1 28 Blood Flow and Secretion 



to exert no permanent dilator action in the gland, at least in the 

 anaesthetized animal, for section of that nerve does not diminish 

 the flow of blood, even when the sympathetic constrictors are 

 intact. 



Ever since the experiment described, Claude Bernard has been 

 regarded as the discoverer of a special type of nerve fibres, the 

 vasodilators, and his experiment has belonged to the classroom 

 demonstration repertoire, to show the action of such fibres. Never- 

 theless, the presence of dilator fibres in the chorda has repeatedly 

 been questioned and is not considered as established by all inves- 

 tigators. The complicating factor is, of course, the secretion of 

 saliva which is obtained concomitantly with the vasodilatation on 

 stimulation of the chorda. It was early suggested that the vasodila- 

 tation might be secondary to the secretion, caused by metabolites 

 ^^jpossessing a vasodilator activity. 



The discovery that a vasodilatation can still be elicited when the 

 secretion has been suppressed by atropine (Heidenhain, 1872) 

 seemed to afford convincing proof of the existence of special vaso- 

 dilator fibres until the investigations of Barcroft and his co-workers 

 (Barcroft, 19 14) disclosed that stimulation of the chorda may in- 

 crease the metabolism of the gland even under these conditions. 

 Barcroft came to the conclusion that the dilatation in the submaxil- 

 lary gland of the cat which appears during or after sympathetic 

 stimulation is exclusively secondary to the secretion, a "functional 

 dilatation". It was reasonable to assume a similar mechanism at 

 work when the chorda is stimulated. Anrep and Cannan (1922) 

 found chorda stimulation to raise the blood-sugar consumption of 

 the submaxillary gland even after administration of a dose of 

 atropine which abolished the secretory response. 



Henderson and Loewi (1905) noticed that atropine diminishes 

 the dilatation caused by chorda stimulation and suggested that the 

 dilatation is in part due to some substance developed by the active 

 salivary cells. Bayliss (1923) admitted that production of metabo- 

 lites may aid in the dilatation observed during chorda stimulation 

 but maintained that specific vasodilator fibres also contribute to 

 the dilation. In support of this view he quoted Barcroft's figures in 

 which he could find no correlation between the degree of dilata- 

 tion and the increase in oxygen consumption. "Thus, a 109 per 

 cent increase in the latter coincides with a 488 per cent increase in 

 the former in one case, while, in another case, a 50 per cent 



