640 SYMPATHETIC AND OTHER SYSTEMS OF NERVES. 



Vasoconstrictor fibres. — According to Griitzner and Heidenhain, 1 

 the abdominal sympathetic trunk in the dog contains vaso-constrictor 

 fibres for the muscles of the limb. They found that stimulation of the 

 abdominal sympathetic trunk causes a slight fall of temperature in the 

 gastrocnemius, and a fall of blood pressure in the veins carrying blood 

 from the extensor group of muscles of the thigh. 



Gaskell 2 observed directly the blood-flow from the extensor group 

 of muscles of the thigh ; he obtained a slight, but only a slight, decrease 

 of blood-flow on stimulating the abdominal sympathetic. The result 

 is not convincing as to the presence of vasomotor fibres, since Gaskell 

 obtained only a transient increase of blood-flow by section of the 

 sympathetic, and no decrease by stimulating the fifth lumbar grey 

 ramus. I have not seen any change of colour in the muscles of the 

 limbs in the cat and rabbit, on stimulation of the abdominal sympathetic, 

 though sometimes there appeared to be a slight constriction of the 

 larger arteries. We may conclude that, if there is a sympathetic vaso- 

 constrictor supply for the muscles of the limbs, it is at any rate not well 

 developed. 



The circulation in some of the small muscles of the eye and of the 

 larynx can be examined under the microscope. On stimulation of the cervical 

 sympathetic, I have not found any certain change in the size of the small 

 arteries of the muscle ; sometimes there was a slight slowing in the blood-flow 

 in the capillaries, suggesting a contraction of some larger arteries outside the 

 muscle. 



Vaso- dilator fibres. — The presence of vaso-dilator fibres in the nerves 

 supplying the muscles of the limb has been advocated by Gaskell, 3 and 

 by Heidenhain with his collaborators. 4 Gaskell did not deal with the 

 origin of these fibres. Heidenhain considered that they ran to the 

 muscular nerves from the abdominal sympathetic. 



We are here only concerned with the question of vaso-dilator fibres 

 of sympathetic origin, but as there is some ground for believing that if 

 vaso-dilator fibres are present in the muscular nerves they arise from 

 the sympathetic, it is advisable to mention, though briefly, the chief 

 experiments which have been brought forward to show that the muscles 

 receive vaso-dilator fibres. 



Gaskell observed the rate of blood-flow from the extensor muscles 

 of the thigh of the dog on stimulation of the crural nerve. Normally, 

 this caused great increase of blood-flow, after a preliminary decrease. 

 When curari was given in minimal amount, just sufficient to paralyse 

 the motor nerves to the muscle, an increase in the blood-flow was 

 sometimes obtained on stimulating the crural. When a larger dose 

 of curari was given, the crural became ineffective. 



Now, the amount of curari which paralyses the vaso-dilator action of 

 the crural does not paralyse any known vaso-dilator nerve fibres, neither 

 those of the chorda tympani, nor of the nervus erigens, nor of the dog's 

 cervical sympathetic. In other words, the vaso-dilator fibres of muscle, 



1 Arch./, d. gcs. Physiol., Bonn, 1878, Bd. xvi. S. 1. 



2 Journ. Physiol., Cambridge and London, 1878, vol. i. p. 108. 



3 Arb. a. d. physiol. Anst. zu Leipzig, 1876 (reprinted with slight additions in Jottm. 

 Anat. and Physiol., London, 1877, vol. xi. p. 360) ; Journ. Physiol., Cambridge and 

 London, 1878, vol. i. p. 262. 



4 Griitzner and Heidenhain, Arch. f. d. ges. Physiol., Bonn, 1878, Bd. xvi. S. 1 ; 

 Heidenhain, Alexander u. Gottstein, ibid., S. 31. 



