70 PHYSIOLOGY CHAP. 



ficial petrosal, and the otic ganglion, and on reaching the auriculo- 

 temporal branch of the fifth nerve penetrate into the gland. The 

 sympathetic fibres run in the cervical sympathetic to the superior 

 cervical ganglion, accompany the carotid artery, and penetrate with 

 its branches by the hilurn to the interior of the three glands. 



The nerve fibres are partly medullated, partly non-medullated. 

 Some supply the muscular sheath of the vessels, others the gland 

 cells ; the former are vasomotor, the latter secretory fibres. These 

 last, mostly as non-medullated fibres, perforate the basement 

 membrane of the acini, and terminate between the alveolar cells in 

 a free arborescence of the finest varicose fibrils (Fig. 20, B.). 

 Paladino (1872) observed direct terminations of the nerve fibres in 

 the gland cells of the salivary gland of dogs, solipeds, and man. 

 He further described intraglandular gangliated plexuses in the 

 submaxillary of the dog and of man. 



II. It is evident that the salivary secretion is directly under 

 the control of the nervous system. The mere mental image of any 

 sapid substance, the sight or smell of a favourite food, is sufficient, 

 in vulgar parlance, " to make the mouth water." Stimulation of 

 the abdominal fibres of the vagus, in nausea, incites a copious flow 

 of saliva, principally during the reflux of food from the stomach 

 to the extremity of the oesophagus, which precedes vomiting. 



To these facts of common observation which are within 'the 

 reach of all, we can add others, arrived at by physiological experi- 

 ment. The salivary secretion can also be excited by centripetal 

 stimulation of some of the sensory nerves, e.g. the central end of 

 the vagus or sciatic in a curarised dog (Owsjannikow). Electrical 

 excitation of a given area of the cerebral cortex (the so-called 

 centre for facial movements) promotes secretion (Landois, Lepine, 

 Bochefontaine), etc. It is interesting in this connection to note 

 that among the forms of partial epilepsy there is one in which the 

 fits are characterised by an enormous secretion of saliva 

 (Emminghaus). 



A remarkable contribution to the more exact knowledge of 

 reflex excitation of the salivary secretion was made by Pawlow 

 and his co-workers (1904). The extraordinary aptness of these 

 reflexes is shown by a number of experiments, the most important 

 of which may be briefly summarised : 



If some quartz pebbles are introduced into the mouth of a dog 

 with a salivary fistula, the animal, after turning them over with 

 its tongue, lets them drop out without any flow of saliva, or at 

 most a few drops only, being excited. If, on the contrary, the 

 same stones are introduced into the dog's mouth in the form of 

 powder, so that it cannot push them out with the tongue, saliva 

 at once flows freely and carries away the quartz dust. 



Dry, solid food produces an abundant secretion of saliva ; fluid 

 aliments, which already contain enough moisture for deglutition, 



