Active Hyperemia. 



403 



during muscular activity. We must consequently expect to find other 

 functions for the vaso-dilator nerves. 



7. Control of Body Temperature. 



The fortunate employment of the dog gave the clue to a possible function 

 of the vaso-dilator fibres in the lingual nerve. It is a common fact that dogs 

 resort to panting and extrusion of the tongue for cooling of the blood. The 

 effect upon the blood-flow in the tongue resulting from the stimulation of the 

 heat receptors in the skin was therefore studied. 



The fur was cut off, a radiant-heat hemi-cylinder was placed over the trunk 

 of the animal, the venous outflow from the lingual vein recorded, and the 

 rectal temperature observed throughout the experiment. 



The warming of the skin caused hyperemia and increased lingual blood- 

 flow long before the body temperature was appreciably raised (fig. 21, i and ii). 

 In all cases where this response did not occur the body temperature steadily 

 advanced; Stewart (1913) also emphasises the importance of reduced blood- 

 flow in fever. 



To test whether this was an effect of heated blood directly upon the vessels 

 or a reflex mechanism, the lingual nerves were cut on both sides and time 

 given for the effect of this stimulus (fig. 7) to pass off. The application of 

 radiant heat to the skin of the trunk was now not followed by lingual 

 hyperemia (fig. 21, iii and iv). 



I 



k 1 



lllllHlllllllilllllillllinii 



mmwmm 















Lino.nvs.cut 

 — ii ii 1 1 ii i i ii in i in 



HiHuiiirnni/ijii 





ifllflllrliJIIIIJJI 



Heat 







■ 



Fig. 21. 



The same results were obtained in another dog, which was immersed in a 

 warm bath. It is thus apparent that a nervous reflex of this nature brings 

 about a quicker response than could be obtained by the heating up of the 

 whole blood ; and, further, the nervous reflex ensures vaso-dilation of that 

 particular organ which is most favourably disposed for the cooling of the 

 blood, whereas heated blood would have a generalised effect on external and 

 internal organs alike. It is possible that the flushing of the face in man in 

 emotional states and in fever may also be accounted for by similar reflexes 



