292 DIGESTION 



It is naturally a matter of great interest to determine how the transforma- 

 tion of proteid actually goes on in the stomach; for one can never form any 

 definite conclusion about the cleavages actually taking place in life from 

 experiments in vitro (page 244). Among the more recent contributions to 

 our knowledge of this subject are the researches of Zunz on the digestion of 

 meat in the stomach of the dog. At whatever time between one-half hour 

 and six hours after feeding, the stomach contents were obtained, they con- 

 sisted in by far the greatest part (eighty-six to ninety-eight per cent of the 

 total nitrogen) of albumoses. Acid albumin was present only in small quan- 

 tities and the total quantity of peptones, peptoids and end products only ex- 

 ceptionally reached more than ten per cent of the total nitrogen. Among the 

 latter was found only a very sparing quantity of crystalline products, leucin, 

 tyrosin, etc., and these might have been formed previously in the meat fed. 



These results are to be explained in one of two ways: either the cleavage 

 of proteid in the stomach proceeds only so far that about ten per cent of the 

 proteid-N is transformed into end products, or the end products as they are 

 formed are absorbed more rapidly through the stomach wall than the albu- 

 moses. It is not easily conceivable that the end products already in solution 

 should pass into the duodenum more rapidly than the albumoses present in 

 the same solution. 



Looking to a decision between these two possibilities, Eeach made experi- 

 ments on surviving stomachs. The animals were killed at the end of the 

 second hour of digestion; the stomach, tied off at both ends and cut out of 

 the body, was maintained for four hours longer in a moist chamber at blood 

 temperature. Since no absorption could take place, this experiment was well 

 calculated to show how far the cleavage of proteid had actually gone. The 

 result was that thirty- two to fifty-six per cent of the total N" in solution (aver- 

 age forty-four per cent) was present in the form of albumoses, and fifty-six 

 per cent in the form of peptones and end products, the latter alone containing 

 some thirty-two per cent of the total nitrogen. It appears therefore that the 

 reason for the ninety per cent and more of albumose nitrogen found in the 

 intravital digestion is not that the enzyme action stops at the albumose stage, 

 but that absorption going on at the same time removes the simpler products 

 very rapidly. 



Partly because of its hydrochloric acid, and partly quite independently 

 thereof (London), the gastric juice plays no small role as an antiseptic. This 

 property of the gastric juice is by no means sufficient to destroy all the Bac- 

 teria which find their way into the stomach ; for very many are found through- 

 out the alimentary canal, and in certain species of animals they play a very 

 important part of which more under the discussion of intestinal digestion. 



Since the food always remains for a tolerably long time in the stomach, 

 this organ most of all must suffer the harmful effects of an ill-adapted diet. 

 We speak also of a digestible or indigestible article of food according as it is 

 digested with greater or less ease in the stomach. It would be very impor- 

 tant, therefore, if general rules could be established as to what is digestible 

 and what is not. Unfortunately, however, this can be done only to a very 

 limited extent, for the stomach is very capricious, and what is well suited to 

 one stomach is unsuited for another. 



