352 VETERINARY PHYSIOLOGY 



The process is one of breaking down a complex molecule 

 into simpler molecules, probably with hydration. 



The object of this was formerly supposed to be to allow of 

 the diffusion of the protein in the form of peptone through the 

 wall of the intestine. It is now known that absorption is not 

 due to diffusion, and it is more probable that the change to 

 the simplest protein molecule is a step to the more complete 

 disintegration of the molecule which seems necessary before 

 it can be built into the special protoplasm of the body of the 

 particular animal. 



On certain proteins and their derivatives the gastric juice 

 has a special action. On collagen the HC1 acts slightly in 

 converting it to gelatin. The gastric juice acts on gelatin, 

 converting it to a gelatin peptone. 



On nucleo-proteins it acts by digesting the protein part and 

 leaving the nuclein undissolved. 



Haemoglobin is broken down into hsematin and globin, and 

 the latter is changed into peptone. 



The caseinogen calcium compound of milk is first coagulated 

 and then changed to peptone. The coagulation is brought 

 about by the presence of the second enzyme of the gastric 

 juice rennin. 



This may be separated from pepsin in various ways, and, 

 unlike pepsin, it acts in a neutral medium. 



The change set up by it seems to be due to a splitting of 

 the soluble calcic compound of caseinogen which exists in milk 

 into calcic paracasein, which is insoluble and is thrown down, 

 and a small quantity of wbey albumin which remains in 

 solution. The nuclein part of the paracasein remains undigested. 



The gastric juice contains an enzyme which splits Fats into 

 fatty acids and glycerine if they are in a very fine state of sub- 

 division, as in milk, but it has no action on fats not so sub- 

 divided. When fats are contained in the protoplasm of cells, 

 they are set free by the digestion of the protein covering. 



On Carbohydrates the free mineral acid of the gastric juice 

 has a slight action at the body temperature, splitting the 

 polysaccharids and disaccharids into monosaccharids. 



(c) Digestion of the Stomach Wall. When the wall of the 

 stomach dies either in whole, as after the death of the animal, 



