374 EXAMPLES OF CHEMICAL CORRELATION 



converted into soaps. The origin of this effect is unknown. The 

 Soaps, like other Calcium Precipitants are strong stimulators of nerve 

 fibers and nerve endings, and the contention of Pawlow, that their 

 action upon pancreatic secretion arises reflexly through stimulation of 

 nerve endings in the intestine, is therefore not unfounded. On the 

 other hand it has been suggested that the soaps formed from fats in the 

 intestine, convert prosecretin into secretin or into some substance of 

 like action, which is carried to the pancreas by the blood-stream. 

 Other substances causing an especially abundant flow of pancreatic 

 juice are Chloral Hydrate and Ethyl Alcohol. 



The chemical coordination of the processes of digestion does not 

 end, however, with the coordination of the secretory activities of 

 the digestive glands. If care be taken to excise the pancreas without 

 allowing the tissues to come into contact with the mucous membranes 

 of the intestine, or if the secretin is collected by means of a cannula 

 placed in the duct, so that it is obtained before it touches the intestinal 

 surface, it is found that the fluid is devoid of proteolytic activity. 

 Yet the moment after it arrives within the intestine a very intense 

 proteolytic activity is developed. The reason for this is that Trypsin 

 is not present within the tissues or secretions of the pancreas as such, 

 but in the form of a proteolytically inactive precursor which is desig- 

 nated Trypsinogen. The conversion of trypsinogen into trypsin will 

 not occur spontaneously, under aseptic conditions, even after a period 

 of weeks or months. If, however, the fluid is momentarily acidified 

 and then neutralized, the conversion of trypsinogen into trypsin is 

 found to have been completed within the brief period of exposure to 

 the action of hydrogen ions. A more prolonged exposure results in 

 partial or complete destruction of the trypsin, and since the rate of 

 secondary destruction of the enzyme is proportional to the dissociation 

 or " strength' ' of the free acid, it is safer to employ, for the conversion 

 of the trypsinogen, a weakly dissociated acid, such as Salicylic Acid, 

 which furnishes a sufficiency of hydrogen ions to activate the trypsino- 

 gen but decomposes the active trypsin relatively slowly. 



In actual digestion the activation of the trypsinogen may be brought 

 about in part, it is true, by the admixture of the pancreatic juice with 

 the acid chyme, for the contents of the duodenum are acid to Litmus, 

 although alkaline to Methyl Orange, throughout the greater part of 

 its length. But that another chemical mechanism exists in the intes- 

 tine which is capable of bringing about very rapid and complete activa- 

 tion of trypsinogen is shown by the fact that when the pancreatic 

 secretion is poured into the empty intestine, the trypsinogen which it 

 contains is found to have been activated within a very brief period 

 after its arrival within the intestine; in fact mere contact with the 

 surface of the intestinal mucosa for a few moments suffices to bring 

 about a considerable degree of activation, and under such circumstances, 

 of course, the reaction of the fluid remains consistently alkaline. 



This activation is brought about by a substance which is contained 



