492 THE SALIVAR Y GLANDS. 



is less copious than that obtained by placing acids in the mouth, and it 

 is more copious on the side stimulated than on the opposite side. 



A special relation has also been said to exist between the state of 

 the mucous membrane of the stomach and the secretion of saliva. Thus 

 it has been said that a secretion of saliva is induced by the contact of 

 various substances with the gastric mucous membrane. 1 This, however, 

 is not satisfactorily proved. Braun 2 observed a dog, in which a gastric 

 fistula had been established, and a cannula placed in Wharton's duct. 

 No secretion of saliva was caused by introducing into the stomach, 

 flesh, acetic acid, ether, nor by irritating the mucous membrane with a 

 sponge. 



Stimulation of the central end of the vagus has rather variable 

 results on the submaxillary secretion, of the dog. It usually causes 

 secretion after a long latent period, and the secretion may continue for 

 some time after the cessation of the stimulus. Oehl 3 obtained secretion 

 although the stimulation caused no vomiting or arrest of respiration ; the 

 secretion occurred from both glands, but was greater on the side stimu- 

 lated. Buff, as a rule, only obtained secretion when there was some 

 body movement. 



Bernard noticed that a flow of saliva may be obtained by stimulating 

 the sciatic 4 and various other sensory nerves ; it may, indeed, be obtained 

 by stimulating any sensory nerve in the body. This reflex secretion is 

 abolished by deep anaesthesia ; whether it ceases coincidently with the 

 production of anaesthesia is, however, uncertain. According to Buff, 5 

 the secretion does not occur in uncurarised animals, unless the stimulus 

 produces also a reflex body movement. 



The gustatory reflex secretion is caused wholly by impulses passing 

 down the cranial secretory nerves. But a secretion may, in certain 

 circumstances, be caused by impulses passing along the sympathetic 

 nerve ; for example, when the central end of a sensory nerve is stimu- 

 lated, the secretion, so far as is known, is always accompanied by a con- 

 striction of the blood vessels of the gland. 



In man, cases sometimes occur in which there is a permanent absence 

 of secretion from the large salivary glands, and from the glands of the 

 mucous membrane of the mouth. Such cases are rarer in men than in 

 women. In women the loss of secretory power usually comes on after 

 middle life, and may be the result of an emotional shock. For some 

 time pilocarpine will still cause a secretion of saliva (Hadden), but 

 eventually it causes none, though it still causes sweating. 6 The 

 absence of secretion is no doubt due to a derangement of the reflex 

 nervous mechanism, so that impulses passing up the afferent nerves no 

 longer give rise to efferent impulses. The lack of normal functional 

 activity probably causes a gradual atrophy of the glands, and a diminu- 

 tion of irritability of the nervous and glandular structures, so that 

 eventually pilocarpine or the amount of it which can be given safely 

 no longer produces a flow of saliva. 



1 For an account of papers on the reflex secretion of saliva, cf. Buff, Beitr. z. Anat. u. 

 PhysioL (Eckhard), Giessen, 1888, Bd. xii. S. 3. 

 * Ibid., 1876, Bd. vii. S. 44. 



3 Compt. rend. Acad. d. sc., Paris, 1864, tome ix. p. 336. Secretion on stimulation of 

 the central end of the vagus was first observed by Bernard, 1859. 



4 Cf. also Owsjannikow and Tschiriew, Melanges biol. Acad. imp. d. sc. de St.-Peters- 

 bourg, 1872, tome viii. p. 651. 



5 Op. cit. 6 Hutchinson, cf. Hadden, Brain, London, 1889, vol. xi. p. 484. 



