CHAP, in.] CUTANEOUS SECRETION. 389 



be stimulated with the interrupted current, a profuse sweat may 

 readily be observed to break out in the hairless sole of the foot on 

 that side. Not only may the secretion be observed when the 

 cutaneous vessels are thrown into a state of constriction by the 

 stimulus, but it also appears when the aorta or crural artery is 

 clamped previous to the stimulation, or indeed when the leg is am- 

 putated. Moreover when atropin has been injected, the stimula- 

 tion produces no sweat, though vaso-motor effects follow as usual. 

 The analogy between the sweat-glands of the foot and such a gland 

 as the submaxillary is in fact very close, and we are justified in 

 speaking of the sciatic nerve as containing secretory fibres distri- 

 buted to the sudoriparous glands of the foot. Similar results 

 may be obtained with the nerves of the fore limb. And in our- 

 selves a copious secretion of sweat may be induced by tetanizing 

 through the skin the nerves of the limbs or the face. 



If a cat in which the sciatic nerve has been divided on one side 

 be exposed to a high temperature in a heated chamber, the limb 

 the nerve of which has been divided remains dry, while the feet of 

 the other limbs sweat freely. This result shews that the sweating 

 which is caused by exposure of the body to high temperatures is 

 brought about not by a local action on the sweat-glands but by the 

 agency of the central nervous system. A high temperature up to 

 a certain limit increases the irritability of the epithelium of the 

 sweat-glands as it does that of other forms of protoplasm : thus 

 stimulation of the sciatic in the cat produces a much more abundant 

 secretion in a limb exposed to a temperature of 35 or somewhat 

 above, than in one which has been exposed to a distinctly lower 

 temperature, and in a limb which has been placed in ice-cold 

 water hardly any secretion at all can be gained ; but apparently 

 mere rise of temperature without nerve-stimulation will not give 

 rise to a secretory activity of the glands. The sweating caused 

 by a dyspnoeic condition of blood, and such appears to be the 

 sweat of the death agony, is similarly brought about by the 

 agency of the central nervous system. When an animal with the 

 sciatic nerve divided on one side is made dyspnceic, no sweat 

 appears in the hind limb of that side, though abundance is seen in 

 the other feet. 



Sweating may be brought about as a reflex act. Thus when 

 the central stump of the divided sciatic is stimulated sweating is 

 induced in the other limbs, and in ourselves the introduction 

 of pungent substances into the mouth will frequently give rise to a 

 copious perspiration over the side of the face. We are thus led to 

 speak of sweat centres, analogous to the vaso-motor centres, as 

 existing in the central nervous system ; and as in the case of vaso- 

 motor centres, a dispute has arisen as to whether there is a 

 dominant sweat centre in the medulla oblongata or whether such 

 centres are more generally distributed over the whole of the spinal 

 cord. 



