DIGESTION AND ABSORPTION IN THE STOMACH. 779" 



more easily digested under the conditions that exist in the body 

 after it has been brought into a solid form, or, perhaps, the coagu- 

 lation of the casein ensures that it will be retained in the stomach 

 and be submitted to gastric digestion, instead of being ejected 

 promptly into the duodenum, as happens with liquid material. 

 The action of rennin goes no further than the curdling; the diges- 

 tion of the curd is carried on by the pepsin, and later, in the intes- 

 tines, by the trypsin, as in the case of other proteins.* 



Rennin is found elsewhere than in the gastric mucosa. It has been 

 described in the pancreatic juice, in the testis, and in many other organs 

 as well as in the tissues of many plants. In fact, wherever proteolytic enzymes 

 are found there also some evidence of a curdling action on milk may be ob- 

 tained. For this reason some observers f have taken the view that the milk 

 coagulation is not due to a specific ferment, but is an action of the pepsin itself. 

 That is, the proteolytic enzyme is capable of causing the change from casein 

 to paracasein as well as the hydrolysis of the protein. This view is opposed to 

 the prevalent opinion regarding the specificity of enzyme actions, and is con- 

 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 



* For references to very abundant literature, consult Oppenheimer, hoc. cil. 

 t See Pawlow and Parastschuk, "Zeitschrift f. physiol. Chemie," 42, 415, 

 1904; Burge, "American Journal of Physiology," 29, 330, 1912. 



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



