CHAPTER XII 



THE PARENTERAL INTRODUCTION 

 OF PROTEINS 1 



FOR a long time it was thought that the proteins of our 

 food undergo but slight modification before absorption 

 through the walls of the alimentary canal. The studies 

 of Beaumont laid the foundation of the scientific investi- 

 gation of proteolytic digestion, and soon it was shown that 

 the digestive juices convert proteins into peptones. 



After experiments had demonstrated that peptone is 

 formed in alimentary digestion and had shown the com- 

 paratively ready diffusibility of the digestive products, 

 several questions arose. Among these may be mentioned 

 the following: (1) Is all the protein converted into peptone 

 in the alimentary canal, or is part of it absorbed in unaltered 

 form? (2) What is the fate of peptone after absorption? 



Briicke, 2 whose studies on pepsin and its action made him 

 one of authority in this matter, held that only a part of 

 the protein is converted into peptone in alimentary diges- 

 tion, and that much of the soluble protein of the food is 

 absorbed unchanged. Furthermore, he taught that the 

 fate of the two after absorption is different. The peptone, 

 he taught, is rapidly oxidized and serves as a source of 

 energy, but is not utilizable in the building of tissue, the 

 latter function devolving solely on the protein absorbed in 

 unaltered form. Briicke's arguments in support of this 

 theory may be briefly stated as follows: 



1 This is largely taken from an article by Vaughan, Gumming, and 

 McGlumphy (Zeitsch. f. Immunitatsforschung, 1911, ix, 16). 



2 Sitzungsber. d. k. Akad. d. Wissensch. zu Wien, 1859, Band xxxvii, 

 ibid., Band lix. 



