ii EXTERNAL DIGESTIVE SECRETIONS 121 



was extracted with the pepsin, and yielded a further quantity of 

 pepsin when hydrochloric acid or even sodium chloride were added. 

 Langley afterwards found that on extracting the gastric mucous 

 membrane with a 1 per cent solution of sodium carbonate, and acid- 

 ulating with hydrochloric acid, the extract contained pepsin, as 

 shown by its digestion of proteins. As sodium carbonate abolishes 

 the activity of pepsin, the gastric glands must contain a substance 

 other than pepsin, which is not destroyed by the soda solution, 

 and is readily transformed by acids into pepsin. This substance 

 is pepsinogen. 



Griitzner performed a series of experiments to determine the 

 maximal quantity of pepsin which can be extracted by excess of 

 acid, with long digestion at 40 C., from the fundus and pyloric 

 mucous membrane of dogs killed at various hours after a meal. 

 He found that the pepsin is maximal in the fundus glands during 

 hunger, and minimal nine hours after a meal : in the pylorus glands 

 it increases in the first hours after a meal, reaches its maximum 

 at the ninth hour, and then decreases slowly. This fact agrees well 

 with the modifications observed in the cells of the pyloric glands, 

 which (unlike the changes in the fundus) increase in the first 

 hours after a meal, and then decrease slowly, signifying that 

 in the first hours after a meal more pepsinogen is formed than 

 is simultaneously excreted as pepsin. 



The process by which pepsinogen is normally transformed 

 into pepsin during the digestive period is still imperfectly known. 

 It was suspected, on the analogy of the transformation by the 

 pancreas of trypsinogen into trypsin, that the formation of 

 pepsin from pepsinogen might also be due to the action of an 

 internal secretion of the spleen, which becomes actively turgid 

 during digestion. This hypothesis, which Baccelli advanced in 

 1868, has not been fully worked out, possibly because excessive 

 value has been put upon the fact that animals deprived of their 

 spleen are able to live and digest perfectly. This objection might 

 be met by the further and well-established fact that it is also 

 possible to live without a stomach. At all events the assumption 

 that the spleen takes part in the formation of pepsin does not 

 exclude the possibility of the formation and secretion of pepsin 

 without a spleen. 



The congested spleen of a dog in full digestion is excised, and 

 divided into small fragments, which are rubbed up in a mortar 

 with powdered glass. This paste is placed in a retort, with five 

 times its volume of 4 per cent boracic acid. This is digested in 

 a stove at 37 C. for six hours, and on filtering a transparent dark- 

 red fluid is obtained. 



Two equal parts of this extract, 15 c.c. each, are poured into 

 two small flasks, with 15 c.c. solution of 04 per cent hydrochloric 

 acid, and | gramme of raw fibrin, ready swollen by the action of 



