DIGESTION 155 



secretion is abolished, but the local vaso-motor mechanism is unimpaired, 

 for stimulation of the nerve, as in the previous instance, gives rise to a dilata- 

 tion of the vessels and an increased blood-supply. There is thus abundant 

 proof that the chorda tympani contains two sets of fibers one regulating 

 the blood-supply to the gland, the other stimulating the secretor cells. 



The Glosso-pharyngeal Nerve. The trunk of this nerve also contains 

 efferent autonomic fibers, secretor and vaso-dilatator, which have their 

 origin in the salivary nucleus and the vaso-dilatator nucleus respectively. 

 From their origin they pass outward in the trunk of the glosso-pharyngeal. 

 After a short course they leave this nerve and enter the tympanic cavity 

 as a distinct nerve when it is known as the nerve of Jacobson, and finally 

 arborises around the cells of the otic ganglion. From the otic ganglion 

 post-ganglionic fibers arise which enter the auriculo-temporal branch of 

 the fifth nerve and by this route reach the cells of the parotid gland and 

 the blood-vessels by which it is surrounded. 



The influence of the efferent fibers in the trunk of the glosso-pharyngeal 

 on the parotid gland is similar to the influence of the chorda tympani on the 

 submaxillary gland ; for if the glosso-pharyngeal nerve or its post-ganglionic 

 continuations in the auriculo-temporal nerve be stimulated in any part of its 

 course with induced electric currents there follows a dilatation of the blood- 

 vessels and an abundant discharge of a thin saliva rich in water and salts 

 but poor in the amount of organic matter. Division of the glosso-pharyngeal 

 nerve, extirpation of the otic ganglion or division of the auriculo-temporal 

 nerve is followed by a loss of reflex secretion. Stimulation of the branch 

 connecting the glosso-pharyngeal with the otic ganglion (Jacobson's nerve) 

 gives rise to the secretion as shown by Heidenhain. Division of the nerve 

 is also followed by a loss of reflex secretion. 



The Sympathetic Nerves. The efferent nerve-fibers that conduct nerve 

 impulses to the cells of the salivary glands and to the blood-vessels 

 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 con- 

 nected through the intermediation of fine terminal branches. From 

 this ganglion non-medullated nerve-fibers sympathetic nerves proper 

 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, sublingual, or 

 parotid glands. If the sympathetic nerve in the neck, especially in the dog, 

 be divided and the peripheral end stimulated with induced electric currents, 

 there is at once a contraction of the smaller blood-vessels of the submaxillary 

 and sublingual glands 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 stimulated. 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 sympathetic 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 secretor cells, for sub- 

 sequent stimulation of the auriculo-temporal nerve not only causes an 



