have led them to anticipate. The case is the same with regard to products first secreted and then excreted, as bile, saliva, etc., which offer a still greater complication. The chemists make no incpiiry about the parts from which these products are taken, or the modifications which may have been occasioned by their remaining some time after their 378 POSITIVE PHILOSOPHY.
production, etc.; and therefore the analyses of these pro- ducts, however often renewed, are still incoherent and thoroughly defective. We owe to M. Raspail a full expo- sure of the practice of the chemists of multiplying oi'ganic principles almost without limit, from differences of character which imply no distinction of nature, but are merely marks of various degrees of elaboration of the same principle in different developments of vegetation; and even from con- founding the observed substances with their anatomical envelope. It is to be regretted that M. Easj^ail did not complete his great service to science by founding rationally the physiological portion of organic chemistry, instead of vainly attempting to systematize organic chemistry, under the bias of our crude chemical education. rp pj.• 1 „, If we turn from the anatomical order of ''" ' questions to the jDhysiological, we shall find yet stronger evidences of the inaptitude of chemists for biological inquiries. All endeavours have yet failed to establish any point of general doctrine in biology; and we find ourselves merely with simple materials, which must be newly elaborated by physiologists, under the view of vitality, before they can be put to use. To give an example or two: — the experiments of Priestley, Sennebier, Saussure, and others, on the mutual chemical action of vegetables and atmospheric air, were of the highest value, as insti- tuting positive knowledge of the vegetable economy; but the inquiry is by no means so simple as its founders natu- rally supposed, after having analysed one separate portion of the phenomenon of vegetation. The absor2:)tion of car- bonic acid, and the exhalation of oxygen, though very important in relation to the action of leaves, are only one aspect of the double vital motion, and cannot be understood but in the physiological view of both. This action cannot explain the elementary composition of vegetable substances, or determine the kind of alteration sustained by the air through vegetation, because it is, in other ways, partially compensated by the precisely inverse action produced by the germination of seeds, the ripening of friiits, etc., and even, as regards the leaves, by the mere passages from light to darkness. It is much to have indicated the true nature of the requisite research, and to have supplied some RELATION TO PHYSIOLOGY. 379 materials for it. The rest is the business of the the physio- logists. If we turn to animal physiology for examples, the case is yet more striking.
After all the inquiry that has been made into the chemi- cal phenomena of respiration, no fixed point is yet estab- lished. It was long supposed that the absorption by the lungs of atmospheric oxygen, and its transformation into carbonic acid, would exj^lain the great phenomenon of the conversion of venous into arterial blood. But the problem is much more complicated than was supposed by the chemists who established this essential part of the phe- nomenon, and whose labours present the most contra- dictory conclusions in regard to the facts under their notice. We do not know, for instance, whether the quantity of carbonic acid formed really corresponds to the quantity of oxygen absoi'bed; and even the simple general difference between the inhaled and exhaled air, which is the first point to be ascertained, is far from being positively estab- lished. The atmospheric azote appears to some to be in- creased after respii*ation, while others say it is diminished, and others again that it remains the same. The disagree- ments about the changes in the composition of the blood are yet more marked. Perhaps the inaptitude of chemists and physicists for physiological researches is more striking still in the case of animal heat. In the early days of modern chemistry, this phenomenon seemed to be suffi- ciently accounted for by the disengagement of heat corre- sponding to the decarbonizing of the blood in the lungs, which the chemists regarded as the focus of a real combus- tion; but this explanation was soon found to be inadequate, even in a normal condition; and much more in various pathological cases. Uncertain as we still are as to the pulmonary influence in the process, we know that all the vital functions must concur in it, in a greater or smaller degree. There is even some reason to suppose, in direct opposition to the opinion of the chemists, that respiration, far from aiding to produce animal heat, con- stantly tends to diminish it. No doubt, the chemical effects occasioned by vital action must always be taken into the account in the study of animal heat; but it is only the physiologists who can deal with them in the light of the 380 POSITIVE PHILOSOPHY.
whole subject. When we have learned to combine the chemical and the physiological view, we may proceed to the tormation of positive doctrine, without having to deal with preliminary obstacles; as, in regard to such questions as the general agreement between the chemical composition of living bodies, and that of the whole of their aliments; a case which constitutes one of the principal aspects of the vital state.
It is evident, at the outset, that every living body, what- ever its origin, must be, in the long run, composed of the different chemical elements concerned in the substances, solid, liquid, and gaseous, by which it is habitually nourished; since, on the one hand, the vital motion sub- jects its parts to a continual renovation, and, on the other, we cannot without absurdity sujjpose it capable of spon- taneously producing any real element. This consideration is so tar irom involving any difficulty, that it might lead us to divine the general nature of the principal elements of living bodies; for animals feed in the first place on vegetables, or on other animals which have eaten vege- tables; and in the second place, on air and water, which are the basis of the nutrition of plants: and thus, the organic world evidently admits of those chemical elements only which are furnished by the decomposition of air and water. When these two fluids have been duly analysed, physiologists can, in a manner, forsee that animal and vegetable substances must be composed of oxygen, hydro- gen, azote, and carbon, as chemistry taught them. It is true, such a prevision must be very imperfect, as it indicates nothing of the difference between animal and vegetable substances, nor why the latter usually contain so much carbon and so little azote. But this hrst glimpse, though it suggests some of the difficulty of the problem, yet indi- cates the possibility of establishing such a general harmony. But, when we proceed with the comparison, we encounter important objections, which are at present insoluble. The chief difficulty is that azote appears to be as abundant in the tissues of herbivorous as of carnivorous animals, though the solid aliments of the former contain scarcely any azote. The opinions of chemists, as of J>erzelius and Kaspail, as to the nature of azote, do not solve the difficulty, as they DIVISIONS OF ORGANIC CHEMISTRY. 381 cast no light upon its origin. This is one of a mnltitnclp of cases in which we cannot at all explain the chemical composition of anatomical elements bv that of the exterior substances from which they are iniqnestionably derived. Another striking case is that of the constant presence of carbonate, and, yet more, phosphate of lime in the bonv tissue, though the nature of the aggregate of aliments appears to afford no room for the formation of those salts. This system of investigations, considered in its whole range, constitutes one of the most important general ques- tions that can arise from the chemical study of life; and, if it is at present hardly initiated, the backwardness is owing, not only to its eminent difficulty, but to the bio- logists having abandoned to the chemists a task which. UTider a wise organization of labour, would have belonged to themselves alone.
In order to effect a rational division of Partition of organic chemistry, and to assign its ]>ortions Oi-o-anic to chemistry on the one hand and physiology Chemistry. on the other, we must talce our stand on the separation between the state of life and that of death; or. what comes to nearly the same thing, between the stability and in- stability of the proposed combinations, submitted to the influence of common agents. Among the compounds in- discriminately called organic, some owe their existence only to vital motion; they exhibit perpetual variations, and usually constitute mere mixtures: and these cannot belong to chemistry, but must enter into the domain of biologv, — statical or dynamical, according as we study their fixed condition, or the vital succession of their regular changes. Such, for instance, are l)lood, lymph, fat. etc. The others, which form the more immediate principles of these, are substances essentially dead, admitting of a remarkable permanence, and presenting all the characters of true com- binations, independent of life: their natural pla.ce i" evidently, in the general system of chemical science, among the substances of inorganic origin, from which they differ in no important respect. Of these, the organic acids, alcohol, albumen, etc., are examples. These are the sub- stances which truly belong to organic chemistry; and no reason exists for their separation from analogous inorganic 382 POSITIVE PHILOSOPHY.
substances, eveu if no injury was done by sucb an arbitrary division; and there is more reason for giving the title of organic to them than to the theory of oxygen, hydrogen, carbon, and azote, or to the study of many other substances, acid, alkaline, saline, etc., without which chemical anatomy and physiology would be unintelligible. As for chemical phenomena truly common to all compounds of this class, in consequence of the necessary identity of their chief elements, it is certainly important to assign to them their precise relations. The most important of these phenomena relate, at present, to the interesting and very imperfect theory of the diiferent kinds of fermentation. But the consideration of these properties does not constitute a different order from that which results from the same ground in the case of many other comj)ounds, purely in- organic. The property of fermentation, however important, has not a higher scientific value than that of burning, and has no more right to an exclusive classification. It is admitted that too much was attributed to combustion formerly, in regard to inorganic substances; and we may be attributing too much now to fermentation, or any other common property, among so-called organic bodies. We cannot yet assign their proper place to these compounds in the rational system of chemical science; but we are able to affirm that, in that system, they must be more or less sej)arated from each otlier, and interposed among sub- stances called inorganic. Nothing more than this is needed to settle the question of the maintenance or the suppression of organic chemistry as a distinct body of doctrine. In applying the principle which I have proposed, to ascer- tain to which science any question belongs, it is enough to inquire whether chemical knowledge will serve the pur- poses of the research, or whether any biological considera- tions enter into it. The i^roposing such an alternative is, in fact, making the classification.
It is not our business to treat of any special application of this principle; but it is desirable to point out that in this partition of organic chemistry, its two portions are very unequally divided — the study of vegetable substances contributing most to chemistry, and that of animal sub- stances to biology. At the first glance, we might suppose APPLICATION OF DUALISM TO ORGANIC COMPOUNDS. 383 the difference to be the other way; for the iraportance of chemical considerations is really much greater with regard to living vegetables than animals, whose chemical functions are, except among the lowest orders of the zoological hierarchy, subordinated to a superior order of new vital actions. Yet, in virtue of the higher degree of vital elabo- ration that matter undergoes in the animal than in the vegetable organism, the chemical part of animal physio- logy j)resents a much greater extent and complexity than the vegetable, in which, for instance, the whole series of the phenomena of digestion is absent, and in which assimi- lation and secretion are much simplitiecl. But, on account of the superior elaboration, and of the greater number of elements, animal substances are much less stable than vegetable: they rarely remain separate from the organism; and, at the same time, the new immediate principles proj)er to them are so few that their very existence has been ques- tioned. Vegetation is evidently the chief source of true organic compounds, which are derived thence by the animal organism, and modified by it, either thi'ough their mutual combinations or new external influences. Thus, the true domain of chemical science must necessarily be more extended by the study of vegetable than by that of animal substances.
Enovigh has been said about the necessity of subjecting organic compounds to the law of dualism; but there is a particular aspect, under which the importance of this conception in improving chemical theories is worth a brief notice.
In considering substances as ternary or Application of Cjuaternary, their multiplicity is accounted dualism to for only bv the difference in the proportions organic of their constituent elements,— their com- compounds, ponent principles being identical. Very great differences are sometimes explained by inequalities of proportion so small as to shock the spirit of chemical analysis: and in other cases, the proportions being the same, the differences remain unaccounted for; — as, for instance, in the cases of sugar and gum, in which we find the same elements, com- bined in the same ^proportions. If we extend dualism to organic compounds, this class of anomalies disapj^ears; 384 POSITIVE PHILOSOPHY.
for the distinction betAveeu immediate and elementary analj^sis enables us to resolve bv dualism, in the most natural manner, the s^eneral paradox of the real diversity of two substances composed of the same elements, in the same projiortions. In fact, these substances, identical in their elementary, would differ in the immediate analysis, as Ave may understand from what was offered in my chapter on the law of definite proportions. In another connection, chemists have remarked the possibility of exactly representing^ the numerical composition of alcohol or ether, etc., according to several binary formulas, radi- cally distinct from each other, and yet finally equivalent with regard to the elementary analysis. Now, if svich fictitious combinations should ever be realized, they would prodvice highly distinct substances, which might differ much in the aggregate of their chemical properties, and yet coincide by their elementary composition. It is only necessary to transfer the same spirit into the study of organic combinations, by the establishment of a universal dualism, to dissipate all these anomalies: and the re- soui'ce may thus be happily pre])ared, before the cases of isomerism (as Berzelius calls this fact) have become very numerous.
We have now seen how heterogeneous is the"char)ter ^^^^ body of doctrine included under the name of organic chemistry; how it should be divided; what is the duty of physiologists with regard to their share of it; and how the extension of dualism will establish a natural agreement between the composition of substances and their collective characters.
With regard to Chemistry at large, I have tlie^Boolf *^ pointed out the true spirit of the science, under a philosophical view of its present aspects, and of the indispensable conditions of its advance- ment. We do not want new materials so much as the rational disposition of the details which already abound: and I have offered two prominent ideas, in my survey of chemical philosophy; the fusion of all genuinely chemical studies into one body of homogeneous doctrine; and the reduction of all combinations to the indispensable concep- tion of a dualism always optional. These two conditions, SUMMARY. 385 SUMMARY. 385 distinct but connected, have been presented as necessary to the definitive constitution of chemical science. The application of such a conception to the only part of chemical research which yet exhibits anything of a posi- tive rationality has removed all doubt about its general fitness, by showing its spontaneous aptitude to resolve the anomalies of numerical chemistry.
With this division closes our survey of the whole of natural philosophy that relates to universal or inorganic phenomena. In the order of phenomena to which we next proceed, there is at once much more complexity, and much less established order. The study of them is scarcely yet organized; and yet, out of the speciality of the pheno- mena arises the most indispensable part of natural philo- sophy,— that of which Man is first the chief object, and then Society.
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