DIGESTION 305 



fibres to the submaxillary gland having theirs in a little 

 ganglion at the hiliis of the gland (S.M.). This was demon- 

 strated by painting the two ganglia with nicotine (p. 198). 

 When applied to the submaxillary ganglion, the drug does 

 not interfere with the passage of impulses to the submaxillary 

 gland, but stops those going to the sublingual. 



If the duct of the gland be connected with a mercurial 

 manometer, it is found that, when the chorda tympani is 

 stimulated, the pressure of secretion may exceed the blood 

 pressure in the carotid, showing that the saliva is not formed 

 by filtration. 



(2) When the perivascular sympathetics, or when the 

 sympathetic cord of the neck is stimulated, the blood-vessels 

 of the gland constrict, and a flow of very viscous saliva 

 takes place. 



Some time after section of the chorda tympani nerve an 

 increased flow of saliva has been observed, It may be due to 

 the uncontrolled action of the peripheral nervous mechanism. 



(6) On the parotid gland (1) the auriculo-temporal nerve 

 {Aur.T.) acts in the same way as the chorda tympani acts 

 on the other salivary glands. But stimulation of the fifth 

 nerve above the otic ganglion, from which the auriculo- 

 temporal takes origin, fails to produce any effect. On the 

 other hand, stimulation of the glossopharyngeal nerve (IX.) 

 as it comes off from the brain, acts upon the parotid gland, 

 Since the glossopharyngeal is united by Jacohsons nerve 

 (J.N.) to the small superficial petrosal which passes to the 

 otic ganglion, it is obvious that the parotid fibres take this 

 somewhat roundabout course (fig. 149). 



(2) When the sympathetic fibres to the gland alone are 

 stimulated, constriction of the blood-vessels but no flow of 

 saliva occurs ; but if, when the flow of watery saliva is being 

 produced by stimulating the glossopharyngeal or Jacobson's 

 nerve, the sympathetic fibres are stimulated, the amount 

 of organic solids in the parotid saliva is very markedly 

 increased. 



The nerve fibres passing to the salivary glands are pre- 

 sided over by groups of cells, the Salivary Centre, in the 

 medulla oblongata which may be stimulated reflexly or 

 20 



