340 MATHEWS. 



frog's tongue. He found that on stimulation of the dilator, 

 hypoglossal nerve, a dilation of the capillaries ensued even after 

 the blood supply had been cut off If the artery be clamped, 

 he observed that the blood streamed out of the capillaries both 

 into the arteries and veins. If, now, the hypoglossal be stimu- 

 lated the capillaries dilate and blood streams into them from the 

 arterioles and veins. This movement persisted for from one to 

 two minutes after clamping the artery. Furthermore, in ex- 

 perimenting on the blood flow from the veins of the submaxil- 

 lary gland of the dog during stimulation of the chorda, v. Frey 

 often observed that stimulation of the chorda was followed by a 

 temporary decrease in the rate of flow of blood from the vein, 

 before the ordinary increase. He suggests that this would seem 

 to indicate a widening of the capillary area leading to a back 

 flow of blood from the veins were it not more probable that the 

 increased flow from the dilated arterioles would be more than 

 sufficient to offset this. 



These facts justify the conclusion, I believe, that on stimu- 

 lating the chorda tympani in the severed head, the capillaries of 

 the gland probably dilate, and that blood enters them from the 

 veins. 



How such a vaso-dilation might lead to a secretion is not 

 clear, but two possibilities suggest themselves : (i) that the 

 capillaries are thus brought into closer relation with the alveoli, 

 and the constant attraction exerted by the gland contents for 

 the water of the blood is thus rendered effective ; or (2) that 

 vaso-dilation may in some way increase the permeability of the 

 capillary wall. The post-mortem chorda secretion can not, I 

 believe, be accepted unconditionally as illustrative of a secre- 

 tion independent of vaso-dilation, until these possibilities have 

 been shown to be non-existent, or non-essential. 



If it shall be found that vaso-dilation of itself is a cause of 

 secretion in the normal gland, and that the gland cell is not the 

 secretory agent, the facts of secretion in the submaxillary gland 

 will probably necessitate the following conclusions, which are 

 not without interest for those studying the physiology of the 

 circulation: (i) That stimulation of the chorda causes an ac- 



