METABOLISM. 41 
formed in the digestive canal and is the form in which the proteids 
of the food are resorbed, and points out that this hypothesis accounts 
for the hitherto puzzling fact of the occurrence of the milk-curdling 
ferment in animals, such as birds, fishes, and amphibia, which never 
consume milk. In further support of this view, Winogradow * 
finds the formation of chymosin in the stomach to be most active 
at the height of the digestive process, when peptones are being 
formed most freely. 
The proteid or proteids first formed from the albumoses and 
peptones, whether in the epithelial cells or by the action of 
chymosin, is subject to still further changes in other portions of the 
body, inasmuch as all the various nitrogenous tissues of the body 
are formed from it. Some of these changes may be slight, but 
others, as, e.g., the formation of the collagens, must be profound, 
while the formation of the compound proteids like hemoglobin, 
mucin, the nucleins, etc., is clearly synthetic and anabolic. As 
to where and how these changes and syntheses take place, we are 
largely ignorant. We simply know the general fact that the food 
proteids are first partially broken down in the process of digestion 
and then that the fragments are built up again into body proteids; 
first, probably, into some single form and later into still more com- 
plex bodies in the various tissues. 
KATABOLISM. 
Final Products.—The anabolic processes which have just been 
indicated might be characterized in general terms as a preparation 
of the food proteids for their diverse functions in the body. In the 
performance of those functions they, like all the organic ingredients 
of the body, undergo katabolic changes, liberating the energy which 
was originally contained in them or which may have been tem- 
porarily added in the preliminary anabolic changes. We have 
every reason to believe that the katabolisth of proteids is a gradual 
process, passing through many intermediate stages, but we have 
very little actual knowledge of the steps which intervene between 
the proteids and bodies which are either excretory products 
themselves or closely related to them. Such information as has 
* Arch. ges. Physiol., 87, 170. 
