THE GASTRIC JUICE. 139 



its weight of fibrin in seven hours. The much more impure 

 commericial forms are, of course, far less active, but many of them 

 possess remarkable digestive power. 



The ability on the part of pepsin to digest albumins is, however, 

 limited ; and with an increase in the amount of digestive products 

 formed, its activity gradually diminishes and finally ceases. This 

 can be obviated in a measure by removing these products as they 

 are formed, and may be artificially accomplished by allowing the 

 digestion to take place in a parchment tube which has been sus- 

 pended in dilute hydrochloric acid. The peptones which are formed 

 then pass from the tube by dialysis, and in this manner digestion 

 can be carried much further than under other conditions. Com- 

 plete digestion, however, may even then not be achieved. 



llegarding the chemical nature of pepsin, our knowledge has 

 been greatly extended through the researches of Pekelharing, and 

 Nencki and Sieber. From the fact that it is possible to prepare 

 pepsin solutions which actively digest albumin, but do not show 

 the common albumin reactions, it has been concluded that pure 

 pepsin is probably not an albumin. The researches of the investi- 

 gators just mentioned, however, seem to show conclusively that it 

 is an albumin nevertheless, although it cannot be classed with any 

 of the known forms. It contains no phosphorus, but nevertheless 

 yields xanthin-bases on hydrolysis with alkalies. Both Friedenthal 

 and Pekelharing have shown that a pentose can be obtained from 

 it, and quite recently the latter has isolated a peculiar acid on 

 hydrolysis with alkali which gives the biuret and xanthoproteic 

 reaction, as also that of Adamkiewicz and Millon. This acid is 

 termed pepsinie acid, and is derived from a coagulation-product of 

 pepsin, which in turn is formed when acid solutions of the pepsin 

 are rapidly heated over the free flame. Both the coagulation- 

 product as also the pepsinie acid, like all albumins, are laevorotatory. 

 Elementary analysis of the pure pepsin, obtained from dogs that 

 had been operated on by Pawlow's method (oasophageal and gastric 

 fistulas), as also of the coagulation-product and the acid, gave the 

 following average results : 



C H N S Cl 



Pepsin 51.99 7.07 1444 1.63 0.49 



Coagulation-product. . . . 50.35 6.98 14.90 1.64 



Pepsinie acid 50.79 7.02 14.44 1.08 



From the mode of origin of pepsinie acid it is, of course, clear 

 that the substance can contain no loosely combined sulphur. Note- 

 worthy is the fact that the pepsin contains chlorine, and the evi- 

 dence appears to be conclusive that the chlorine is an actual con- 

 stituent of the pepsin molecule. 



Formalin when added to a solution of pure pepsin to the extent 

 of 2 to 3 per cent, produces no appreciable effect upon the digestive 

 power even after days. 



While pepsin is probably constantly found in the- gastric juice of 



