326 FOOD AND DIGESTION 



of the new proteid formed. Peptones have certain characteristics which 

 distinguish them from other proteids. They are diffusible, i.e., they possess 

 the property of passing through animal membranes. In their diffusibility 

 peptones differ remarkably from egg albumin, and on this diffusibility depends 

 one of their chief uses. Egg albumin as such, even in a state of solution, would 

 be of little service as food, inasmuch as its diffusibility renders difficult its 

 absorption or in the case of insoluble proteids effectually prevents absorption 

 into the blood-vessels of the digestive canal. When completely changed by 

 the action of the gastric juice into peptones, albuminous matters diffuse readily, 

 and are thus quickly absorbed. 



Peptones are not found in the blood, even of the vessels immediately con- 

 cerned in absorption from the stomach and intestines. In their absorption, 

 therefore, by the epithelial cells, they must undergo a synthetic change, ap- 

 pearing in the blood as albumins and globulins, which are not readily diffu- 

 sible and which occupy the same plane as the proteids from which the peptones 

 were derived. The previous cleavage to proteoses and peptones is in the 

 nature of preparation for this final act of absorption. 



Products at Different Stages of Gastric Digestion. The proteid 

 is first changed into syntonin, or acid proteid, by the combined action of the 

 pepsin and acid. Though the acid alone is capable of accomplishing this 

 step, the fact that it does not do so physiologically is proven by the great length 

 of time required, in laboratory experiments, for the change. 



The next change is the conversion of the syntonin into proteoses which, 

 according to Neumeister, occurs in two successive stages. The first of these 

 stages is the conversion of syntonin into the primary proteoses, i.e., proto- 

 proteose and hetero-proteose. The second is the conversion of both proto- 

 proteose and hetero-proteose into the secondary proteoses, i.e., deutero-proteose. 

 The last change is the conversion of the deutero-proteose into the end product 

 peptone. This last change does not occur completely to any great extent and 

 the proteoses always predominate in the digesting mass. Schematically the 

 changes in the proteids may be represented as follows: , 



Proteid. 



I 

 Syntonin (acid proteid). 



I I 



Proto-proteose. Hetero-proteose. 



I I 



Deutero-proteose Deutero-proteose. 



i I 



Peptone. Peptone. 



The action of pepsin is one of hydrolysis and the products are hydrated 

 forms of proteid. The acid is absolutely essential to the action of pepsin, but 

 it also aids digestion by causing the proteids to absorb water. That this ac- 



