SECRETION PHYSIOLOGY. 339 



has been made to answer this question indirectly by showing 

 that vaso-dilation may ensue without secretion, and secretion 

 without vaso-dilation. But all the evidence which has hitherto 

 been offered, that vaso-dilation may ensue without secretion, 

 and that it alone is incapable of causing secretion, is invalidated 

 by the fact that the conditions of such experiments produce an 

 abnormal gland, or capillary wall, both factors which research 

 on lymph formation have shown to be of importance. Quinine, 

 hydrochloric acid, sodium carbonate, or atropine, drugs which 

 enable vaso-dilation to ensue without secretion, probably alter 

 the permeability of the capillary, or gland cell. So that infer- 

 ences can be drawn from such experiments as to processes oc- 

 curring in the normal gland only with the greatest caution. The 

 evidence with the exception of the post-mortem secretion, that 

 the chorda may cause a secretion without vaso-dilation is also 

 unsatisfactory, as pointed out on p. 355. Attention may now be 

 directed, hence, to this post-mortem chorda secretion. 



It is probable from the considerations presented on page 338, 

 that the liquid causing this secretion is derived from the blood. 

 Can the chorda tympani act on the blood vessels in the absence 

 of circulation, in such a manner as to facilitate the passage of 

 that liquid from the capillaries to the gland cells ? The only 

 possible w^ay in which it might so act, I believe, is by causing 

 an active dilation of the capillaries or veins, as well as of the 

 arterioles. Is there any evidence that the chorda has such an 

 action ? 



Tiegerstedt*^'^^'^ states that the capillaries are contractile but that 

 they have not hitherto been shown to be under nerve control. 

 Roy and Brown have brought forward strong evidence that the 

 capillaries are normally in a state of tonic contraction and that 

 they may actively expand independent of the blood pressure. 

 They observed in the capillaries of the web of the frog's foot 

 that, although blood pressure might be diminished almost to 

 atmospheric pressure, the application for an instant of chloroform 

 to the web caused an enormous expansion of the capillaries. 

 Interesting, also, in this connection, are the observations of von 

 Frey. v. Frey^'' examined microscopically the capillaries of the 



