96 THE INVOL UNTAR Y NER VO US S YSTEM 



Strieker pointed out in 1876 that stimulation of the peripheral 

 end of the posterior roots of the nerves, which help to form 

 the sciatic nerve, cause a marked reddening and rise of temperature 

 in the foot. 



This was confirmed by Gartner, and has been further in- 

 vestigated by Bayliss, who found, upon stimulation of the pos- 

 terior roots of the fifth, sixth, and seventh lumbar nerves and of 

 the first sacral nerve, not only a reddening of the skin and a rise of 

 temperature in the toes, but also an increased volume of the 

 lower limb, as shown by the plethysmographic method. No 

 special method of stimulation was necessary, mechanical or elec- 

 trical stimulation were both effective, pinching especially so. 

 The fibres which produce the effect do not pass into the ab- 

 dominal chain of the sympathetic, but go direct to the limb. 

 Their trophic centres are in the posterior root ganglion, as is 

 shown by the persistence of the effect after section of the posterior 

 root between the ganglia and cord, and its removal after extirpa- 

 tion of the ganglion. Bayliss comes to the conclusion that this 

 vascular dilatation is brought about by the stimulation of or- 

 dinary sensory nerve fibres acting anti-dromically. The blood 

 vessels in question are not those which supply muscles, but 

 are cutaneous vessels, for when the ankles and foot only are put 

 into the plethysmograph the effect is very large, and when the 

 skin is removed the effect is gone. 



These observations make it still more difficult to come to any 

 conclusion upon the nature of vaso-dilator nerves. It does not 

 seem possible simply to substitute sensory nerves of the skin for 

 vaso-dilator nerves in the explanation of the experiments of 

 Goltz, Luchsinger, etc. ; for not only do Bradford's experiments 

 in the kidney show that the slow rhythmical stimulation of nerves, 

 which are not sensory, will cause vascular dilatation, but Ellis 

 has shown that the slow rhythmical stimulation of the sciatic in 

 the frog causes dilatation in the web, while Oinuma working 

 with Langley found no trace of either dilatation or constriction 

 on stimulation of the posterior roots belonging to the sciatic. 



Perhaps the safest way of looking at the matter in our present 

 state of knowledge is to hold that vascular dilatation of an organ 

 can take place in two ways, either by alterations in the chemical 

 constitution of the fluids bathing the muscles of the small arteries, 

 or by the stimulation of nerve fibres which relax those muscles ; 



