Till BIOCHEMICAL PRO< 185 



occlusion of the arteries, the acid may penetrate the • and ca 



digestion of the stomach walls. Hyperacidity may <»n this account 

 become dangerous, as it lowers the resistance of the cell. 



Tin digestiiH action of hydrochloric acid is closely linked with thai 

 pepsin, with which it will, therefore, be considered. 



The Action of Pepsin 



It is commonlj believed thai before it- tion pepsin twists in the 



cells of the gastric glands as zymogen granules. The chief evidei 

 this belief appears to be thai after considerable activity the amounl 

 zymogen granules in the gland cells is found to be decidedly dimin- 

 ished. By such an hypothesis it is easy to explain certain interesting 

 results concerning the effed of weak alkali on the activities of extri 



of the tin us membrane of the stomach. When the mucous membrane 



stracted with weak acids, the extract is very acti olytically. 



[f this so-called pepsin solution be made faintly alkali) n only 



neutralized, and again made acid, it will be found to have lost much, 

 if not all, of its activity. On the other hand, an aqueous extract ma; 

 rendered slightly alkaline for a short time and still display its digestive 

 activity on subsequent acidification. The extract made with water is 

 therefore much more resistanl toward alkali than that made with weak 

 acid, and the difference is explained on the supposition that the wal 

 extract contains pepsinogen, whereas the acid extract contains pepsin. 



It is believed that there are several varieties of pepsin, because the 

 optimum concentration of acid in which pepsin derived from the stomachs 



of different animals acts is not always the same. Pepsin of tin' d< 

 example, acts besl in a hydrogen-ion concentration corresponding to 

 that .if a 0.05 \. hydrochloric acid solution, whereas thai of the human 

 stomach works besl at a concentration of 0.03 N D nt pepsin 



solutions also show a difference with regard I optimum temp 



ture at which the/ act, and with regard to the nature of tl tein 



which they most readily attack. Thus, the pepsin of a calf's sti.n. 

 digests casein very rapidly, hut coagulated e'_"_ r white only slowly, 

 ereas the pepsin of the pig's stomach acts on both these p 



ahoiit the same pate. 



It is well known that the activity of pepsin can p ly in the 



i i ce of acids, hut this action of acids docs not appear to dep< 

 the hydrogen-ion concentration alo qual quantil the 



same pepsin are mixed with quantities of different acids so that the 

 hydrogen-ion concentration of the mixtures is uniform, it is found that 

 digestion proceeds mosl rapidly with hydrochloric acid and leasl rapidly 

 with sulphuric acid. Th( SO 'ems. the unfavorable 



