furnace- 
 bars be piled with fuel, unless means exist for in- 
 
ANIMAL CHEMISTRY. 125 
 
 creasing the supply of oxygen for its combustion ; 
 and this is done by compelling the person to occupy 
 himself with the chase of wild animals, instead of 
 following the more staid and quiet life of a herds- 
 man or a tiller of the soil. 
 
 In the nutriment whieh has been provided for 
 the young of the human race, and of the higher 
 classes of animals, we have the most perfect type of 
 food in general that it is possible to give. Provision 
 for this helpless condition of life has been made with 
 the most tender care ; the finding of suitable food 
 has not been left to chance, but a supply has been 
 provided, of a kind and in a manner to impress alike 
 upon the giver and the recipient a placid enjoyment 
 of happiness, perhaps not surpassed by any thing on 
 earth, and calculated at the same time, from its very 
 peculiar chemical nature, to afford every principle 
 required for the development of the body of the little 
 one for whom it is destined. 
 
 The reader will find, in the appendix, a detailed 
 account of the composition of milk, so far as it is at 
 present known ; there are one or two points which 
 yet require .to be elucidated, but enough is apparent 
 to indicate how eminently it is fitted for the object 
 to be fulfilled. 
 
 It will be seen that the characteristic and lead- 
 ing constituent of milk, casein, is present in large 
 quantity, and in a soluble state ; now this casein is 
 identical in composition with the muscular substance, 
 and with the albumen of the blood. It is easy to 
 see its use. By a molecular change, of the simplest 
 kind, it becomes the material of flesh, or passes into 
 
126 - ANIMAL CHEMISTRY. 
 
 cellular tissue and membrane, by an act of oxidation. 
 We find, besides, associated with this casein, a large 
 quantity of earthy phosphates, held in solution in a 
 very extraordinary manner, in a neutral, or even 
 slightly alkaline menstruum, and which evidently 
 offer the greatest facilities to a most important pro- 
 cess at this period of life in great activity, that of 
 the formation of bone. Neither have the elements 
 of respiration been neglected ; in childhood, this 
 function is exceedingly energetic, and accordingly 
 no less than two non-azotized bodies have been pro- 
 vided for this purpose, and both upon a very liberal 
 scale butter and sugar of milk ; these burn in the 
 body to carbonic acid and water, and develop the 
 necessary heat. The saline constituents of milk, 
 even the trace of ferruginous matter it contains, are 
 equally useful, although less conspicuous ; nothing 
 superfluous is to be found, and nothing essential to 
 the well-being of the infant has been omitted. 
 
 Much good would ensue if these simple and ra- 
 tional views of the nature and functions of food were 
 carried out into general practice ; how often do "we 
 see the evident dictates of nature perverted and set 
 aside in favour of customs and habits prejudicial in 
 the highest degree ! 
 
ON 
 
 THE RELATION BETWEEN PLANTS AND 
 ANIMALS. 
 
 RELATIONS of the most intimate kind link togeth- 
 er the two great classes of organized beings ; be- 
 tween the vegetable and the animal kingdoms a bond 
 of mutual dependence may be traced exceedingly in- 
 teresting to contemplate. Although the general na- 
 ture of the relations may be, in great part, inferred 
 from statements already made, it will be proper to 
 collect and reconsider them before terminating the 
 whole subject. 
 
 The food of plants is entirely inorganic ; carbo- 
 nic acid, water, ammonia, and certain salts of metal- 
 lic oxides, are, so far as we know at present, the only 
 substances capable of being employed by them as 
 food. When other bodies such as decaying organic 
 matter seem to be efficacious in this respect, they 
 are so only from their property of easily undergoing 
 changes which end in the production of the bodies 
 mentioned. Vegetables have the power of decom- 
 posing these exceedingly stable compounds, and re- 
 arranging their elements in such a way as to gener- 
 ate bodies so complex in constitution that they often 
 
128 ON THE RELATION BETWEEN 
 
 baffle our endeavours to represent them and their re- 
 actions by exact chemical formulas. It is by a pro- 
 cess of de-oxidation, in the first instance, that these 
 things are brought about a process which we do 
 not understand, and cannot imitate. The production 
 of albumen or sugar in a plant is at present a com- 
 plete chemical mystery, which we have not yet been 
 able to penetrate ; perhaps we never may, but the 
 fact is not the less certain. 
 
 Animals are exclusively nourished by matters 
 already organized \ matters which are, as already 
 stated, often identical in composition with the sub- 
 stance of .their bodies, or at least always capable of 
 becoming so by chemical changes of a simple and 
 intelligible nature, the analogs of those we are in the 
 habit of producing at will in the laboratory. The 
 animal body is constantly in a state of decay from 
 the chemical action of the oxygen introduced in res- 
 piration. The products of this decay are, at first, 
 employed in the system, in various ways, as their 
 nature permits, and, after passing through many suc- 
 cessive stages of decomposition, are finally rejected 
 from the body in the form of carbonic acid, and water, 
 and urea a substance allied to, and readily becom- 
 ing, carbonate of ammonia. 
 
 No contrast can be greater than that presented 
 by the chemistry of vegetable and of animal life. In 
 the one case we have a set of changes occult and 
 refined in the highest degree, incomprehensible in 
 their nature although evident in their effects, the re- 
 sult of which is. the production of organic matter out 
 of inorganic ; in the other, we have these same or- 
 
PLANTS AND ANIMALS. 
 
 129 
 
 ganic substances gradually passing by a descending 
 scale into compounds less and less complex, by 
 changes which we can in most instances understand, 
 and in some imitate, until they at length reach the 
 inorganic condition, and once more become capable 
 of assimilation by plants. A perpetual and unbroken 
 chain of vital phenomena is thus established, the pro- 
 ducts of the one order of beings becoming the susten- 
 ance of the other. 
 
 A recent French writer has contrasted these op- 
 posite functions of plants and animals in a very pleas- 
 ing manner.* 
 
 THE VEGETABLE 
 
 Produces the neutral azotized 
 substances, 
 
 fatty sub- 
 stances, 
 
 sugar, starch, and 
 
 gum, 
 
 Decomposes carbonic acid, 
 
 water, 
 
 ammoniacal salts, 
 
 Disengages oxygen, 
 
 Absorbs heat and electricity, 
 
 Is an apparatus of reduction, 
 
 Is stationary. 
 
 THE ANIMAL 
 
 Consumes the neutral azo- 
 tized substances, 
 
 fatty 
 
 substances, 
 
 sugar, starch, and 
 
 gum, 
 
 Produces carbonic acid, 
 
 water, 
 
 ammoniacal salts, 
 
 Absorbs oxygen, 
 
 Produces heat and electricity, 
 
 Is an apparatus of oxidation, 
 
 Is locomotive. 
 
 The removal of carbonic acid from the atmos- 
 phere is effected by the agency of plants ; there 
 are so many sources of this poisonous gas in con- 
 stant activity, that, were no means in existence for 
 its withdrawal from the air, the latter would become 
 
 * Annales de Chim. et Phys., Dec. 1842. 
 6* 
 
130 ON THE RELATION BETWEEN 
 
 in the end unfit for respiration. It is true that, on 
 any supposition, a great length of time must elapse 
 before such a state of things would arrive ; thou- 
 sands of years would probably pass before the pro- 
 portion of carbonic acid had risen to such an extent 
 as to exert a perceptible influence ; the atmosphere 
 is so vast, of such immense volume, that an altera- 
 tion of this kind must occur very slowly. It is 
 difficult, however, to say how small an increase of 
 the gas might prove hurtful to animal existence 
 when its effects were continued, as they necessarily 
 would be, upon many successive generations ; it is 
 difficult to estimate the minimum quantity of poison 
 necessary to destroy health and vigour in a creature 
 for a very long period subjected to its influence. 
 Besides, all the arrangements of nature bear the 
 impress of stability upon them; where perturbing 
 causes appear to exist, compensation is sure to be 
 discovered if diligently sought. It would be con- 
 trary to the analogy of the whole to imagine that a 
 principle were in operation whose ultimate effect 
 would be to render the earth uninhabitable. Car- 
 bonic acid is fatal to all animals; its deleterious 
 powers are not merely exerted on a few all alike 
 perish when exposed to its action. It may be, and, 
 indeed, very probably is, a part of the great design, 
 that successive races of animals should, in turn, in- 
 habit this earth for a certain period, each perishing 
 after a time, and giving place to another, like wave 
 following wave upon the surface of the sea. Man 
 is but a creature of yesterday ; his dwelling-place 
 was once the abode of animals, now only known to 
 
PLANTS AND ANIMALS. 131 
 
 us from their remains entombed in the solid earth, 
 and the time may come when his race shall wither 
 away and disappear, like the ichthyosaurus and the 
 iguanodon of old. The permanence of the life of a 
 race may have as little existence as that of an indi- 
 vidual ; the destruction of the capability of the earth 
 to support life at all is a very different matter. 
 
 The same reasoning leads to doubt the supposi- 
 tion which some have entertained of a gradual 
 diminution in the quantity of carbonic acid contained 
 in the air at an earlier period of the history of the 
 earth, when the plants of the great coal formation 
 lived and flourished. The reason assigned for this 
 idea is found in the great development of their leaves 
 in comparison with their roots ; plants, resembling 
 the ancient species, are still, however, abundant in 
 the warmer regions of the earth, although the air in 
 those localities is not richer in carbonic acid than it 
 is in Europe. 
 
 In whatever light we consider these matters, the 
 argument of benevolent design and contrivance, de- 
 duced from the obvious facts themselves, remains 
 unaltered. The care and beneficence of the Creator 
 is not less shown in the connexion he has established 
 between physical and moral health. The labour 
 which a man is obliged to exert to procure for him- 
 self the necessaries of life is not less essential to the 
 maintenance of a healthy tone of mind than of a 
 sound and active condition of the bodily organism. 
 That labour should be the lot of the human race, 
 instead of being, as some have represented it, a 
 curse, is, in fact, the highest blessing that 
 
132 ON THE RELATION BETWEEN 
 
 have been bestowed. No evil can be greater than 
 the rust, alike of body and soul, which results from 
 inactivity. The state of labour is the very condition 
 of enjoyment ; not, indeed, the excessive and slavish 
 toil to which a very large portion of mankind have, 
 by a most unfortunate combination of circumstances, 
 been reduced, but that moderate and well-regulated 
 labour of mind and body, which conduces so much 
 to the welfare of both, and which would be, under 
 more favourable auspices, fully sufficient to impart 
 comfort and abundance to all. If men only knew 
 and felt how inseparably their own individual happi- 
 ness is connected with the welfare and prosperity of 
 their species; if those who have intellect, and 
 power, and wealth at their disposal, could only be 
 persuaded to thrust aside the petty jealousies and 
 cares, the idle parade and prejudices of society, and 
 join heart and hand in the great work of human im- 
 provement, how much might be effected! How 
 much happier and how much better all might become 
 if a sound and universal spirit of philanthropy were 
 once awakened, capable of embracing within its 
 pale all orders and conditions of men, considering- 
 them, as they really are, the children of one com- 
 mon Parent, bound together by the ties of brother- 
 hood, each having a special duty assigned to him to 
 perform, not independently of, but in conjunction 
 with, the rest, and exciting all to render each other 
 mutual assistance in surmounting the difficulties and 
 trials of this life of discipline and pupilage. 
 
 The first and most indispensable condition of 
 happiness to a reflecting, intelligent man, must be 
 
PLANTS AND ANIMALS. 133 
 
 the acquisition of sound, consistent, and cheerful 
 views of the relation in which he stands to his Crea- 
 tor ; without these, all external appliances and means 
 are worthless. Unless he be deeply impressed, tho- 
 roughly imbued, with the conviction that he is, and 
 shall be, every moment of his existence in the hands 
 of a Being of unmixed and unbounded benevolence, 
 exerted under the guidance of wisdom and know- 
 ledge, embracing all possible contingencies, and ren- 
 dered effective by power extending to all things not 
 involving contradiction, he cannot be permanently 
 happy. It is melancholy to reflect upon the evils 
 which have been brought upon the earth by the 
 adoption of narrow and false ideas of God and of 
 his attributes. The great and beneficent Creator 
 has been invested with the passions and infirmities 
 of humanity. He has been represented as delight- 
 ing in the exercise of mere arbitrary power ; as ca- 
 pricious and revengeful ; as exercising a kind of fa- 
 vouritism towards particular individuals, and suffer- 
 ing the rest to remain in a state of hopeless misery. 
 Men have sought, in the figurative language of 
 Scripture, confirmation of these views, and have not 
 scrupled to indulge their own evil nature in persecu- 
 ting their fellows under the mask of religious zeal. 
 Even those whose sincerity and purity of motive 
 are altogether above suspicion, have been led to the 
 perpetration of acts from which, under other circum- 
 stances, they would have recoiled with horror. 
 
 The attributes of the Deity have been constantly 
 placed in opposition to each other. Good men have 
 laboured to reconcile justice and mercy, as if they 
 
134 ON THE RELATION BETWEEN 
 
 could ever be at variance ! All this arises from a 
 misunderstanding of the general principle of benevo- 
 lence : from confounding two things essentially dis- 
 tinct namely, real, provident goodness, and w r eak, 
 short-sighted indulgence. The true type of God's 
 government is to be found in that exercised by a 
 wise and good parent over his children. He corrects 
 them when necessary by the infliction of pain, and 
 stimulates them to improvement by the hope of plea- 
 sure or reward ; but the motive is the same in both 
 cases. It is an enlightened, active benevolence 
 which prompts him to punish where punishment is 
 needful. To withhold this would be any thing but 
 an act of mercy. The dealings of God towards man 
 are of this character. We have the positive assurance 
 of One who spake as never man spake, while the 
 analogies of nature, and the silent conviction of our 
 own souls, testify to the truth of this greatest and 
 most important of all doctrines. 
 
 It is by such fatal misconceptions that so many 
 worthy and earnest men have been driven into fa- 
 naticism on the one hand, or infidelity on the other; 
 to abandon the light of reason altogether as a 
 most treacherous guide, or to cast away the authority 
 of inspiration, and justify the act by insisting on the 
 repugnancy of its dogmas t<r the best and noblest 
 feelings of the human heart. What better and more 
 obvious plan can be devised for preventing such de- 
 plorable mistakes than that of making the works of 
 the Creator the commentary and exponent of his 
 written word ? May not the light of nature thus 
 employed, by exhibiting in all their generality and 
 
PLANTS AND ANIMALS. 135 
 
 magnificence the great fundamental truths which 
 form the basis of all sound and harmonious religion, 
 become a key to a number of apparent anomalies in 
 Holy Writ, which perplex and harass the mind of 
 the inquirer 1 
 
 What is the object of all science ? Is it to pro- 
 cure the means of increased indulgence and refine- 
 ment in the luxuries and the arts of life that we seek 
 to extend the boundaries of natural knowledge ? Is 
 the discovery of abstract principles only desirable on 
 account of the possible application of these principles 
 to the attainment of wealth and power 1 It cannot 
 be by any such considerations that the philosopher 
 is urged forward in his painful and thorny path of 
 discovery. It is rather by an irresistible impulse, 
 an instinct of his nature, which prompts him to re- 
 joice in the contemplation of physical truth for its 
 own sake, and to take delight and pleasure in its de- 
 velopment. It would be improper to underrate the 
 value to mankind of the thousand beautiful applica- 
 tions of scientific principles to the purposes of daily 
 life, but it is false to assume that these are other 
 than subordinate to the one great object of all the 
 elevation and improvement of the mind itself. No- 
 where throughout the whole creation is the goodness 
 of the Almighty more conspicuous than in the means 
 he has provided for revealing himself to his intelli- 
 gent creatures, by conferring upon them these very 
 powers of discovering truth, arid of appreciating its 
 beauty and loveliness. 
 
APPENDIX. 
 
 I. 
 
 ON THE EXISTENCE OF PHOSPHORIC ACID IN 
 ROCKS OF IGNEOUS ORIGIN. 
 
 THE reasons mentioned in the body of the Essay 
 induced the author to suppose that many mineral 
 bodies of volcanic origin might be found to contain 
 traces of phosphoric acid ; a substance easily over- 
 looked, unless suspicion of its presence exists, and 
 special search is made for it. The properties of 
 phosphate of alumina so much resemble those of the 
 pure earth, that, unless the experimenter be very 
 much upon his guard, he is very likely to be led into 
 error. 
 
 The first substance examined was pure white 
 porcelain clay, the result of the decomposition of 
 felspar, from Dartmoor, Devon. It gave, on analysis 
 by the usual method, in 100 parts 
 
 Silica 47-20 
 
 Alumina, with trace of iron and manganese 38-80 
 
 Lime -24 
 
 Water 12- 
 
 Alkali and loss 1 76 
 
 100. 
 
APPENDIX. 137 
 
 A quantity of dry clay in powder, amounting to 
 1000 grains, was boiled several hours in a flask, with 
 dilute hydrochloric acid, mixed with a large volume 
 of distilled water, and allowed to remain at rest until 
 the following day. The clear and highly acid liquid 
 was next decanted from the sediment, evaporated to 
 a small bulk, and super-saturated with pure ammo- 
 nia. The precipitate, collected on a small filter, 
 washed, dried, carefully separated from the paper, 
 and heated to redness, was next reduced to powder, 
 and intimately mixed with an equal weight of pure 
 silica and six times as much dry carbonate of soda. 
 This mixture was fused in a platinum crucible. When 
 cold, the melted mass was dissolved out with boiling- 
 water, and placed upon a filter to separate the inso- 
 luble silicate of alumina and oxide of iron. The 
 filtered solution was next rendered acid by nitric acid, 
 evaporated to dryness, treated with water, rendered 
 exactly neutral by a drop or two of ammonia, and 
 again filtered. The solution so obtained, gave, on 
 the addition of nitrate of silver, a beautiful pale 
 yellow precipitate, soluble both in ammonia and 
 acetic acid j and, on being mixed with some hydro- 
 chlorate of ammonia and a little excess of caustic 
 ammonia, furnished, with a drop of solution of sul- 
 phate of magnesia, an abundant crystalline white 
 precipitate, characteristic of the presence of phos- 
 phoric acid. 
 
 These results, which were perfectly unequivocal, 
 were obtained again and again ; the distilled water 
 and re-agents employed were examined with the 
 utmost care, and every precaution was taken to avoid 
 
138 APPENDIX. 
 
 an accidental introduction of the substance sought. 
 It will be observed that filtration of acid liquids was 
 always avoided, lest a trace of phosphate should be 
 dissolved from the paper, and the experiment thus 
 vitiated. 
 
 A similar portion of the crumbling decomposed 
 granite, from the same locality, on being subjected 
 to the foregoing process, gave distinct evidence of 
 phosphoric acid. 
 
 The phosphoric acid is probably in combination 
 with alumina. 
 
 Sound and unaltered crystallized pink felspar, 
 from Germany, was reduced to a fine powder in a 
 mortar of Swedish porphyry, and examined by the 
 same method. The result was a failure ; the mineral 
 was too hard to be acted upon by dilute acid. 
 
 Two hundred grains of the same substance were 
 then fused, in a platinum crucible, with six hundred 
 grains of dry carbonate of soda ; the mass treated 
 with water and filtered. The solution, after the 
 silica had been separated, gave but equivocal symp- 
 toms of the presence of phosphoric acid. 
 
 It is probable that by acting on the powdered 
 mineral with hydrofluoric acid, the phosphoric acid 
 may be found in the unchanged felspar as readily 
 as in the decomposed mineral. The want of a pla- 
 tinum retort for preparing the hydrofluoric acid, pre- 
 vented the experiment. 
 
 Dark-coloured vesicular lava from the Rhine, 
 now quarried for the purpose of completing the 
 cathedral of Cologne, powdered in the porphyry 
 mortar, and treated in the same manner as the por- 
 
APPENDIX. 139 
 
 celain clay, yielded not mere traces of phosphoric 
 acid, but abundance ; enough to perform the ex- 
 periments by which its presence was made known 
 upon a large scale. This is, no doubt, part of the 
 secret of the extraordinary fertility of certain soils 
 derived from the decomposition of lava. 
 
 White trachyte, from the Drachenfels, near 
 Bonn, on the Rhine, subjected to a similar method 
 of treatment, gave up a large quantity of phos- 
 phoric acid. This rock is chiefly composed of. 
 glassy felspar. 
 
 Red scoriaceous lava, from Vesuvius, reduced to 
 fine powder and boiled with dilute hydrochloric 
 acid, was acted upon to a considerable extent. 
 The solution contained much phosphoric acid. 
 
 It would be worth while repeating the search 
 for this substance, not only in felspar, but in mica 
 and hornblende, using perhaps hydrofluoric acid to 
 disintegrate the minerals. When a very large mass 
 of salt is present, as in the unsuccessful experiment 
 before described, the trace of phosphate escapes 
 detection. 
 
 II. 
 
 ON THE RELATIONS OF GRAPE-SUGAR, MILK-SUGAR, AL- 
 COHOL, AND LACTIC ACID. 
 
 The very general use of chemical formula?, and 
 their adoption into every elementary work on the 
 subject, induce the hope that the symbolical lan- 
 guage almost of necessity made use of in this part 
 of the volume, will be intelligible. The equation 
 
140 APPENDIX. 
 
 is such a convenient mode of representing chemical 
 changes and relations of composition, and tends so 
 much to brevity and clearness, that its advantages 
 are acknowledged by all. 
 
 It will be merely necessary to remind the reader 
 that the letters C, H, O, N, &c., indicate equiva- 
 lents of carbon, hydrogen, oxygen, and nitrogen, 
 the number of which is pointed out by the small 
 appended figure. When the letter alone is used, 
 one equivalent is meant. 
 
 (a.) Vinous fermentation. 
 
 (2 equiv. alcohol . . C H O 
 8 12 4 
 4 equiv. carb. acid . C O 
 
 4 8 
 
 2 equiv. water . . HO 
 2 2 
 
 C H O 
 
 12 14 14 
 
 (6.) Conversion of milk-sugar into lactic acid. 
 
 f 2 equiv. lactic acid . C H O 
 
 Crystallized milk-sugar, \ 12 10 10 
 
 C H O 1 2 equiv. water . . HO 
 12 12 12 I 22 
 
 C H O 
 
 12 12 12 
 
 The mode of conversion of grape-sugar .into 
 lactic acid will be obvious from the foregoing. It 
 is stated that cane-sugar cannot itself ferment, and 
 that, when this seems to occur, it is always by first 
 passing into the state of grape-sugar. 
 
APPENDIX. 
 
 141 
 
 III. 
 
 COMPOSITION OF ALBUMEN, FIBRIN, AND CASEIN, FROM 
 THE ANIMAL BODY. 
 
 The analyses of Mulder are quoted from the 
 Lehrbuch of Berzelius, and those of Dr. Scherer 
 from his paper in the Jinnalen der Chemie und 
 Pharmacie 9 vol. xxxix. The memoirs of M. Du- 
 mas is to be found in the December number of the 
 Jlnnales de Chimie et de Physique, 1842. 
 
 (a.) Albumen. 
 
 Carbon 
 Hydrogen 
 Nitrogen 
 Oxygen . 
 Phosphorus 
 Sulphur . 
 
 54-84 
 
 7-09 
 
 15-83 
 
 21-23 
 
 From eggs. From serum. 
 
 55-000 . . . 55 097 
 
 7 073 . . . 6-880 
 
 15920 15-948 
 
 w 
 
 33 ^ ... 
 64 J 
 
 100- 
 
 22-007 
 
 100- 
 
 22-075 
 
 100- 
 
 The following are the mean results of two sets 
 of experiments by Dumas : 
 
 From human serum. From eggs. 
 
 Carbon .... 53-32 . . . 53-37 
 
 Hydrogen . . . 7-29 . . . 7-10 
 
 Nitrogen . . . 15 70 ... 15-77 
 
 Oxygen . . . 23-69 V.% .* 23-76 
 
 100- 
 
 100- 
 
142 
 
 Carbon. . 54-56 . 
 
 Hydrogen . 6'90 . 
 
 Nitrogen . 15-72 . 
 
 Oxygen . 22-13^ 
 Phosphorus '33 >. 
 Sulphur . -36 J 
 
 100- 
 
 APPENDIX. 
 
 (6.) Fibrin. 
 
 SCHERER. 
 
 
 . . 54 454 . . . 
 . . 7-069 . . . 
 . . 15-762 . . . 
 
 55 002 . . . 
 7-216 . . . 
 15 817 . . . 
 
 54-976 
 6-867 
 15-913 
 
 22-715 
 
 100- 
 
 21-965 
 
 100- 
 
 . . 22-244 
 
 100- 
 
 Dumas gives, as the composition of human 
 fibrin 
 
 Carbon 52-78 
 
 Hydrogen 696 
 
 Nitrogen 16-78 
 
 Oxygen, sulphur, and phosphorus . 23 48 
 
 100- 
 
 (c.) Casein. 
 
 Carbon . . 
 
 54-96 . . . 
 
 54721 
 
 . . . 54 665 
 
 . . . 54-580 
 
 Hydrogen . 
 
 7 15 . . . 
 
 7-239 
 
 . . . 7-465 
 
 . . . 7-352 
 
 Nitrogen . 
 
 15-80 . . . 
 
 15-724 
 
 . . . 15 724 
 
 ... 15 699 
 
 Oxygen . . 
 Sulphur . . 
 
 21-73) 
 .36 5 ' ' ' 
 
 22-316 
 
 . . . 22-146 
 
 . . . 22-372 
 
 100- 
 
 100- 
 
 100- 
 
 100- 
 
 According to Dumas, on the contrary, casein of 
 cow's milk contains 
 
 Carbon 53 50 
 
 Hydrogen 7-05 
 
 Nitrogen 15-77 
 
 Oxygen and sulphur 23 68 * 
 
 100- 
 
APPENDIX. 
 
 143 
 
 (d.) Protein. 
 The following are Mulder's results : 
 
 From -vegetable 
 albumen. 
 
 From 
 fibrin. 
 
 From 
 albumen. 
 
 From 
 casein. 
 
 Carbon . . . 
 
 54-99 . . . 
 
 5544 
 
 . . . 55-30 . . . 
 
 55.159 
 
 Hydrogen . . 
 Nitrogen . . 
 Oxygen . . 
 
 6 87 . . . 
 15 66 . . . 
 
 22-48 . . . 
 
 6-95 
 16-05 
 21-56 
 
 . . . 6-94 . . . 
 . . . 16-02 . . . 
 ... 21-74 ... 
 
 7-176 
 15-857 
 
 21-808 
 
 100- 
 
 100- 
 
 100- 
 
 100- 
 
 Dr. Scherer's experiments afforded 
 
 
 From crystalline 
 
 From 
 
 From 
 
 
 lens. 
 
 albumen. 
 
 fibrin. 
 
 Carbon . . 
 
 . 55 300 . . . 
 
 55-160 . . . 
 
 54-848 
 
 Hydrogen . 
 
 . 6 940 . . . 
 
 7-055 . . . 
 
 6-959 
 
 Nitrogen . 
 
 . 16-216 . . . 
 
 15-966 . . . 
 
 15-847 
 
 Oxygen 
 
 . 21 544 . . . 
 
 21-819 
 
 22-346 
 
 100- 
 Dumas gives 
 
 Carbon . . . 
 Hydrogen . 
 
 Nitrogen . . 
 
 Oxygen . . 
 
 100- 
 
 100- 
 
 From albumen. 
 
 54-38 
 
 7-14 
 
 15-92 
 
 2256 
 
 100- 
 
 The results of the analyses of MM. Mulder and 
 Scherer will be seen to coincide in a manner won- 
 derfully complete when the difficulties attending such 
 experiments are taken into consideration. M. Dumas 
 will hardly be justified in applying to the evidently 
 careful researches of Dr. Scherer the term, u An- 
 alyses executees avec une facheuse precipitation et 
 tout-a-fait incorrectes." The subject must still be 
 considered open to investigation. 
 
144 APPENDIX. 
 
 IV. 
 
 COMPOSITION OF ALBUMEN, FIBRIN, AND CASEIN, 
 FROM THE VEGETABLE KINGDOM. 
 
 Fibrin, from Wheaten Flour. (Dr. Bence Jones.*) 
 
 Carbon 53-83 
 
 Hydrogen 7-02 
 
 Nitrogen 15-58 
 
 Oxygen, sulphur, and phosphorus . . 23-57 
 
 100- 
 Protein, from the foregoing. (Dr. Scherer.f ) 
 
 i. ii. 
 
 Carbon .... 54663 . . . 54-617 
 
 Hydrogen . . . 7-302 . . . 7-491 
 
 Nitrogen . . . 15-810 . . . 15.809 
 
 Oxygen .... 22-285 '. .... 22083 
 
 100- 100- 
 Vegetable Casein. 
 
 DR. SCHERER.t DR. BENCE JONES. 
 
 Carbon .... 54-138 . . . 55-05 
 
 Hydrogen . . . 7-156 . . . 7-59 
 
 Nitrogen .... 15 672 . . . 15 89 
 
 Oxygen and sulphur 23 034 . . . 21-47 
 
 100- 100- 
 
 Vegetable Albumen. (Dr. Jones. ||) 
 Carbon ...... 54 74 
 
 Hydrogen ..... 7-77 
 
 Nitrogen . . ... . 15 85 
 
 Oxygen, &c. ... . 21-64 
 
 100- 
 
 * Annalen der Chemie und Pharmacie, 40, p. 65. 
 t Idem, 40, p. 7. J Idem, 40, p. 8. 
 
 Idem, 40, p. 67. || Idem, 40, p. 66. 
 
APPENDIX. 
 
 145 
 
 V. 
 
 COMPOSITION OF THE BLOOD. 
 
 The following statement of the composition of 
 healthy human blood will serve to convey to the 
 reader an idea of the relative proportions of its com- 
 ponents. Such analyses are useful, although it must 
 be observed that they can only be considered as rudely 
 approximative, from the practical difficulties of the 
 inquiry. It is on the authority of M. Lecanu. 
 {Annales de Chimie et de Physique, xlviii. 320.) 
 
 Water , . . . 780-145 
 
 Fibrin. .-; '\ -'; ; '*| / ; "".' ; ; . 2-100 
 
 Albumen, . ,,, ( '*><,., . -, ,,, .-: ., . 65-090 
 
 Colouring matter . . . ". .'..' . 133-000 
 
 Crystallizable fat . . . i, . . . 2-430 
 
 Oily fat . . ' ^ i . . 1-310 
 
 "Extractive," soluble in water and 
 
 alcohol . . . . ....... . :;..,,, 1-790 
 
 Albumen, in union with soda . . . 1-265 
 Chlorides of sodium and potassium ; 
 
 alkaline carbonates, phosphates, 
 
 and sulphates 8-370 
 
 Carbonates and phosphates of lime, 
 
 magnesia, and iron . w . V 2-100 
 
 Loss ... ..,.;. - 2'400 
 
 1000- 
 
 785-590 
 
 3-565 
 
 69-415 
 
 119.626 
 4-300 
 2-270 
 
 1-920 
 2-010 
 
 7-304 
 
 1414 
 2-586 
 
 1000- 
 
 The earthy and alkaline carbonates mentioned in 
 the analyses probably exist in the state of organic 
 salts in the blood. 
 
 The ultimate composition of blood, as a whole, 
 is curious. It is precisely the same as that of mus- 
 7 
 
146 APPENDIX. 
 
 cular flesh. Ox-blood was dried by exposure to 
 gentle warmth in a silver vessel, and compared by 
 analysis with the lean flesh of the same animal also 
 carefully dried.* 
 
 Blood in 100 parts. Muscle in 100 parts. 
 
 Carbon . . . 51-950 51-965 . . . 51 83 51-893 
 
 Hydrogen . . 7-165 7-330 . . . 7-56 - 7-590 
 
 Nitrogen . . 17-172 17-173 ... 17-15 17-160 
 
 Oxygen, &c. . 19-295 19-115 . . . 19-23 19 127 
 
 Ashes . . . 4-418 4.413 . . . 4 23 4-230 
 
 Flesh is, in fact, organized blood; and blood 
 fluid flesh. 
 
 VI. 
 
 ON THE FORMATION OF GELATINOUS TISSUE. 
 
 It becomes us to speak very cautiously respecting 
 the exact nature of the change by which the protein 
 compounds are made, by an act of oxidation in the 
 body, to yield the gelatinous tissues ; which latter, in 
 all probability, have the same composition as the 
 gelatin they give when boiled in water, or only 
 differ, at least, in the elements of water. The 
 simplest formula for protein is, according to Mulder, 
 C H N ; and that of gelatin, on the same author- 
 
 40 31 5 12 
 
 ity, C H N O. Doubling these last numbers, and 
 
 13 10 2 5 
 
 supposing thirty-four equivalents of oxygen to be 
 consumed in the process, we may venture to repre- 
 sent, by the following equation, what may be sup- 
 posed to take place. The ammonia probably takes 
 the form of urea. 
 
 * Drs. Play fair and Boeckmann. See Liebig and Poggen- 
 dorf 'a HandicOrterbuch der Chemie, art. " Blut." 
 
Protein C H N O 
 
 40 31 5 12 
 -{-34 eq. oxygen O 
 34 
 
 APPENDIX. 147 
 
 fGelatin . . , C H N O 
 
 26 20 4 10 
 1 eq. ammonia H N 
 3 
 1 14 eq. carb. acid C O 
 
 14 28 
 
 8 eq. water . H O 
 I 88 
 
 CHNO CHNO 
 
 40 31 5 46 40 31 5 46 
 
 VII. 
 
 
 ON THE GENERATION AND USE OF PAT IN THE 
 
 ANIMAL SYSTEM. 
 
 The non-azotized constituents of the food, em- 
 ployed in man and the herbivora, and, to a smaller 
 extent, in the flesh-eating animals, in the genera- 
 tion of heat in the body, are of two kinds, name- 
 le, fatty substances, and neutral principles contain- 
 ing oxygen and hydrogen in the proportions to form 
 water. The use of these latter is, of course, ex- 
 clusively confined to the vegetable feeders. 
 
 That the fat which has actually been deposited 
 in the body from its superabundance in the blood, 
 can be again re-absorbed and disappear from the 
 system, is a truth too obvious to need discussion ; 
 and that this disappearance is due to the act of 
 respiration, is amply evidenced by the state in 
 which the elements of the substance issue from the 
 body namely, that of carbonic acid and water. It 
 is also a thing of common observation, that the 
 amount of bodily exercise taken by the animal in- 
 fluences to a very great extent the secretion of fat, 
 which is promoted by rest and inactivity, and hin- 
 
148 APPENDIX. 
 
 dered by all causes which exalt the respiratory 
 function, or depress the nervous system. 
 
 A much more difficult question is that of the 
 origin of the animal fatty principles. In the first 
 place, it is to be remarked that, taken as a class, 
 the bodies of carnivorous animals are much more 
 deficient in fat than those of the vegetable feeders, 
 in which it often abounds, as we well know, to a 
 great extent. Now, there are obviously but two 
 modes by which the occurrence of this substance 
 can be explained namely, to imagine that it has 
 been introduced ready formed by the food, or that it 
 has been generated in the body itself out of some 
 other substance so introduced. The first of these 
 opinions is held by the French school ; the second 
 is that of Professor Liebig, who assigns to the 
 starchy and saccharine portions of the food of the 
 graminivora, which remain in excess after the per- 
 formance, of the respiratory function, the duty of 
 actually producing fat by undergoing a change, the 
 analog of the vinous fermentation. 
 
 Jn support of this opinion, a number of facts, 
 well known to agriculturists and graziers, are 
 brought forward to prove the power possessed by 
 amylaceous food in the economical fattening of 
 cattle and other animals, which appear, at first sight, 
 to furnish evidence of the most conclusive nature hi 
 favour of the view held by the great German 
 chemist. 
 
 On the other hand, it is alleged that all vegeta- 
 ble substances usually employed for food contain 
 fatty matters, which can be extracted from them by 
 
APPENDIX. 149 
 
 suitable means, and this to a very far greater extent 
 than has hitherto been admitted ; to an extent, in 
 short, fully sufficient to account for the presence of 
 all the fat found in the body of the animal after 
 death, or separated from it in the milk-secretion 
 during life. 
 
 It is with this inquiry, as with many others of 
 far greater importance to the world at large : a 
 question which at first appears extremely easy to 
 solve, frequently assumes during the progress of the 
 investigation an air of far greater complexity than 
 we were prepared to expect. Things taken for 
 granted in the first instance, as well known matters 
 of fact, begin to be called in question. Proof is 
 demanded of the veracity of propositions of old and 
 established standing, and the inquirer often finds 
 himself compelled to begin de novo, and build up 
 his argument with materials drawn from his own 
 resources of experiment or observation. 
 
 We knew of old that traces of fatty substances 
 were to be found in, perhaps, all vegetable pro- 
 ducts, but we were hardly prepared to meet with 
 them to so great an extent in the common food of 
 the domestic animals, as the experiments of MM. 
 Dumas, Boussingault, and Payen indicate.* The 
 following are some of the most curious of their 
 results : 
 
 Vegetables. . Fat in 100 parts. 
 
 Maize, as a whole * . 8-75 
 
 Rice . . . > 1- 
 
 * See Annales de Chimie et de Physique, vol. viii. p. 63. 
 Third Series. 
 
 7* 
 
150 APPENDIX. 
 
 .Oats ... .; l'<r , ..... . u .>:,;;. 33 
 
 African Wheat . ? .. ,, ; . ; ^. . . . 2-1 
 
 Venezuela wheat 2'6 
 
 Fine wheat flour . . . . l v '. .... 1-4 
 
 Bran from the same 4-65 
 
 Dry hay 3- to 4 
 
 Straw of African wheat . .,. .., . v > . *-/ 32 
 
 Lucern (dry?) . . . . _ . '\. '. . . . . . 3'5 
 
 Oat straw . : . . 5-1 
 
 Tares 2- 
 
 Beet-root, moist . -05 
 
 Potatoes, moist . ,.r. r ..,-, . ( . j, *..',,. ' 8 
 
 If these large numbers really represent the av- 
 erage proportion of fat in the above-mentioned arti- 
 cles of agricultural produce, it may indeed be need- 
 less to resort to any hypothesis of the formation of 
 that substance in the body. The whole question 
 evidently turns upon this single point, which, of 
 course, can only be decided by a very extended 
 series of most accurate experiments. 
 
 It is proper to observe that the fatty matter 
 contained in plants is very often of a kind resem- 
 bling wax ; and it is rather doubtful how far such 
 a substance can become converted into ordinary fat. 
 ' A portion certainly passes through the body un- 
 changed. On the other hand, we have as yet no 
 proof that starch or sugar can suffer the alteration 
 before alluded to, either in the body or out of it. 
 
 VIII. 
 
 ON THE COMPOSITION OF MILK. 
 
 The following statement of the composition of 
 
APPENDIX. 151 
 
 fresh cow-milk is deduced from the recent experi- 
 ments of Haidlen :* 100 parts contain 
 
 Water . . - 88-3 
 
 Casein . > ,H:?>V :*fv > .f, 'jfl;*,\ \ <' 4-82 
 
 Milk-sugar . \ ^., 3'39 
 
 Butter . . . , ;;;;.;.> .... 3- 
 
 Phosphate of lime -231 
 
 magnesia -042 
 
 iron -007 
 
 Chloride Potassium -144 
 
 sodium '024 
 
 Soda (in union with casein) .... '042 
 
 100- 
 
 It is stated by Mulder, and others, who have 
 made casein the subject of their inquiries, that this 
 body, separated by precipitation from milk, contains 
 no unoxidized phosphorus ; a substance present in 
 both fibrin and albumen. Now, it is very certain 
 that milk alone is fully competent to the nourish- 
 ment of a young animal ; that is to say, to the pro- 
 duction of every part of its body, including those 
 which contain phosphorus in the state referred to. 
 Either, therefore, the animal system must have the 
 power of de-oxidizing phosphoric acid a thing 
 little probable or some yet unknown source of 
 phosphorus exists in milk which has escaped ob- 
 servation.. 
 
 It is curious to observe the manner in which the 
 earthy phosphates are held in solution in milk by the 
 joint assistance of the casein and the free alkali. 
 (See the paper just quoted.) 
 
 * Annalen der Chemie und Pharmacie, 45, p. 263. 
 
152 APPENDIX. 
 
 IX. 
 
 ON THE ARGUMENT OF DESIGN DEDUCED FROM THE 
 STUDY OF THE LAWS OF CHEMICAL COMBINATION. 
 
 It is possible that an argument of great force 
 and value may be based upon the peculiarities of the 
 laws which determine chemical union, without refer- 
 ence to any hypothetical views of the constitution 
 of matter. 
 
 The following is a very brief notice of the laws 
 themselves : 
 
 (a.) Laws relating to simple combination by 
 weight, four in number. 
 
 1. All chemical compounds are definite in their 
 nature, the ratio of the elements being constant. 
 
 2. When a body is- capable of uniting with a 
 second in several proportions, these propor- 
 tions bear a simple relation to each other. 
 
 3. If a body, A, unite with other bodies, B, C, D, 
 the quantities in which B, C, D, unite with A, 
 represent also the relations in which they unite 
 among themselves. 
 
 4. The combining quantity of a compound is the 
 sum of the combining quantities of its ele- 
 ments. 
 
 A few words of explanation will suffice to render 
 the purport and bearing of these laws intelligible. 
 
 The first law is almost self-evident : it is quite 
 natural to expect constancy of composition in the 
 same substance, however produced. The converse 
 of the proposition, however, is very far from being 
 
APPENDIX. 153 
 
 true, since the same elements uniting in the same 
 proportions do not necessarily generate the same 
 body. The large class of isomeric compounds are 
 examples of this most interesting fact ; for in these 
 we often have the greatest imaginable diversity of 
 character associated with absolute identity of com- 
 position. These bodies belong nearly all to organic 
 chemistry, and consequently result from the very 
 peculiar properties of carbon, hydrogen, nitrogen, 
 and oxygen, upon which much stress has been laid. 
 
 The second law is very simple, and yet very 
 important; it exhibits a remarkable relation always 
 found to obtain between closely allied compounds of 
 the same substances. The oxides of nitrogen afford 
 an exceedingly beautiful illustration of the rule in 
 its simples tform. These oxides are five in number, 
 and possess the . undermentioned composition by 
 weight : 
 
 Nitrogen. Oxygen. 
 
 Nitrous oxide .... 14-1 ... 8 
 
 . Nitric oxide 14-1 ... 16 
 
 Nitrous acid 14-1 ... 24 
 
 Peroxide of nitrogen . . 14-1 ... 32 
 
 Nitric acid 14-1 ... 40 
 
 So that, taking a constant quantity of the one ele- 
 ment in each case, the proportions of the other 
 increase by multiples of the first term 8, 8 x 2, 
 8 x 3, 8 x 4, &c. The same fact is evident in a 
 vast number of other instances : carbonic acid con- 
 tains exactly twice as much oxygen in proportion 
 to the carbon as carbonic oxide ; the red oxide of 
 mercury contains twice as much oxygen as the gray 
 
154 
 
 APPENDIX, 
 
 oxide, &c. Neither is the law limited to elementary 
 substances ; it regulates the formation of salts. Of 
 the three oxalates of potash, the second contains 
 twice as much acid as the first, and the third four 
 times as much, the quantity of the base being equal. 
 It is not always, however, that the relation is so 
 simple as that of one to two, or one to four ; two to 
 three is very common ; two to seven is sometimes 
 met with, but rarely. Other proportions are occa- 
 sionally seen, but it is often doubtful whether the 
 substances to which they belong are direct com- 
 pounds of their constituents. The oxides of iron 
 and manganese furnish instances of the relations 
 mentioned : 
 
 OXIDES 
 
 OF IRON 
 
 . 
 
 OXIDES OF MANGANESE. 
 
 
 Iron. 
 
 Oxygen. 
 
 Manganese. 
 
 Oxygen. 
 
 Protoxide 
 
 28 ... 
 
 8 
 
 Protoxide . 277 . 
 
 .. 8 
 
 Sesquioxide 
 
 56 ... 
 
 24 
 
 Sesquioxide 55-4 . 
 
 .. 24 
 
 Ferric acid . 
 
 28 ... 
 
 24 
 
 Peroxide . 27-7 . 
 
 .. 16 
 
 
 
 
 Manganic acid 27-7 . 
 
 .. 24 
 
 
 
 
 Hypermangan- 
 
 
 
 
 
 ic acid . 55.4 . 
 
 . . 56 
 
 The third law is of the utmost importance. If a 
 substance be taken whose range of affinity is very 
 great, and the proportion in which it unites with a 
 number of other bodies accurately determined by ex- 
 periment, a series of numbers will be obtained which 
 represent the relative capacities of saturation of the 
 bodies concerned. For example : oxygen is a sub- 
 stance amply fulfilling the conditions required; it 
 forms a vast number of combinations, for the most 
 part easy to examine. It is found, on trial, that a 
 
APPENDIX. 155 
 
 constant quantity of oxygen say eight parts, by 
 weight enters I into definite chemical union with 
 the other elementary bodies, in such a way as to re- 
 quire of the latter quantities represented by the num- 
 bers below, or by numbers bearing a simple relation 
 to tfiem. 
 
 Oxygen 8 unites with 
 
 Hydrogen ...... 1 
 
 Carbon 6 
 
 Sulphur ....... 16-1 
 
 Chlorine . . ,, , , r . 35-5 
 
 Iodine . . Y Y . . . . 126-3 
 
 Potassium ...... 39-2 
 
 Sodium 23-3 
 
 Iron . . . .j;iu>* . . 28- 
 
 Copper .'..''/. . . 31-6 
 
 Silver . ., . , . . . .. 108- 
 
 Lead . . Y V* .'". . . 103-6 
 &c. &c. 
 
 The numbers thus obtained are termed " equiva- 
 lent," for the very obvious reason that they are the 
 representatives of quantities of matter capable of 
 exactly replacing each other in combination. 
 
 The formation of such lists of chemical equiva- 
 lents is effected by analysis, by experiment alone ; 
 the choice of the substance with which to start, and 
 the quantity of that substance assumed, are alike 
 arbitrary, and are determined by considerations of 
 convenience. 
 
 The great point, the essence of the law under 
 discussion, now follows : it states, that these equiv- 
 alent numbers not only represent the relative pro- 
 portions in which the bodies unite with a given 
 
156 APPENDIX. 
 
 quantity of the substance at the head of the column, 
 but also the proportions in which they unite among 
 themselves whenever combination occurs. 
 
 Thus, in the case cited, when hydrogen and 
 iodine combine, it is in the ratio of 1 to 126-3 ; 
 when iron and iodine unite together, we have J2S 
 parts of the former to 126-3 parts of the latter; 23-3 
 parts sodium, or 39-2 parts potassium combine 
 with 35-5 parts chlorine, or 126-3 parts iodine, or 
 16- 1 parts sulphur, &c. &c. It is impossible to over- 
 estimate the importance of this law, when followed 
 into its consequences. 
 
 The fourth law is also quite independent of the 
 rest, and is also based upon purely experimental 
 proof. 
 
 No reason can be assigned beforehand, that the 
 combining number of the compound body shall be 
 exactly the sum of the combining numbers of its 
 components. The assumed equivalent of sulphuric 
 acid is 40- 1, being made up of one equivalent of 
 sulphur and three equivalents of oxygen. Now, on 
 trying how much potash or soda these 40*1 parts of 
 sulphuric acid will saturate, it is found that of the 
 first 47-2 parts, and of the second 31-3 parts are re- 
 quired to form a neutral combination; but these 
 numbers respectively contain the equivalents of po- 
 tassium and sodium added to that of oxygen, or, in 
 other words, the equivalents of the compounds are 
 made up of the equivalents of their constituents. 
 
 Apart from purely hypothetical considerations, 
 no 'possible reason can be given why 40- 1 parts of 
 acid should exactly require for neutralization the 
 
APPENDIX. 157 
 
 quantities of base mentioned. It is found by experi- 
 ment to do so ; but it was a result that, however it 
 might have been guessed at, could not have been 
 foreseen. 
 
 Among these four separate and independent laws, 
 which, be it ever remembered, rest entirely upon ex- 
 perimental proof, and are altogether unconnected 
 with theory or hypothesis of any kind, relations 
 may be traced important and interesting in the high- 
 est degree. It is to the peculiar nature of these re- 
 lations, and of the laws which they thus link togeth- 
 er, that we must attribute the wonderful facility with 
 which combinations of all kinds are produced, each 
 definite and invariable in its nature, and also the ease 
 with which we are enabled to push our investiga- 
 tions in this department of science ; they furnish us 
 with checks and methods of control which are per- 
 fectly invaluable, and aid to reduce within exceed- 
 ingly narrow limits the inevitable errors of experi- 
 mental inquiry. 
 
 (6.) A very curious relation is found also to ex- 
 ist between the combining quantity of a substance, 
 and its volume, or measure, in the gaseous state. 
 We find that 
 
 8 grains of oxygen, at 60 F. and 30 
 
 inches %ar., occupy .... 23-5 cubic inches. 
 
 1 hydrogen 46-8 
 
 35.5 chlorine 46-5 
 
 126-3 iodine vapour . v ,,;- , 46-7 
 
 It is easy to make this calculation from a know- 
 ledge of the specific gravities of the bodies. 
 
 Now, on examining the second column in the 
 8 
 
158 APPENDIX. 
 
 above table, it will be seen that the last three num- 
 bers coincide so closely that they may be taken as 
 identical, and that the first is as nearly one-half. 
 But the weights are very different indeed they are 
 very remarkable they are no. other than the equiv- 
 alent numbers. 
 
 We have in these peculiar relations of density a 
 most beautiful explanation of the fact, discovered 
 many years since by M. Gay-Lussac,that when gas- 
 eous bodies combine it is always either in equal vol- 
 umes, or in volumes bearing to each other a simple 
 relation ; and it is easy to see why it must be so. 
 Equal measures of chlorine and hydrogen, for exam- 
 ple, combine to form hydrochloric acid gas ; these 
 equal measures contain quantities of matter in the 
 proportion, by weight, of 35-5 to l,or in the ratio of 
 the equivalent numbers. A volume of oxygen unites 
 with two volumes of hydrogen, because these quan- 
 tities are to each other, by weight, in the relation of 
 8 to J. This rule extends to compounds of every 
 description as well as to elementary bodies, and in- 
 deed embraces every substance capable of existing 
 in the gaseous condition. 
 
 It is difficult to avoid the conclusion, that these 
 exquisitely beautiful laws and relations have been 
 framed and adjusted to each other b^an intelligent 
 mind. 
 
 THE END. 
 
 J. F. TROW & Co., PRINTERS, 
 33 Ann-Street. 
 


 UNIV 
 
 UNIVERSITY OF CALIFORNIA I.IBR RY