THE REGULATION OF SALIVARY SECRETION. 179 



length of time during which the flow of saliva can be kept 

 up under these circumstances is appreciably less than when a 

 weaker current is used. In a properly arranged experiment 

 with a moderate current a flow of saliva may be maintained 

 an hour or more. 



The submaxillary of the dog may secrete in five minutes 

 an amount of saliva equal to its own weight, and by alter- 

 nately stimulating and resting the gland 250 c.c. may be 

 obtained in 10 to 12 hours. Toward the end of this time 

 the rate of flow is less than at the beginning of the experi- 

 ment. 1 



Some difference exists in the amount and in the character 

 of the saliva as obtained from the different glands in different 

 animals. In the dog stimulation of the auriculo-temporal 

 nerve supplying the parotid by methods similar to those just 

 described yields from one-half to two-thirds the amount of 

 saliva obtained from the submaxillary gland. This agrees 

 with CLAUDE BERNARD'S finding that when saliva is obtained 

 reflexly from the dog the submaxillary gland furnishes twice 

 as much as the parotid and ten times as much as the sub- 

 lingual gland. 



While the composition of the saliva as obtained from the 

 different glands when their cranial nerves are stimulated is 

 not the same (the submaxillary saliva, for example, always 

 contains more organic matter than either the sublingual or 

 parotid, and the sublingual more salts than either of the other 

 two) , still it is in all cases clear, thin, and watery, and contains 

 only from 1 to 2 percent of solid matter. 



Exposure, section, and stimulation of the sympathetic 

 fibres going to one of the salivary glands is followed by quite 

 a different effect. In this case also a flow of saliva is ob- 

 tained, only much less than when the corresponding cranial 

 nerve is stimulated, and the saliva has entirely different 

 characteristics. While histological study may show that a 



1 LANGLEY: Schaefer's Text-book of Physiology, 1900, Vol. I, p. 493. 



