CHAP. I.] XERVOUS SUPPLY OF SALIVARY GLANDS. 13 



The Nervous Supply of the Salivary Glands. 



We shall not enter, in this place, into a detailed description of the 

 innervation of any one of the salivary glands, but shall confine our- 

 selves to the following categoric statements. 



Each salivary gland is supplied by at least three classes of fibres, 

 viz. secretory fibres, vaso-constrictor and vaso-dilator fibres, of which 

 the first and the third are in general conveyed to the glands in 

 branches of cerebral nerves : these are, the chorda tympani for the 

 submaxillary and sublingual ; and the auriculo-temporal (which how- 

 ever derives them through communications with the otic ganglion) 

 for the parotid. The second class, of vaso-constrictor, fibres for the 

 most part run in sympathetic trunks, which, however, also contain 

 secretory fibres. 



When therefore one of the cranial branches supplying a gland is 

 stimulated, there occur two acts, viz. secretion 1 and simultaneous 

 dilatation of blood-vessels 2 ; that these two acts are not absolutely 

 interdependent is proved by the fact that certain drugs such as 

 atropin 3 paralyse the one set of fibres, leaving the other intact. 



When, on the other hand, the sympathetic filaments supplying 

 the gland are stimulated, the blood-vessels of the gland contract, and 

 there is produced a small quantity of saliva differing in physical 

 characters and chemical composition from that obtained under the 

 circumstances first referred to. 



Heidenhain's According to Heidenhain 4 , however, in each of the 

 distinction toe- two kinds of nerves supplying a salivary gland there 

 tween secre- exist, besides the vascular nerve fibres, secretory and 



t0 *te ^erves* " tr P n * c ' or as we s ^ould prefer to term them, 'metabolic' 

 fibres, though the number of one or other of these classes 

 may be insignificant ; the secretory usually predominating in the 

 cranial nerve branches, the trophic in the sympathetic. Stimulation 

 of secretory fibres leads, according to Heidenhain, to an increased flow 

 of water ; stimulation of the metabolic to an increased secretion of 

 specific substances, in consequence of the conversion of insoluble into 

 soluble substances, and to an increased production of protoplasm. 



There are decided objections to accepting the term trophic (which has 

 already been used in a different and fairly well-known sense) to designate 

 those nerve fibres whose action it is specially to increase the metabolism 

 of secreting cells, and we shall therefore in general use metabolic in the 

 same sense as Heidenhain's expression trophic. The term trophic has 

 been generally employed to designate the action which certain nerve 



1 Ludwig, 'Neue Versuche liber die Beihiilfe der Nerven zur Speichelabsonderung.' 

 Zeitschr.f. rat. Mediz., N.F. (1851), p. 259. 



2 Claude Bernard, Comptes Eendus, 28 Jan. 1858. 



3 Kieuchel, 4 Das Atropin u. die Hemmungsnerven.' Dorpat, 1862. 



4 Heidenhain, 'Physiologic der Absonderungsvorgange.' Hermann's Handbuch, 

 Vol. v. p. 55. 



