38 PRINCIPLES OF ANIMAL NUTRITION. 
detail, represents the two supposed stages in the katabolism of fat 
by the two following equations, proposed by Chauveau:* 
First Stage: 2(C,H,,,0,) +670, = 16(C,H,,0,) + 18CO,+ 14H,0. 
Second Stage: 16(C,H,,0,) +960,=96CO,+96H,O. 
Even, however, if we admit the formation of dextrose from fat 
in the body, it may fairly be doubted whether the process is as 
‘simple as these equations, even if regarded as simply schematic, 
would imply. 
§ 3. Proteid Metabolism. 
ANABOLISM. 
Digestive Cleavage.—The digestion of the proteids is essen- 
tially a process of cleavage and hydration under the influence of 
certain enzyms. By this process the complex proteid molecules 
are partially broken up into simpler ones. By the action of pepsin 
in acid solution we obtain albumoses and peptones, while the 
trypsin of the pancreatic juice, at least outside the body, carries 
the cleavage still further, producing crystalline nitrogenous bodies of 
comparatively simple constitution. Opinions are still more or less 
divided as to how far these processes of cleavage and hydration are 
carried in the actual process of digestion, where the products of the 
action are constantly being resorbed, but there are not wanting in- 
dications that it is both less extensive and less rapid than in arti- 
ficial digestion. It likewise seems to have been demonstrated that 
some soluble proteids are capable of direct resorption without 
change, while others are not and some, notably casein, are promptly 
coagulated by the rennet ferment, apparently expressly in order 
Ahat they may be subjected to the action of the digestive ferments. 
In a general way, the statement appears to be justified that the 
larger share‘of the proteid material of the food is resorbed as 
albumoses and peptones. > 
PURPOSE OF THE CLEAVAGE.—The fact just mentioned that, 
on the one hand, some soluble proteids appear capable of direct re- 
sorption, while, on the other hand, some, like casein, are at once 
rendered insoluble as the first step in digestion, plainly necessitates 
a material modification of the old view that the object of the cleav- 
* La Vie et l’Energie chez 1 Animale. 
