DIGESTION AND ABSORPTION IN THE STOMACH. 715 



heat nor precipitated when its solutions are completely saturated 

 with ammonium sulphate. According to the schema and descrip- 

 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 in the very 

 beginning of the action. All that we can state very positively 

 is that the protein molecules undergo a series of hydrolytic cleav- 

 ages, the end-result of which is that in place of the originally very 

 large molecule with a weight of 5000 to 7000 there is obtained a 

 number of much smaller and much more soluble molecules w T hose 

 molecular weights are perhaps only 250 to 400 or less. 



It was formerly believed that pepsin was not able to split the complex 

 protein molecule into compounds of a simpler structure than the peptone. 

 But a number of recent authors have stated that if time enough is given 

 the breaking up of the protein molecule may be as complete as after the action 

 of trypsin, or after hydrolysis by acids (see Proteins in appendix). That 

 is, along with the peptone or in place of it are found certain simpler bodies 

 which no longer give the biuret reaction, but are precipitable by phospho- 

 tungstic acid and for which Hofmeister proposes the general name of pep- 

 toids. They would correspond, also, apparently, to the group of compounds 

 designated by Fischer as peptids or polypeptids. In addition, many of the 

 amino-acids and nitrogenous bases which constitute the final end-products 

 of the breaking up of the protein molecule may be found.* 



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 body 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 this way are determined by the 

 law of Schiitz, according to which 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 digestive powers of 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 



* See Hofmeister, " Ergebnisse der Physiologic," vol. i, part i, 796, 1902. 



