IS 2 PHYSIOLOGICAL CHEMISTRY. 



nin, was pointed out. Whether these bodies are always se- 

 creted simultaneously and in corresponding amounts is not 

 definitely known, but that this is the case is often assumed; 

 it will be recalled that the followers of the Pawlow school 

 consider the enzymes identical, as referred to above. In 

 fact, one of the clinical methods in use for the estimation of 

 " peptic " activity is based on the measurement of the rennet 

 action through milk coagulation. The process seems, how- 

 ever, of doubtful value. In speaking of gastric digestion in 

 adults we are concerned mainly with what takes place through 

 the action of pepsin, which will now be discussed. 



PEPTIC DIGESTION. 



In presence of free acids of the so-called " stronger " type 

 pepsin has the power of effecting remarkable changes in pro- 

 tein substances, which have been the subject of numerous in- 

 vestigations. In the stomach hydrochloric acid only comes 

 into play and it first gradually converts the proteins present 

 into acid-albumins or syntonin bodies. This is the preliminary 

 stage in the digestion of these food substances and must be 

 accomplished before the other steps in the stomach are pos- 

 sible. 



In this reaction the hydrochloric acid enters into a kind of 

 combination with the protein. The product has just been 

 spoken of as acid albumin, but it is evidently through the basic 

 character of the protein complex that the combination can take 

 place. The protein here is in effect a very weak base. The 

 amount of acid which may be so held is considerable, and may 

 in fact amount to 5 per cent or more of the weight of the 

 protein. With certain of the derived protein products the 

 weight of hydrochloric acid combined is even larger, at times 

 as much as 15 per cent of the protein weight being so held. 

 These derived products are hydrolysis products with smaller 

 molecular weight and evidently more available hydroxyl or 

 amino groups to hold the acid. 



It is generally held, as just stated, that this acid fixation is 



