CHAPTER VI. 

 SECRETION DIGESTION ABSORPTION. 



I. SECRETION OF SALIVA. 



Mechanism of Secretion. Demonstration. Secretion may 

 be divided into two stages the productive stage, during which the 

 secretory products are being formed in the gland cells, and the 

 eliminative stage, during which the products already formed pass 

 out of the cells and through the gland ducts to the surface where the 

 secretion performs its particular function. 



The elimination of the secretion may be brought about either 

 by a nervous stimulus of the gland cells or a chemical stimulus, or 

 both. The mechanism of the elimination of the salivary secretions 

 furnishes an excellent example of the influence of nervous im- 

 pulses. This is not of so much importance in itself, as it is in serv- 

 ing as a type of the nervous mechanism of secretions in general. 



Of the salivary glands, the one which has been chiefly studied 

 and used to demonstrate this mechanism is the submaxillary 

 gland. 



Place a dog under ether and tie to the dog-board. Clip the hair 

 from the jaws and neck and shave the skin. Make an incision 

 through the skin of the lower jaw, along its inner border, beginning 

 just in front of the insertion of the anterior belly of the digastric 

 muscle and extending backward through the platysma muscle to 

 the transverse process of the first cervical vertebra. 



Expose the jugular vein and its, branches, including those which 

 drain the submaxillary gland. Tie all venous branches which pass 

 below and in front of the gland, excepting those which come from 

 the gland itself. The veins should be tied between two ligatures, 



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