I;L> INTERNAL SECRETION 



enzymes and proteins but poor in alkalies. The chemical 

 secretion, on the contrary, is thin and watery, contains little 

 enzyme or protein, and js rich in alkali. 



Gley has recently given the accompanying classification of 

 substances which excite the flow of pancreatic juice (p. 63). 



Gley points out that the part played by the acid of the gastric 

 juice as an excitant of the flow of pancreatic juice is altogether 

 special, since it acts at the same time through the chemical 

 mechanism in liberating secretin, and by means of a nervous 

 mechanism, that is to say, by reflex excitation of the secretory 

 nerves to the pancreas. 



V. Fiirth and Schwarz believe that secretin is not a 

 definite, single substance, but a mixture of several gland- 

 stimulating substances, of which choline can be recognized 

 as one. 



With regard to the mechanism of the secretion of the intes- 

 tinal juice, nothing definite is yet known. We know that the 

 juice when it is formed is essential for the activation of the 

 pancreatic juice by means of the enterokinase. The tryp- 

 sinogen is only converted into the proteolytic ferment trypsin 

 after the action of the enterokinase. According to Pavlov, the 

 secretion of the succus entericus depends upon two factors : 

 (1) The mechanical distension of the alimentary canal; (2) 

 the presence of the pancreatic juice. Bayliss and Starling 

 consider it probable that the secretion of succus entericus is 

 called forth by the chemical action of the pancreatic juice upon 

 the glands in the intestinal wall. Delezenne and Frouin 

 report that the intravenous injection of secretin provokes an 

 immediate and abundant secretion of succus entericus. 



It has been suggested that the increase in red and white cells 

 in the blood after a meal is due to the stimulation of the bone- 

 marrow by secretin. 



According to Lombroso the prime factor in the secretion of 

 the intestinal juice is the action of chemical substances which 

 are produced during normal digestion, and act on the nerve 

 endings of the mucous membrane of the intestine. 



It has been suggested that secretin may be useful as a drug 

 with the object of increasing the pancreatic flow. But it must 

 be noted that it is absent from some commercial preparations 

 supposed to contain it, and even if it is present it would be 

 I'-troyed quickly by the gastric juice and the trypsin. It 



