66 PHYSIOLOGY FOR DENTAL STUDENTS. 



which the pepsin itself also dependent, as we have seen, on a 

 preliminary activation by acid then unfolds its action. As the 

 protein becomes progressively broken down into proteose and 

 peptones, the acid becomes more and more absorbed, so that it is 

 some considerable time after gastric digestion has started before 

 any acid is allowed to exist in the free state. It is only after 

 some of it is free that it can hydrolyse sugars or perform an- 

 other important function, namely, act as an antiseptic. In this 

 regard, however, it must be remembered that it is only towards 

 certain organisms that such antiseptic action is displayed, for 

 there may be bacteria in the gastric contents even in cases of ex- 

 cessive secretion of hydrochloric acid. The undoubted tendency 

 for intestinal putrefaction to increase when there is a deficient 

 secretion of hydrochloric acid is probably dependent more upon 

 the delay in digestion which this occasions, than upon any spe- 

 cific antiseptic power of hydrochloric acid. During the time that 

 elapses before a sufficiency of hydrochloric acid has accumulated 

 to perform this function, bacterial fermentation occurs in the 

 stomach contents. Carbohydrates are broken down by this pro- 

 cess, at first into simple sugars and then into lactic acid, which 

 may come to be present in considerable amount before the fer- 

 mentation process is terminated. For these reasons we find 

 that there is relatively much more lactic acid detectable in the 

 gastric contents removed by the stomach tube at an early stage 

 in gastric digestion than later. 



The so-called acid albumin which results from the action of 

 the acid, becomes attacked by the pepsin, which still further 

 breaks it down into so-called proteose and peptones, which do 

 not coagulate by heat and which become progressively more dif- 

 fusible through animal membranes. Although pepsin is capable 

 of carrying the digestive process far beyond the stage of pep- 

 tones, this does not occur in the comparatively short time (about 

 six hours) during which the food remains in the stomach. Slight 

 as is this action of pepsin in the stomach, it nevertheless appears 

 to be of considerable importance for the subsequent digestion of 

 protein by the other proteolytic ferments, trypsin and erepsin 

 (see p. 75), which operate in the small intestine. Thus, a given 



