102 LANGLEY'S RESEARCHES ON PEPSINOGEN. [BOOK n. 



schiff'spro- Schiff observed that when a stomach was treated 

 pepsin. -with acidulated water, the digestive power of the fluid 



increased for some weeks. This he considered to be due to the 

 presence of ' propepsin,' which was only slowly converted into pepsin. 

 Apparently however pepsinogen is converted into pepsin with great 

 rapidity by even very dilute hydrochloric acid. 



Langiey'sex- Although Ebstein and Griitzner had brought for- 

 periments es- ward evidence which rendered the existence of pepsino- 

 tabiishing the g en mos ^ probable, the most conclusive proof of its 

 rea ^y has been adduced by Langley. This observer 

 shewed that pepsin and its precursor pepsinogen be- 

 have very differently when digested at 40 with solution of sodium 

 carbonate, containing from 0*5 to TO per cent, of Na 2 C0 3 , the former 

 body being very readily destroyed by it, the latter comparatively 

 slowly ; the action of the alkaline salt causing first, however, the 

 appearance by degrees of pepsin. When an active hydrochloric 

 acid extract of the mucous membrane of the stomach is neutralised 

 and digested with the above solution and afterwards re-acidified, it 

 is found to have lost its proteolytic power. On the other hand, when 

 a watery extract of the mucous membrane is digested for an equal 

 time with solution of Na 2 C0 3 of the same strength, on subsequently 

 acidifying it is found to possess proteolytic powers 1 . 



Pepsinogen is, according to Langley, soluble in water, and so is 

 soluble in glycerin, unless this be anhydrous; it is, however, more 

 soluble in salt solution. 



From his researches Langley concludes, " That the gastric glands 

 contain no ferment during life, but much zymogen or substance 

 capable of giving rise to ferment." 



" That by far the greater part of the zymogen can be seen in the 

 chief (central) cells in the form of granules." 



" That during digestion, the granules are usually used up in such 

 a manner as to give rise to an outer non-granular and an inner 

 granular zone in the chief cells." 



Further re- Continuing his researches in conjunction with 



searches of Edkins 2 , Langley has been able to confirm his original 

 Langley in as- conclusions and to add considerably to our knowledge 

 f the relations of pepsinogen and pepsin and the 

 circumstances under which the latter is produced from 

 the former. The following were their chief results : 



Pepsin is very rapidly destroyed by alkalies and by alkaline salts. 

 The principal conditions which influence the rate of destruction of 

 pepsin by sodium carbonate are, the strength of the solution of the 



1 J. N. Langley, 'On the Histology of the Mammalian Gastric Glands, and the 

 relation of Pepsin to the Granules of the chief Cells.' Journal of Physiology, Vol. in. 

 p. 269. 



2 J. N. Langley and J. S. Edkins, 'Pepsinogen and Pepsin.' Journal of Physio- 

 logy, Vol. vn. p. 371. 



