210 METAMORPHOSIS OF TISSUE. 



correct one which derives a new substance from the original one 

 by the mere substitution of individual elements. There is one 

 circumstance, however, which appears, at all events, to prove that 

 the simplest chemical equation is not always the most correct in 

 these processes, which seem to depend upon such highly compli- 

 cated conditions. For, when we find that a concurrence of many 

 different substances is necessary to the accomplishment of many 

 processes, as, for instance, that nutrient matters are only imper- 

 fectly, if at all, digested without the presence of fat, that no cell, 

 fibre, or membrane can be formed without the presence of fat, 

 phosphates, &c., we can scarcely suppose that a simple formula, 

 based upon an unestablished atomic composition can express the 

 true process of the metamorphosis. There are certain substances 

 which never occur isolated in the animal organism during chemical 

 metamorphoses ; thus, for instance, wherever albuminous matters 

 occur, non- nitrogenous carbo-hydrates are always present, how- 

 ever small may be their amount ; wherever fats are formed or 

 decomposed we always meet with albuminous matters ; whilst free 

 acids and alkalies occur in almost every part of the animal body. 

 Although we may not admit the necessity of the concurrence of 

 two or more entirely different substances in the case of individual 

 processes, we rather conjecture that such a necessity obtains from 

 the analogy of those processes which we are able to induce in 

 organic substances that are not included in the sphere of vitality. 

 We perceive very clearly from a study of the process of fermentation, 

 that one organic substance cannot exist together with another 

 undergoing the process of metamorphosis, without being implicated 

 in an analogous molecular motion, corresponding to its constitution. 

 May we not conjecture that the substances formed under these 

 conditions possess the tendency to combine together in their 

 nascent state, and thus give occasion to the formation of certain 

 complex atoms, in which chemistry has recognised proximate 

 constituents, conjugated compounds, haloid salts, &c. ? It is 

 here that the recent chemical theory of the substitution of 

 certain elements by other more simple or compound molecules 

 will find the most extended application, and where we shall dis- 

 cover new proofs of the generally recognised proposition, that 

 nature, under all circumstances, accomplishes the most varied ends 

 by the simplest means. Hence it would be difficult to prove, 

 and indeed it appears almost improbable, that those nitrogenous 

 matters which have less affinity with albumen, as for instance, the 

 animal pigments, the resinous acids of the bile, &c., are the simple 



