130 THE DRil'XTIVK I-LI'IDS. 



ogen only is present are incapable of digesting albumins. In such 

 cases, as I have just said, hydrochloric acid is absent. If then 

 the solution is acidified to the extent of from 0.1 to 0.3 pel- 

 cent., and the dissolution of a flake of boiled beef-fibrin now occurs, 

 the presence of the zymogcn may be inferred. 



Quantitative Estimation of Pepsinogen. The determination of the 

 absolute quantity of pepsinogen in the gastric juice, as that of pep- 

 sin, is not possible. Relative values, however, mnv be obtained by 

 the following method, as suggested by Boas : To this end, specimens 

 of the gastric juice are variously diluted with distilled water in the 

 proportion of 1 : 5, 1 : 10, 1 : 20, etc. A known quantity of coagu- 

 lated egg-albumin or serum-albumin is then added to each tube, 

 as also 1 or 2 drops of a 0.3 per cent, solution of hydrochloric acid, 

 for every 10 c.c. The tubes are kept at a temperature of about 

 40 C., when the degree of dilution is noted at which the albumin is 

 still dissolved. The greater the degree of dilution at which this 

 occurs, of course the greater is the amount of pepsinogen that is, 

 of pepsin present. 



Should it be desired to exclude definitely the presence of pepsin 

 and pepsinogen in the stomach, 200 c.c. of a decinormal solution of 

 hydrochloric acid are introduced into the organ through a tube, and 

 the remaining liquid removed after one-half hour. If this fluid 

 then contains no pepsin, the absence of the zymogen may also be 

 inferred. 



Chymosin. Chymosin, or rennin, like pepsin, is secreted by the 

 central cells of the gastric glands in the form of a pro-enzyme, which, 

 like the pepsinogen, is then transformed into the corresponding fer- 

 ment by the hydrochloric acid of the gastric juice. It is to be 

 noted, however, that calcium chloride or any other soluble calcium 

 salt is likewise capable of bringing about this result. The specific 

 action of chymosin is exerted upon milk or lime-containing solutions 

 of casein, which are coagulated in neutral and even feebly alkaline 

 solutions. Unlike pepsin, chymosin is not a proteolytic ferment, 

 and its action ceases with the formation of paracasein. It is there- 

 fore surprising to note that chymosin is found not only in the 

 stomachs of mammals, but also in other vertebrate animals, and 

 even in certain plants, where casei'n as a food-stuff certainly does not 

 enter into consideration. Our knowledge of ferments in general, how- 

 ever, is as yet very defective, and, as a matter of fact, we are acquainted 

 only with the more manifest reactions of these bodies, while it is 

 quite possible that they possess other important properties of which 

 we are now in ignorance. It is conceivable, moreover, that differ- 

 ent varieties of chymosin exist, which, as a class, are all capable 

 of coagulating casein, but which differ from each other in other 

 respects and serve other purposes. 



While chymosin is also active in feebly acid solution, it is gradu- 

 ally destroyed at a temperature of from 37 to 40 C. when exposed 

 to the action of gastric juice containing 0.3 per cent, of hydrochloric 



