SYMPATHETIC FIBRES TO THE SKIN. 625 



with the inadequacy of detailed experiment on the course taken by the 

 post-ganglionic fibres, makes it obvious that the scheme just memtioned 

 is only to be regarded as approximate and provisional. 



SYMPATHETIC FIBRES TO THE SKIN, EXCEPT THAT OF THE HEAD AND 

 OF THE ANO-GENITAL EEGION. 



Effects produced by stimulation. The actions set going in the 

 skin by the sympathetic nerves, naturally vary in different parts and in 

 different animals, in accordance with the kind of structures which have 

 developed in them. Thus, in rabbits, the only action produced in the 

 skin of the trunk and limbs is a vasomotor one. Sweat glands and 

 erector muscles for the hairs are absent. The effects which can be 

 produced in the skin by stimulation of some part or other of the 

 sympathetic chain are as follows, omitting the effects produced on the 

 skin of the genital region, which will be given in the account of the 

 external generative organs : 



1. Contraction of the arteries. This can be brought about in all parts 

 of the skin, but apparently more easily in some parts than in others. 

 Thus, with equal nervous stimulation, it is said that there is greater 

 contraction in the vessels of the foot than in the vessels of the thigh. 

 The sympathetic fibres have not been shown to cause directly any 

 change in the capillaries. They have been found to cause contraction 

 in the veins of the wing of the bat, 1 and in the superficial veins of the 

 leg of the cat and rabbit. 2 The former have rhythmic contractions and 

 dilatations, like those which occur in the arteries of the ear of the rabbit ; 

 the rhythm depends upon impulses passing from the spinal cord. 



2. Secretion from sweat glands. Observations on the distribution of 

 secretory fibres to the sweat glands of the skin, other than that of the 

 head, have only been made upon the cat and dog ; and in the cat and 

 dog the glands only occur on the pads of the feet. 



3. Erection of hairs. This is also a local occurrence. In the cat it 

 occurs in the dorsal strip of skin which is innervated by the posterior 

 cutaneous branches of the spinal nerves, and in the tail. In the dog 

 and ape the hairs are affected in a similar dorsal strip. In the hedgehog 

 the region in which quills are moved is co-extensive with the region in 

 which quills are found, so that here the sympathetic causes movement 

 in the region of the lateral cutaneous as well as in that of the posterior 

 cutaneous skin branches. 



The " goose skin " which occurs in man is a similar phenomenon, and 

 is no doubt also produced by sympathetic nerve fibres. 



We may note here that the action of the sympathetic chain is 

 unilateral on the trunk ; it is unilateral also on the limbs, except for an 

 occasional very trifling effect on the opposite hind-limb, but it is 

 bilateral on the tail and on the external generative organs, though 

 generally stronger on the same side. The bilateral action is connected 

 with the fact that the vertebral ganglia from the second sacral, and 

 sometimes from the first sacral downwards, are connected together on 

 the two sides, and it is these ganglia, as we shall see, which send fibres 

 to the tail and to the external generative organs. 



1 Cf. Wharton Jones, Arch, de physiol. norm, et path., Paris, 1849 ; Schiff, Arch. f. d. 

 ges. Physiol., Bonn, 1881, Bd. xxvi. S. 456. 



- Bancroft, Am. Jmtrn. Physiol., Boston, 1898, vol. i. p. 477. 

 VOL. II. 40 



