STOMACH AND INTESTINE. 



383 



another organization of yesterday ; that its 

 individual descent from two creatures of the 

 same species is accompanied by a less evident, 

 but quite as real, transmission of substance 

 from several previous beings. In short, that 

 the greater part of its entire mass might be 

 regarded as the sum of various legacies, whieh 

 have been bequeathed to the existing organism 

 by the various plants and animals that lived 

 before it. 



In the next place, it indicates a fixed and 

 definite relation between the plant and the 

 animal. The former is thus the chief agent 

 in the constructive chemistry of the latter : 

 a necessary link in that chain of processes 

 which builds up organic principles, out of the 

 elements of inorganic nature, or out of those 

 simple products into which the particles of the 

 animal body are finally converted by its waste 

 during life, or its putrefaction after death. 

 The carbonic acid given off by the living 

 or dead animal may especially exemplify the 

 latter remark ; converted as it is, by the 

 vegetable, from a poisonous gas into a class 

 of substances which are in the highest sense 

 alimentary, and essential to the life of the 

 animal. 



And lastly, since animal and vegetable life 

 are thus complementary to each other, alike 

 in their broader features and their minuter 

 details, we may conjecture that, in the 

 present disposition of our planet, they form 

 what is in fact a tolerably constant magni- 

 tude : a sum of organized life, the amount 

 of which is subject to but very slight varia- 

 tion from one time to another. Nay more, 

 we may almost suspect that the total of 

 animal existence the composition of which 

 ranges thus regularly through vegetable or- 

 ganization as an essential part of its cycle 

 of metamorphosis is in the main equally 

 constant and fixed. Created by what even 

 modern science must be content to own as a 

 miracle, in the strictest sense of the word, it 

 seems not improbable that animal, as well as 

 vegetable life, is sustained in consonance with 

 some vast law of this kind. According to 

 such a law, each by each, and both together, 

 would make up certain constant units ; the 

 innumerable constituent fractions of which 

 might vary within vast limits without ex- 

 ercising any effect on their respective sums. 

 And thus the world of life around us would 

 but parallel that perpetual flux, but un- 

 altered quantity, which the chemist has long 

 predicated of the various materials which 

 compose the inorganic globe we inhabit. 



But if, on the one hand, the animal is in- 

 capable of constructing its complex tissues 

 from the simple elements of inorganic nature, 

 still, on the other hand, it is not bound down 

 by such rigorous chemical necessities, as to 

 demand a food possessing an exact identity 

 of composition with itself. A large propor- 

 tion of the animal creation feed on a vegetable 

 diet, the constituents of which deviate con- 

 siderably from those of their own mass. And 

 but very few of even the more carnivorous 

 animals are in the habit of devouring their own 



species. Finally, though the blood forms the 

 pabulum of all the tissues, and hence closely 

 approaches their total composition, still it 

 does not appear to form even an advantageous 

 article of food, far less an indispensable one. 



And while such considerations may suf- 

 fice to show, that there is no true identity be- 

 tween the food and the tissues in general, the 

 progress of modern physiological chemistry 

 plainly indicates, that an identity of this kind 

 would be equally impossible in detail. Tims 

 it is not improbable, that the tissues of every 

 individual possess chemical peculiarities more 

 or less specific to himself. And it is all but 

 certain, that the various proximate principles 

 isolated by the chemist are not definite com- 

 binations of certain elements in equivalent 

 proportions as are the salts, acids, and alka- 

 lies of the inorganic world but rather ever- 

 varying mixtures. Those various forms of 

 protein which it is so convenient to distinguish 

 by the names of albumen, fibrin, and casein, 

 may indeed be separated from the tissues of 

 animals, and even of vegetables, by the same 

 rough processes ; and may therefore respec- 

 tively exhibit the closest resemblance in their 

 composition and properties. But an accu- 

 rate analysis would probably show, that the 

 organic substance represented by either of 

 these terms is never precisely identical in any 

 two specimens. It is the total of a number of 

 constituents, the result of a variety of pro- 

 cesses, the end of a serial metamorphosis : 

 rather than a definite and specific compound 

 of carbon, oxygen, hydrogen, and nitrogen. 



And not only is there no identity in the 

 composition of the organism and the ingesta, 

 but it would seem that there are some tissues 

 of the body which have absolutely no repre- 

 sentative in the food : no kindred substance to 

 which their formation can possibly be referred. 

 Such are the various tissues that yield gela- 

 tine ; a substance which, though it appears 

 to escape assimilation when introduced into 

 the organism from without, is yet constantly 

 formed within it, from the metamorphoses of 

 other parts of its substance. 



The chemistry of nutrition therefore implies 

 neither construction, on the one hand, nor 

 identity, on the other ; but something mid- 

 way between these two extremes. Its forces 

 occupy, so to speak, a debateable ground 

 between the prehension of old materials, and 

 the formation of new ones. And the food 

 submitted to its action is only required to 

 possess such a similarity of composition with 

 the body, as will concede these limited 

 changes, without implying any wider process 

 of metamorphosis. 



Any exact definition of the degree of re- 

 semblance thus requisite, would be foreign to 

 our present object. Indeed, in the existing 

 state of our knowledge, it is impossible to 

 specify the precise nature of those metamor- 

 phoses, which accompany the digestive act ; 

 and are bounded by the food and the organ- 

 ism as their respective beginning and end. 

 It is enough to indicate, that they appear to 

 be intermediate between the forces of che- 



