THE GASTRIC JUICE. 137 



through a specific activity on the part of the cells, from food- 

 material which is supplied by the lymph. 



A solution of the pro-enzymes of the gastric mucosa that has 

 been freed from albumins does not give the common reactions of 

 the true albumins. From such solutions the pro-enzymes are not 

 precipitated by dialysis, but it is interesting to note that on long- 

 continued dialysis they are rendered inactive ; they are then appar- 

 ently destroyed. To a slight extent they will pass through 

 Chamberland filters, as well as those of Kitasato ; the propepsin 

 passes through somewhat more readily than the prochymosin. 



Of interest also is the tendency of the proferments to adhere to 

 solid substances, and it has been shown that they possess selective 

 properties in this respect, which are not the same in both always. 

 Lycopodium, for example, will carry down the pepsinogen, but 

 not the chymosinogen. Charcoal, powdered marble, and calcium 

 sulphate will carry down both. 



Whether or not the transformation of the proenzymes into the 

 corresponding ferments occurs in the bodies of the cells has not been 

 definitely decided. It appears, however, that in the majority of 

 animals which have been examined in this direction the glands 

 secrete only the proenzymes, and that these are then rendered 

 physiologically active by the hydrochloric acid of the gastric juice. 

 A solution of propepsin, which may be obtained by macerating in 

 glycerin the mucous membrane of a fasting animal, is thus in itself 

 inert, but is rendered active at once when hydrochloric acid is added 

 to the extent of from 0.1 to 0.2 per cent. It is indeed supposed 

 that pepsin, which in itself is inactive like its zymogen, combines 

 with hydrochloric acid, which alone is similarly inert, as regards its 

 digestive ability, to form a compound acid, the so-called pepsin- 

 hydrochloric acid. On coming in contact with albuminous mate- 

 rial this is supposedly decomposed, with the formation of nascent 

 hydrochloric acid, which then acts as the active digestive principle, 

 while the liberated pepsin combines with a new portion of hydro- 

 chloric acid, and thus serves as an acid-carrier. On this question, 

 however, a uniformity of opinion does not exist ; still, the hypoth- 

 esis is an attractive one, and has a good deal in its favor. If we 

 thus regard the action of a ferment as essentially influencing the 

 rapidity of reaction, the action of the weak hydrochloric acid of 

 the gastric juice could be compared to the effect of stronger solu- 

 tions upon albumins under the application of heat. 



Pepsin. Pure pepsin occurs in the form of minute globules, which 

 resemble the globulites of egg-albumin, but are somewhat smaller. 

 Their diameter does not exceed 15-20 //. They are not doubly 

 refracting. The substance is white when perfectly pure and is 

 not hygroscopic. It is soluble in water, dilute acids, and glycerin. 

 From its aqueous solutions it can be precipitated by half-saturation 

 with ammonium sulphate, and it is also thrown down on dialysis. 



When acidified with hydrochloric acid to the extent of from 0.1 



