KIDNEY AND SKIN AS EXCRETORY ORGANS. 869 



is obvious that the organic constituents are of minor importance. 

 The main fact to be considered in the secretion of sweat is the form- 

 ation of water. 



Secretory Fibers to the Sweat Glands. Definite experimental 

 proof of the existence of sweat nerves was first obtained by Goltz * 

 in some experiments upon stimulation of the sciatic nerve in cats. 

 In the cat and dog, in which sweat glands occur on the balls of the 

 feet, the presence of sweat nerves may be demonstrated with great 

 ease. Electrical stimulation of the peripheral end of the divided 

 sciatic nerve, if sufficiently strong, will cause visible drops of sweat 

 to form on the hairless skin of the balls of the feet. When the 

 electrodes are kept at the same spot on the nerve and the stimula- 

 tion is maintained the secretion soon ceases; but this effect seems 

 to be due to a temporary injury of some kind to the nerve fibers 

 at the point of stimulation, and not to a genuine fatigue of the 

 sweat glands or the sweat fibers, since moving the electrodes to a 

 new point on the nerve farther toward the periphery calls forth a 

 new secretion. The secretion so formed is thin and limpid, and 

 has an alkaline reaction. The anatomical course of these fibers 

 has been worked out in the cat with great care by Langley. f He 

 finds that for the hind feet they leave the spinal cord chiefly in the 

 first and second lumbar nerves, enter the sympathetic chain, and 

 emerge from this as pos^ganglionic fibers in the gray rami which 

 pass from the sixth lumbar to the second sacral ganglion, but chiefly 

 in the seventh lumbar and first sacral, and then join the nerves of 

 the sciatic plexus. For the forefeet the fibers leave the spinal cord 

 in the fourth to the tenth thoracic nerves, enter the sympathetic 

 chain, pass upward to the first thoracic ganglion, whence they are 

 continued as postganglionic fibers that pass out of this ganglion by 

 the gray rami communicating with the nerves forming the brachial 

 plexus. The action of the nerve fibers upon the sweat glands can 

 not be explained as an indirect effect, for instance, as a result of 

 a variation in the blood-flow. Experiments have repeatedly shown 

 that, in the cat, stimulation of the sciatic still calls forth a secre- 

 tion after the blood has been shut off from the leg by ligation of 

 the aorta, or indeed after the leg has been amputated for as long 

 as twenty minutes. So in human beings it is known that profuse 

 sweating may often accompany a pallid skin, as in terror or 

 nausea, while, on the other hand, the flushed skin of fever is char- 

 acterized by the absence of perspiration. There seems to be no 

 doubt that the sweat nerves are genuine secretory fibers, causing 

 a secretion in consequence of a direct action on the cells of the sweat 

 glands. In accordance with this physiological fact histological 



* "Archiv f. die gesammte Physiologic," 11, 71, 1875. 

 t "Journal of Physiology," 21, 347, 1891. 



