790 PHYSIOLOGY OF DIGESTION AND SECRETION. 



tradicted by a number of observers. Burge, for example, reports that if a 

 solution showing both peptic and rennetic action is submitted to the action of 

 an electric current the peptic power is destroyed completely in a certain time, 

 while the rennetic action remains in full force. 



Another interesting fact concerning rennin is that when injected into an 

 animal it causes the formation of a specific antibody known as antirennin, 

 which may be detected in the blood. This antirennin added to milk prevents 

 its curdling by rennin, giving a result, therefore, similar to the reaction between 

 toxins and antitoxins. 



The Digestive Changes Undergone by the Food in the 

 Stomach. In addition to the pepsin and rennin various observers 

 have described other enzymes in the gastric juice or gastric mem- 

 brane, but the evidence at hand is uncertain regarding these 

 latter. As was said above, it is probable that the ptyalin 

 swallowed with the food continues to exert its action upon the 

 starchy material in the fundus for a long time, so that in this way 

 the starch digestion in the stomach may be important. Regarding 

 the fats, it is usually believed that they undergo no truly digestive 

 change in the stomach. They are set free from their intimate 

 mixture with other food stuffs by the dissolving action of the gas- 

 tric juice upon proteins, they are liquefied by the heat of the body, 

 and they are disseminated through the chyme in a coarse emulsion 

 by the movements of the stomach. In this way they are mechan- 

 ically prepared so that the subsequent action of the pancreatic 

 juice is much favored. Some observers* state that the gastric 

 juice does normally contain a lipase capable of causing hydrolytic 

 cleavage of the neutral fat into fatty acid and glycerin. It would 

 appear, however, that this lipase is readily destroyed by an acidity 

 of 0.2 per cent. HC1, so that if it is of functional importance in 

 gastric digestion its action, like that of the ptyalin, must be con- 

 fined to the early period of digestion before the contents of the. 

 stomach have reached their normal acidity. Regarding the proteins, 

 the practical point of interest is as to how far they are digested dur- 

 ing their stay in the stomach. It seems probable that this question 

 does not admit of a categorical answer that is, the extent of the 

 digestion varies under different circumstances; with the consist- 

 ency of the food, the duration of its stay in the stomach, etc. In 

 some experiments reported by Tobler it is stated that 48 per cent, 

 of a given amount of protein passed through the pylorus as pep- 

 tones or proteoses, about 20 per cent, entered the intestine un- 

 digested, and 20 to 30 per cent, was absorbed from the stomach. 

 In the liquid material (chyme) forced through the pylorus into 

 the duodenum one may find unchanged proteins, primary or 

 secondary proteoses, peptones, or, possibly, cleavage products be- 

 yond this stage. It is stated, however, that most of the material 

 is in the form of proteoses (London). The true value of peptic 

 digestion is not so much in its own action as in its combined action 

 * Hall and Keeton, "Journal of Biological Chemistry," 1917, 32, 127. 



