192 DIGESTION 



sorts of proteoses follow this as successive cleavage-products before the 

 mass becomes peptone or polypeptids. The polypeptids are as yet 

 ill-defined component parts apparently of peptones. These have already 

 been synthesized artificially from their constituents; perhaps proteids 

 themselves will be made before long. (See below.) Kuhne and Neu- 

 meister suppose that two proteoses intervene between the syntonin and 

 peptone called primary and secondary proteoses respectively. Pick 

 finds reason to believe that there are four of these. In the great un- 

 certainty attending the details of peptic hydrolysis at present it is almost 

 useless to study the often contradictory theories of the matter farther. 

 It is almost enough to suppose that the pepsin and acid (or the latter 

 alone?) produce successively syntonin, then two or more proteoses, 

 then one or more peptones, and possibly even amido-acids, each substance 

 having a simpler and probably smaller molecule than its immediate 

 predecessor. In schematic and probably incomplete form : 



Proteid. 



Syntonin. 



Proto-proteose. 



Deutero-proteose . 



Ampho-peptone. 



In this schema the "ampho" of the peptone implies the probable presence 

 of two sorts of peptone, sometimes called hemi-peptones and anti- 

 peptones respectively. Simpler than the peptones are substances, 

 polypeptids, found by Pfaundler, E. Fischer, Salaskin, etc., which are 

 probably combinations of amido-acids for example, leucinimide. The 

 molecular weights of these and simpler decomposition-products of peptic 

 hydrolysis are probably not over 5 per cent, of thf i of the proteid with 

 which the digestive process started. These obviously are, therefore, 

 much more suitable materials for tissue-building than more complex 

 and unstable substances. For the body-protoplasm to try to build 

 protoplasmic tissue out of proteids, or peptones even, were much as if 

 a contractor should attempt to make a satisfactory brick house out of 

 second-hand bricks which had not been taken apart and cleaned, but used 

 rather in the large masses in which the former walls had fallen. In the 

 case of digestion by acid and pepsin it is still in doubt just how complete 

 the separation and renovation of the proteid-materials are. There is 

 some evidence (Mann) that the peptic process is one of aiding the dis- 

 integrating powers of the hydrogen and hydroxyl ions in the epithelium. 

 "Rennin" is the second of the enzymes so far isolated from the secre- 

 tion-product of the stomach. It may be but an aspect of pepsin. Its 

 function if a separate enzyme is to coagulate milk and to do probably 

 other things not yet determined, for it is secreted by the stomachs of both 

 birds and fishes, to which of course milk is for the most part quite 

 unknown. Like pepsin, rennin acts only in an acid medium. As has 



