CHAPTER L 



PHYSIOLOGY OF THE DIGESTIVE GLANDS (Cont'd) 



Up to the present we have been concerned with the physiological activi- 

 ties of digestive glands in general, but now we must study each of them 

 separately in order to find out the conditions under which they become 

 stimulated to activity in the normal process of digestion. The secretion 

 of each gland has a definite role assigned to it in the complex and lengthy 

 process of digestion. It takes up its work where the preceding secre- 

 tion left off; e.g., the pepsin of gastric juice digests protein so far as 

 proteoses and peptone ; the trypsin of pancreatic juice then attacks the 

 proteoses and peptone, and the resulting loAver degradation products 

 are finally attacked by the erepsin of the intestinal juice. The secre- 

 tions of the various glands are, therefore, required in a certain definite 

 order — they are correlated; and we must now give some attention to the 

 precise conditions upon which the activity and correlation depend. 



THE NORMAL CONDITIONS UNDER WHICH THE GLANDS 

 BECOME STIMULATED TO INCREASED ACTIVITY 



To make possible such observations on the normal activities of the 

 glands, a preliminary operation has to be performed so as to bring the 

 duct of the gland to the surface of the body and permit of the observa- 

 tion of its secretory activity after the animal has recovered from the 

 immediate effects of the operation. We owe to Pavlov 1 the surgical 

 technic by which these conditions can be fulfilled. The general principle 

 of the operation, in the case of glands provided with ducts, consists in 

 making a circular cut through the mucous membrane surrounding the 

 opening of the duct and then, after dissecting the duct free, stitching 

 the edges of the cut to the skin wound. Healing then takes place without 

 the formation in the duct of any stricture .due to cicatricial tissue. After 

 the wound has healed, the secretion can readily be collected in a receiver 

 attached over the duct fistula, the animal being in every other way in a 

 perfectly normal condition. In the case of glands not provided with a 

 duct, other methods must be adopted to collect the secretions. These 

 Avill be described elsewhere. 



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