DIGESTION. 169 



be stimulated by the induced electric current, there follows a dilata- 

 tion of the blood-vessels and an abundant discharge of a thin saliva, 

 rich in water and salts, but containing a small amount of organic 

 matter. Division of the nerve, extirpation of the otic ganglion, 

 division of Jacobson's nerve, is followed by a loss of reflex secretion. 

 Stimulation of Jacobson's nerve, as shown by Heidenhain, gives rise 

 to the secretion. 



The sympathetic fibers which influence the salivary secretion 

 emerge from the spinal cord mainly through the second, third, and 

 fourth thoracic nerves. After passing into the sympathetic chain 

 they ascend to the superior cervical ganglion, with the cells of which 

 they become connected through the intermediation of fine terminal 

 branches. From this point non-medullated nerve-fibers follow the 

 branches of the external carotid artery to the different glands. There 

 is no evidence that these fibers have any connection, anatomic or 

 physiologic, with local ganglia at or near the submaxillary or sub- 

 lingual glands. If the sympathetic nerve in the neck, especially in 

 the dog, be divided and the peripheral end stimulated with the in- 

 duced electric current, there is at once a contraction of the smaller 

 blood-vessels of the gland and a diminution of the blood-supply, a 

 result showing the presence of vaso-constrictor fibers. Nevertheless 

 both the submaxillary and sublingual glands pour out a saliva which 

 is different from that poured out when the chorda tympani is stimu- 

 lated. The quantity is less, it is more viscid, richer in organic matter, 

 of a higher specific gravity, and more active in the transformation of 

 starch into sugar. Stimulation of the fibers passing to the parotid 

 gland is followed by contraction of the vessels and an abolition of the 

 secretion; but at the same time there is an increased activity of the 

 secretory cells, for subsequent stimulation of the auriculo- temporal 

 nerve not only causes an increase in the amount of water and in- 

 organic salts, but an increase also in the amount of organic matter 

 far beyond that produced when the auriculo-temporal has alone been 

 stimulated. Histologic examination shows that the small ducts of 

 the gland are filled with thick organic matter after stimulation of 

 the cervical sympathetic. 



DEGLUTITION. 



Deglutition is that part of the digestive process which is concerned 

 in the transference of the food from the mouth through the pharynx 

 and esophagus into the stomach. This is an extremely complex act 

 and involves the action of a large number of structures, all of which 

 are made to act in proper sequence under the coordinating influence 

 of the nervous system. The deglutitory canal consists of the mouth, 

 pharynx, and esophagus, each of which presents certain anatomic 

 features on which its physiologic action depends. 



