CHAPTER VII 

 BLOOD FLOW AND SECRETION 



The intimate relationship between the supply of blood and the 

 production of saliva will be the subject of the present chapter. The 

 following examples may serve as illustrations of the problem. 

 Stimulation of the chorda tympani in cats and dogs causes a lively 

 secretion and a vasodilatation in the submaxillary gland. Stimula- 

 tion of the sympathetic of dogs causes a scanty flow of saliva from 

 this gland, richer in organic material than chorda saliva. The pre- 

 dominant vascular response is constriction. In cats, on the other 

 hand, there is usually an abundant flow of saliva, more dilute than 

 chorda saliva, and vasodilatation replaces or alternates with con- 

 striction. Is the secretory activity during chorda stimulation re- 

 sponsible for the intense vasodilatation, or is it the excitation of 

 vasodilator fibres, simultaneously with the secretory fibres, which 

 makes the rapid, steady flow of saliva possible? Are the vasomotor 

 fibres of the dog's sympathetic exclusively constrictors, which by 

 an intense action prevent the secretion of anything but a small 

 amount of concentrated saliva, and is the lively secretion of dilute 

 saliva in cats rendered possible by the existence of specific vaso- 

 dilator fibres in the sympathetic; or is the secretory innervation 

 more extensive in the cat's gland than in the dog's, and is there- 

 fore a vasodilatation, secondary to the secretion, more marked in 

 the former species? 



Generally it may be said that differences in composition and 

 amount of parasympathetic and sympathetic saliva cannot be due 

 solely to vascular factors. On the contrary, it seems highly prob- 

 able that even the single salivary cell can deliver samples of saliva 

 of different composition according to the nature of the transmitter 

 acting upon it, and with the same supply of blood. There is, on 

 the other hand, no doubt that variations in the flow of blood may 

 affect the rate of secretion and the chemical composition of the 

 saliva obtained. The amount of blood available is judged either 

 from the arterial inflow into the gland or, more often, from the 

 venous outflow. It would, of course, be more important to know 

 the quantities of blood placed at the disposal of the different 



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