FOOD AND DIGESTION 347 



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

 strated by painting the two ganglia with nicotine (p. 154). 

 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. 



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. 



On the parotid gland 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, stimula- 

 tion of the glossopharyngeal nerve (IX.) as it comes off from 

 the brain, acts upon the parotid gland. Since the glosso- 

 pharyngeal is united by Jacobson's nerve (J.N.) to the small 

 superficial petrosal which passes to the otic ganglion, it is 

 obvious that the parotid fibres take this somewhat round- 

 about course. 



When the sympathetic fibres to the gland alone are stim- 

 ulated, 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 presided 

 over by a centre in the medulla oblongata which acts refiexly. 

 So long as this is intact, stimulation of the lingual or glosso- 

 pharyngeal leads to a reflex flow of saliva. Other nerves 

 may also act on this centre. Thus, gastric irritation, when it 

 produces vomiting, causes a reflex stimulation of salivary 

 secretion. 



According to the investigations of Pavlov the salivary glands 

 react appropriately to different kinds of stimuli through their 

 nervous mechanism. When sand or bitter or saline substances 



