130 Blood Flow and Secretion 



of an experiment vasodilatation could be produced by weak stimu- 

 lation of the chorda which did not cause any secretion. The 

 experiments by Chauchard and Chauchard (1929) showing a dif- 

 ferent chronaxie for the secretory and the dilator response were 

 quoted. Beznak made, in addition, some degeneration experiments 

 and found that using stimuli of low intensity it was possible to get 

 a secretion without dilatation when the chorda had been cut 3-9 

 days earlier. 



The latter observation may seem surprising, for some kind of 

 "functional dilatation" would be expected. As to the finding that 

 vasodilatation could be elicited without secretion using a low 

 intensity of stimulation this may be an analogy to the atropine 

 experiment. It is conceivable that there are secretory fibres of dif- 

 ferent excitability, that activation of a small number of fibres by a 

 weak stimulus may excite the gland cell (as shown in the electrical 

 response, by Lundberg), without causing any secretion, and that a 

 certain degree of summation, temporal or spatial, is required for 

 the secretion to start. It would be interesting to repeat these experi- 

 ments measuring the oxygen consumption of the gland at the 

 same time. In order to accept the evidence for special vasodilator 

 fibres it seems necessary to be able to elicit a pure vasodilator 

 response, without any alterations in the secretory cells. 



A possible approach might then be to try to elicit a reflex vaso- 

 dilatation in the gland (when the cervical sympathetic trunk has 

 been cut). Bayliss (19086) found that a vasodilatation could be 

 obtained in the submaxillary gland, after section of the sympathetic 

 fibres, by stimulating the central end of the contralateral vagus. 

 However, this cannot be used as an argument in the present dis- 

 cussion, since a secretion of saliva was sometimes obtained as well. 

 Furthermore, Barcroft (19 14) found that in those experiments in 

 which he was able to obtain this reflex, there was at the same time 

 an increase in the oxygen consumption of the gland. On the whole 

 it seems improbable that it would be possible to elicit a reflex 

 vasodilatation via the chorda without stimulating the gland cells 

 even if vasodilator fibres do exist in it ; for it is generally agreed 

 that the function of parasympathetic vasodilators is to meet the 

 local need for blood rather than to participate in general circula- 

 tory adjustments. The intimate connection between secretory and 

 vasodilator fibres was illustrated in an investigation by Corbin, 

 Harrison and Wigginton ( 1 94 1 ). These authors studied the "pseudo- 



