CHEMICAL CORRELATION OF PROCESSES OF DIGESTION 375 



in the secretions of the intestinal glands comprising tlje so-called Succus 

 Entericus. The activating constituent is designated Enterokinase, 

 and because of the fact that it is destroyed or inactivated by heat- 

 ing, and is furthermore active in very small quantities, it has been 

 generally assumed to be an enzyme, and in fact Pawlow has termed it a 

 "ferment of ferments." Nevertheless the proof that enterokinase is 

 an enzyme is very imperfect. Many substances are modified by heat 

 which are not enzymes, of course, and the small amount of the material 

 required to activate a large volume of pancreatic juice may merely be 

 expressive of the minute quantity of trypsin which is actually present 

 in the secretion of the pancreas. We have no method of quantitatively 

 estimating trypsinogen and enterokinase except in terms of each other 

 and we have no data which could enable us to arrive at an estimate of 

 the actual weight of trypsinogen which is activated by a given weight 

 of enterokinase. More conclusive evidence of the enzymatic character 

 of enterokinase would be afforded if we were to find that a limited 

 quantity of succ is e itericus will activate very large quantities of 

 pancreatic juice provided, only, that sufficient lapse of time be allowed 

 for the completion of the process. But from the results of Hamburger, 

 Hekma and others, it appears that the contrary is actually the case, 

 and that there is a quantitative relationship between the amount of 

 succus entericus which is added to pancreatic juice and the amount 

 of trypsin which is produced. 



We have stated that the pancreatic juice, as produced by the secre- 

 tory cells of the pancreas, is proteolytically inactive. While this is 

 generally the case, it is*not necessarily or invariably so. The juice 

 obtained by the action of Secretin is, it is true, invariably inactive, but 

 juice obtained by stimulation of the secretomotor fibers in the vagus 

 usually contains active trypsin, and juice containing preactivated 

 trypsin may also be obtained after the administration of certain food- 

 stuffs, particularly diets containing a high proportion of meat. The 

 seat and mechanism of this activation is unknown. 



In general, however, it is evident that the proteolytic powers of 

 pancreatic juice must be much enhanced by admixture with. succus 

 entericus, in part through the activation of trypsinogen by entero- 

 kinase and in part owing to the fact that succus entericus contains 

 Erepsin, an enzyme capable of splitting peptones or casein, but not 

 other proteins, to amino-acids. The digestion of protein by mixed 

 proteolytic enzymes is always more rapid and complete than when a 

 single enzyme is present, because different enzymes attack different 

 linkages preferentially so that in the presence of two or more enzymes 

 a larger number of amino-acid linkages are rendered susceptible to rapid 

 disruption. This being the case it is a fact of interest and importance 

 that pancreatic juice itself, according to Pawlow, stimulates, by its 

 presence, the secretion of succus entericus. At all events during gastric 

 digestion the secretion of fluid from the glands of the intestine is very 

 small, but after passage of the chyme into the intestine and the coinci- 



