CHEMICAL PEOCESSES IN CELLS. 145 



Just as urea is readily broken up into ammonium carbonate, or 

 NH S and C0 2 , so also formic and oxalic acids, the terminals of the non- 

 nitrogenous organic molecules, readily undergo decomposition into 

 C0 2 and H a O. 



It cannot be pretended that we are familiar with all the intermediary 

 stages of these retrogressive metamorphoses, yet we are possessed of 

 numerous facts, gained through the study of the decomposition of albu- 

 men by various chemical agents, which go far to fix the character of 

 these changes. Thus, in the artificial decomposition of albumen by 

 certain chemical reagents, asparagin, glutanimic acid, leucin, and tyrosin 

 are constantly met with ; and since these bodies occur in the process of 

 germination in seeds, and the latter two often in the animal body at the 

 seat of rapid break down of albuminoid matter, we may infer that a simi- 

 lar process normally occurs in animal cells. So, also, by various methods 

 of oxidation uric acid is readily converted outside of the body into urea, 

 allantoin, oxalic acid, and carbon dioxide; and there are many facts for 

 supposing that a similar conversion occurs in the animal body. Thus, the 

 administration of uric acid produces not an increase in the uric acid 

 eliminated, but in the urea and calcium oxalate ; and since uric acid is 

 normally present in but small amount in the urine of the carnivora, and 

 is absent in that of the herbivora, while we know that in certain organs 

 of both classes of animals it is formed in considerable amount, it must 

 undergo oxidation in the economy. This is further proved by the fact 

 that a reduction in the supply of oxygen leads to an increase in the uric 

 acid and a decrease of the urea in the urine. In a similar way is to be 

 explained the appearance of allantoin in the urine of cats and dogs when 

 fed on abundant animal diet. 



A similar line of argument may be made to apply to the decompo- 

 sition of the non-nitrogenous tissue-constituents. 



We are thus, to a certain extent, familiar with the starting point and 

 terminals of the series of decompositions which occur in the animal 

 bod}^, and with a few of the intermediary links in this chain. We shall 

 again have to return to this subject in the study of Nutrition. 



3. Fermentations. — The word fermentation is derived from fervere, 

 to boil, and owes its origin to the appearance presented by sugary fluids 

 when placed in contact with ferments ; gas is liberated, the sugar disap- 

 pears, and the product becomes alcoholic. While the term fermentation 

 was originally restricted to this process, it is now applied to many cases 

 in which an organic body when dissolved is modified, changed, and trans- 

 formed under the action of formed or soluble ferments. As regards the 

 action of fermentation only the results and processes of the soluble fer- 

 ments will here demand consideration. 



The soluble ferments act on a large number of organic compounds, 



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