702 COURSE OF SWEAT FIBRES. [BOOK n. 



some of the upper (chiefly the fourth, but possibly also the 

 fifth, and sixth) dorsal nerves, pass into the thoracic sympathetic, 

 thence into the ganglion stellatum, and so join the brachial plexus 

 by the fine branches passing from the ganglion to the spinal 

 nerves. The course to the fore-foot is finally along the median 

 and ulnar nerves respectively. 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. 



