ANIMAL OXIDATIONS. 443 



the cleavage-products of this substance. To be sure, this does not explain 

 why the nascent oxygen set free in the combustion of other foodstuffs, 

 is not able to act upon d-glucose. At all events, the assumption that oxi- 

 dation is preceded by a hydrolysis, gives to the cell the power of utilizing 

 its nutriment at the time it is needed. We know that the action of the 

 ferments is specific, i.e., that they are able to act only upon certain definite 

 compounds. If it be assumed that the cells do not contain the ferment 

 in an active condition, but that the ferment is activated only when its 

 action is needed, we are able to understand very clearly much about the 

 economy of the cells. We begin to understand how the cell can have 

 the food, the ferment, and oxygen all present together without any com- 

 bustion taking place, until at a given moment the ferment becomes 

 activated. The following phenomenon harmonizes well with such an 

 assumption. 



The animal organism consumes without difficulty the cleavage-products 

 of the food which it obtains as such. Thus the decomposition products of 

 albumin, such as glycocoll, alanine, etc., are readily oxidized to urea. 1 This 

 is true, however, only of those amino acids which are present in albumin, 

 i.e., those having the same configuration. If, for example, instead of feed- 

 ing a rabbit with Z-leucine, we administer the racemic form, d-Z-leucine, 

 only a part of the molecule, namely the Z-leucine, is oxidized, while the 

 other half of the racemic substance molecule, the right-rotating leucine, 

 appears unchanged in the urine. This is evidently because the animal 

 cells are not adapted to the combustion of d-leucine, which under ordinary 

 conditions is foreign to it, so that it possesses no ferment to attack it. 

 The oxygen, therefore, is not able to attack it. Furthermore, it is not 

 strange that when the combustion is very vigorous a part of this substance 

 is actually oxidized. We may indeed assume that oxygen activated by 

 some other decomposition process can cause such oxidation. 



Interesting as this hypothesis appears, we must not forget to state that 

 in this simple form it does not suffice to explain all the phenomena pertain- 

 ing to animal oxidation. The actual relations are far more complicated 

 than we have indicated. Above all, we would expect that in the absence 

 of oxygen there would tend to be a piling-up of these readily oxidizable sub- 

 stances, and to a considerable degree, particularly as now the entire energy 

 required by the organism must be furnished by the hydrolytic decomposi- 

 tions. We have already mentioned experiments performed in this direc- 

 tion. 2 G. von Bunge 3 has shown that ascarids are able to exist, for 

 several days without any oxygen supply. During this time they move 

 about quite actively. The energy necessary in such cases must be pro- 



1 Cf. Lecture XI, p. 228. 



2 Lecture IV, p. 74. 



3 Z. physio] . Chem. 14, 318 (1890). 



