258 DIGESTION 



auriculo-temporal branch of the fifth nerve through the nerve of Jacobson, the 

 small superficial petrosal, and the otic ganglion. 



The sympathetic fibers run in the cervical sympathetic trunk to the superior 

 cervical ganglion, and from there follow the blood vessels to the hilus of the 

 appropriate gland. 



Ganglion cells are interpolated in the course of these nerves those of the 

 sympathetic fibers for the sublingual and submaxillary being located in the supe- 

 rior cervical ganglion. The ganglion cells of the cerebral secretory fibers for 

 the sublingual gland are distributed as small ganglia over the entire gland (to 

 these belong also the sublingual ganglion) ; those for the submaxillary lie for 

 the most part in the hilus of the gland itself (Langley). 



On stimulation the different secretory nerves give different results, which 

 vary with the species of animal experimented upon. We shall consider here 

 only the results obtained in the dog. 



Stimulation of the cerebral fibers to any of the glands causes almost imme- 

 diately a copious secretion of a fluid poor in solids,, which may continue for 

 hours, if the stimulation be maintained at the proper strength. The secre- 

 tion produced from the submaxillary by excitation of the sympathetic appears 

 later. At first a few drops of a fluid rich in solids come from the duct, then 

 the secretion ceases, but reappears on continued stimulation. The parotid 

 as a rule gives no secretion on stimulation of the sympathetic, probably 

 because the thick fluid stops up the duct. 



Since stimulation of the cerebral fibers causes a considerable dilatation of 

 the blood vessels of the gland and a consequent increase of blood flow (as much 

 as six times the original) (cf. page 234), whereas stimulation of the sympathetic 

 causes vasocontraction and a considerable decrease of blood flow, it might be 

 thought that the difference in the secretion in the two cases is due to the differ- 

 ence in the amount of blood supplied. But this is not true. For if the arteries 

 of the gland be entirely closed off and the cerebral fibers be then stimulated, the 

 quantity of secretion obtained is smaller, but it has all the properties of the nor- 

 mal cerebral saliva and its percentage content of solids is not greater than when 

 the circulation is unhindered. 



Heidenhain, with some reservation it is true, has sought to explain these 

 phenomena as follows. He supposes that every gland is provided with two kinds 

 of nerve fibers: (1) those which preside over the transudation of water and of 

 the salts, the " secretory fibers," and (2) those which control the formation of the 

 soluble constituents and the growth of the protoplasm, the " trophic fibers." 

 These fibers occur in the different nerves of the glands in different numbers. 

 Thus the cerebral fibers in the dog would be relatively poor in trophic but rela- 

 tively rich in secretory fibers, while the sympathetic would contain only a few 

 secretory but many trophic fibers. 



It is not to be denied that Heidenhain has brought many facts to the support 

 of this view. For example, simultaneous stimulation of the sympathetic and 

 the glossopharyngeal in the dog increases considerably the percentage composi- 

 tion of solids in the parotid saliva. But it is not possible to explain all the 

 known facts concerning the influence of nerves on the salivary secretion from 

 this point of view. Thus if the glands be poisoned, not too severely, with atropine, 

 stimulation of the chorda is entirely without effect at a time when stimulation 

 of the sympathetic is still effective. Now it is very probable that atropine acts 

 so as to paralyze the end organs of the cerebral fibers, and from the fact just 



