24S DIGESTION AND ASSIMILATION OF THE FOODSTUFFS 



tion in the form of the further cleavage-products, the Peptones. The 

 following are typical results obtained: 



Percentage of proteoses 



Protein in on completion of 



the diet. gastric digestion. 



Egg-albumin 72.5 



Gliadin 67.7 



Edestin 60.3 



Casein 59.1 



Gelatin 50.6 



Serum-albumin 46 . 1 



the remainder of the protein having reached the peptone-stage of 

 cleavage. With varying quantities . of the same protein a definite 

 proportion of proteoses is always formed, as the following results 

 illustrate: 



Quantity of fdiadin Percentage of proteoses 



in a meal. on completion of 



Grams. gastric digestion. 



25 80.8 



50 86.1 



75 . . 86.5 



100 84.9 



The significance of gastric digestion lies in the preparatory work 

 which it accomplishes for the intestinal and pancreatic enzymes. 

 The hydrolysis of proteins by Trypsin is much more rapid and complete 

 if the protein has been subjected to preliminary digestion by pepsin, 

 and the hydrolysis of proteins to the peptone and proteose stage, 

 furthermore, converts the protein foodstuffs into forms open to attack 

 by the Erepsin in the succus entericus. The superior velocity and 

 thoroughness of intestinal protein digestion to the digestion of pro- 

 tein in vitro by pancreatic trypsin is attributable in large measure 

 to the fact that the various proteolytic enzymes act in conjunction 

 or succession upon the protein foodstuffs in the alimentary canal, and 

 also to the fact that the products of digestion are removed almost as 

 rapidly as they are formed. 



In addition to the conversion of proteins into proteoses and peptones, 

 the gastric juice has the special property of converting the casein of 

 milk into Paracasein. 1 Paracasein has recently been shown to be 

 derived from casein by partial hydrolytic cleavage, the paracasein 

 molecule representing one-half the casein molecule. Paracasein 

 resembles casein very closely in its general properties and behavior, 

 but its calcium salt is rendered insoluble by a very slight excess of 

 calcium ions at a much lower temperature than the corresponding salt 

 of casein itself. If a sufficiency of calcium chloride, for example, 

 be added to a solution of calcium caseinate, the protein salt will be 



1 In British scientific literature these substances are termed, respectively, Caseinogen 

 and Casein. The word casein, therefore, means the unmodified protein of milk, in 

 American literature, and the infraprotein derived therefrom by the action of Rennin, 

 in British literature. The American nomenclature is to be preferred because it possesses 

 the claim of priority, and is that generally employed in other languages. 



