478 SALIVA [CH. XXX. 



secretory, the latter being paralysed by atropine. The chorda tympani 

 nerve is, however, the principal nerve through which efferent impulses 

 proceed from the central nervous system to excite the secretion of 

 these glands. 



The function of the ganglia has been made out by Langley by the 

 nicotine method (see p. 302). At one time the submaxillary ganglion 

 was supposed to be the seat of reflex action for the secretion. This, 

 however, is not the case. The ganglia are cell-stations on the course 

 of the fibres to the submaxillary and sublingual glands. Nicotine 

 applied locally has the power of paralysing nerve-cells, but not nerve- 

 fibres. If the submaxillary ganglion is painted with nicotine, and 

 the nerve stimulated on the central side of the ganglion, secretion 

 from the submaxillary gland continues, but that from the sublingual 

 gland ceases. The paralysed nerve-cells in the ganglion act as blocks 

 to the propagation of the impulse, not to the submaxillary, but to the 

 sublingual gland. The cell station for the submaxillary fibres is in 

 Langley's ganglion. 



Parotid Gland. This gland also receives two sets of nerve-fibres 

 analogous to those we have studied in connection with the submaxil- 

 lary gland. The principal secretory nerve-fibres are glosso-pharyngeal 

 in origin; the sympathetic is mainly vaso-constrictor, but in some 

 animals does contain a few secretory fibres also. 



When secretory nerves are stimulated, the main result is secretion 

 leading to a diminution of the granules in the cells. The accompany- 

 ing vascular condition determines the quantity of saliva secreted. 

 Electrical changes also accompany secretory activity (see p. 473). A 

 rise of temperature is stated to occur, but if this is the case it is 

 very slight, and many observers have not been able to detect it. 



Reflex Secretion. Under ordinary circumstances the secretion 

 of saliva is a reflex action. The principal afferent nerves are those of 

 taste ; but the smell or sight of food will also cause " the mouth to 

 water " ; and under certain circumstances, as before vomiting, irrita- 

 tion of the stomach has a similar effect. These sensory nerves stimu- 

 late a centre in the medulla from which efferent secretory impulses 

 are reflected along the secretory nerves (chorda tympani, etc.) to the 

 glands. 



Pawlow has made some interesting observations on the salivary 

 glands. He made an external fistula of the submaxillary duct in the 

 dog, and found that the sight of food, the smell of food, or the 

 administration of any kind of food, caused secretion; acid or even 

 sand introduced into the mouth produced a similar effect. By means 

 of similar experiments on the parotid secretion, very different results 

 were obtained. If the dog was shown meat, or the meat was given 

 to it to eat, .there was practically no secretion. If, however, the meat 

 was given as a dry powder, a copious secretion followed ; dry bread 



