DIGESTION. 239 



time, although the blood-supply is necessarily absent. These experi- 

 ments serve to prove that the chorda contains two sets of nerve-fibres, 

 one set (vaso-dilator) which, when stimulated, act upon a local vaso- 

 motor centre for regulating the blood-supply, inhibiting its action, and 

 causing the vessels to dilate, and so producing an increased supply of 

 blood to the gland; while another set, which are paralyzed by injection 

 of atropin, directly stimulate the cells themselves to activity, whereby 

 they secrete and discharge the constituents of the saliva which they 

 produce. These latter fibres very possibly terminate in the salivary 

 cells themselves. If, on the other hand, the sympathetic fibres be di- 

 yided, stimulation of the tongue by sapid substances, or of the trunk of 

 the lingual, or of the glosso-pharyngeal continues to produce a flow of 

 saliva. From these experiments it is evident that the chorda tympani 



FIG. 178. -Diagrammatic representation of submaxillary gland of the dog with its nerves and 

 blood-vessels. (This is not intended to illustrate the exact anatomical relations of the several 

 structures.) sm. gld., the submaxillary gland into the duct (sm. d.) of which a canula has been 

 tied. The sublingual gland and duct are not shown; n. 1., n. I'., the lingual or gustatory nerve; 

 ch. t., ch. t'., the chorda tympani proceeding from the facial nerve, becoming conjoined with the 

 lingual at n. I'., and afterwards diverging and passing to the gland along the duct; sm. gl., sub- 

 maxillary ganglion with its roots; n. L, the lingual nerve proceeding to the tongue; a. car., the 

 cartoid artery, two branches of which, a. sm. a. and r. sm. p. pass to the anterior and posterior 

 parts of the gland; v. sm., the anterior and posterior veins from the gland ending in v. j., the jugu- 

 lar vein; v. fsym , the conjoined vagus and sympathetic trunks; gl. cer. s, the superior-cervical 

 ganglion, two branches of which forming a plexus, a. /., over the facial artery, are distributed 

 (n. sym. sm.) along the two glandular arteries to the anterior and posterior portion of the gland. 

 The arrows indicate the direction taken by the nervous impulses; during reflex stimulations of the 

 gland they ascend to the brain by the lingual and descend by the chorda tympani. CM. Foster.) 



nerve is the principal nerve through which efferent impulses proceed from 

 the centre to excite the secretion of this gland. 



The sympathetic fibres appear to act principally as a vaso-constrictor 

 nerve; and to exalt the action of the local vaso-motor centres. The 

 .sympathetic is more powerful in this direction than the chorda. There 

 is not sufficient evidence in favor of the belief that the submaxillary 



