Parasympathetic Vasodilators 129 



increase coincides with an increase in rate of blood flow in 812 per 

 cent; that is, larger dilatation with a less consumption of oxygen." 

 Recently Stromblad (1959) has, like Barcroft, found an increased 

 oxygen consumption on stimulation of the chorda when the secre- 

 tory response had been entirely prevented by atropine ; there was 

 no positive correlation between this increase and the increase in 

 blood flow. 



As a further argument suggesting that the chorda may supply 

 the gland with vasodilator fibres, Bayliss pointed out that stimu- 

 lation of the chorda causes a vasodilatation in the tongue even if the 

 oxygen consumption is not increased (Anrep and Evans, 1920). 



Dale and Gaddum (1930) accepted the view that the chorda 

 contains vasodilators both for the tongue and the submaxillary 

 gland and concluded that these fibres are cholinergic. Experiments 

 by Bain (1933, 1936) and by Feldberg (1933) showed that acetyl- 

 choline is released in the tongue on stimulation of the chorda 

 fibres. The fact that the dilatation in the gland, contrary to the 

 secretion, was not abolished by atropine, whereas both actions 

 elicited by injected acetylcholine were abolished, was supposed by 

 Dale and Gaddum to be due to a release of the acetylcholine at the 

 vasodilator endings in such great "intimacy with the receptive 

 mechanism that atropine cannot prevent its access thereto". 



In their investigations on the chemical transmission in the sub- 

 maxillary gland Henderson and Roepke (1933) suggested another 

 mode in which the vasodilatation could be secondary to activity in 

 the secretory nerves. They found chorda stimulation to cause a 

 release of acetylcholine even in the presence of atropine and 

 pointed out that the vasodilatation obtained might be due to the 

 transmitter diffusing from the terminals of the secretory fibres. In 

 view of the fact that atropine abolishes the dilator effect of injected 

 acetylcholine, this explanation seems rather unlikely. 



On the other hand, Beznak (1934) who, likewise, demonstrated 

 the release of acetylcholine in the submaxillary gland when the 

 chorda was stimulated, postulated the existence of cholinergic 

 vasodilator fibres and raised the question whether the secretion 

 might be evoked by acetylcholine from the vasodilators. He came, 

 however, to the conclusion that there are separate secretory and 

 vasodilator fibres in the chorda. This view was based on the 

 observation that secretion and dilatation could be elicited inde- 

 pendently in the submaxillary gland of the dog. In the beginning 



P.S.G. — K 



