DIGESTION AND ABSORPTION IN THE STOMACH. 777 



tion given above, the several stages in peptic digestion are repre- 

 sented as following in sequence. It should be stated, however, 

 that many authors consider that even in the beginning of the 

 digestion the protein molecule may be split into several complexes, 

 and that some of the end-products may be formed very early in 

 the action. The end-result of the action of the pepsin in the 

 stomach is the conversion of more or less of the protein of the 

 food into the simpler and more soluble peptones and proteoses. 

 The action of the enzyme is preparatory to the more complete 

 hydrolysis that takes place in the intestine under the influence of 

 the trypsin and erepsin, for, as we shall see, the protein of the food 

 is not absorbed into the blood as peptones, but suffers first a further 

 hydrolysis to amino-acids and peptids. While the pepsin is, there- 

 fore, a relatively weak proteolytic enzyme, it plays an important 

 role in initiating the splitting up of the protein molecule, and its 

 value in this respect is increased by the fact that it is adapted to 

 act upon proteins of all kinds and bring them to a stage suitable for 

 the more complete action of the proteolytic enzymes of the intes- 

 tinal secretion. 



In judging the digestive action of any given specimen of natural 

 or artificial gastric juice it is customary to measure the rapidity 

 with which an insoluble protein is converted into a soluble form. 

 The method most commonly employed is that devised in Pawlow's 

 laboratory by Mett. The Mett test is made by sucking white of egg 

 into a thin-walled glass tube having an internal diameter of 1 to 2 

 mms. The egg-albumin is coagulated in the tube by immersing it for 

 five minutes in water at 95° C. After some time the tube is cut into 

 lengths of 10 to 15 mms. and these are used to test the digestive action 

 or amount of pepsin. One or more of the tubes are placed in the 

 solution to be measured and kept for ten hours at bod}^ temperature. 

 The digestive power is measured in terms of the length in millimeters 

 of the column of egg-albumin that is dissolved. The relative amounts 

 of pepsin in solutions compared in tliis way are determined by the 

 law of Schiitz, according to wliich the digestive power is proportional 

 to the square root of the amount of pepsin. If in two specimens of 

 gastric juice the number of millimeters of egg albumin digested 

 was in one case two and in the other three, the pepsin in the two 

 solutions would be as the squares of the numbers, as 4 to 9. 



The Rennin Enzyme (Rennet, Chymosin). — The property 

 possessed by the mucous membrane of the calf's stomach of curdling 

 milk has been known from remote times, and has been utilized in the 

 manufacture of cheese and curds. This action takes place with 

 remarkable rapidity under favorable conditions, a large mass of milk 

 setting to a firm coagulum within a very l)rief time. It has been 

 shown that this effect is due to an enzyme— rennin or rennet. The 

 rennin, like the pepsin, is supposed to be formed in the chief cells of 



