736 COURSE OF SWEAT-FIBRES. [BOOK n. 



fibres are connected with nerve-cells in these ganglia, the fibres in 

 a grey ramus starting from cells in the ganglion from which the 

 ramus issues, a few perhaps from cells in the ganglion above. In 

 the same animal, the sweat-fibres for the fore-feet leave the spinal 

 cord by the anterior roots of the sixth, seventh, and eighth thoracic 

 nerves, but also, to a less extent, by the nerves above and below. 

 Passing into the sympathetic chain, they ascend to the ganglion 

 stellatum, with the nerve-cells of which alone they are connected, 

 and by the branches of this ganglion reach the brachial plexus 

 and so the median and ulnar nerves. The course of the sweat- 

 fibres in other animals is probably very similar to the above. In 

 the horse the sweat-fibres for the side of face and in the pig those 

 for the snout appear to run in branches of the fifth nerve and not 

 in the facial; in the latter animal at least some of these fibres 

 reach the fifth nerve from the cervical sympathetic, but apparently 

 not all. 



443. The fact mentioned above that in the horse, after 

 section of the cervical sympathetic nerve on one side of the neck, 

 profuse sweating is apt to break out on that side of the face, has 

 suggested the idea that this nerve conveys inhibitory impulses to 

 the sweat-glands of the head and face, and that when it is divided 

 the sweat-fibres running in the fifth nerve, having nothing to 

 counteract them, set up sweating. But it is probably sufficient 

 in this case to suppose that the glands predisposed to activity 

 by the higher temperature brought about by the section of the 

 sympathetic dilating the blood vessels, are more easily excited by 

 any stimulus working upon them through the fifth nerve. And 

 though the idea of a double nervous mechanism, .augmenting 

 and inhibitory, governing the activity of the sweat-glands, is a 

 tempting one, there are at present no satisfactory reasons for 

 adopting it. 



