SECRETION. 259 



to be mixed with the sebaceous secretion. Normally it is a very thin secre- 

 tion of low specific gravity (1004) and an alkaline reaction, although when 

 first secreted the reaction may be acid owing to admixture with the sebaceous 

 material. The larger part of the inorganic salts consists of sodium chloride. 

 Small quantities of the alkaline sulphates and phosphates arc also present. The 

 organic constituents, though present in mere traces, are quite varied in num- 

 ber. Urea, uric acid, creatinin, aromatic oxy- acids, ethereal sulphates of 

 phenol and skatol, and albumin, are said to occur when the sweating is pro- 

 fuse. Argutinsky has shown that after the action of vapor-baths, and as the 

 result of muscular work, the amount of urea eliminated in this secretion may 

 be considerable (see p. 360). Under pathological conditions involving a 

 diminished elimination of urea through the kidneys it has been observed that 

 the amount found in the sweat is markedly increased, so that crystals of it 

 may be deposited upon the skin. Under perfectly normal conditions, how- 

 ever, it is obvious that the organic constituents are of minor importance. The 

 main fact to be considered in the secretion of sweat is the formation of water. 

 Secretory Fibres to the Sweat-glands. — Definite experimental proof of the 

 existence of sweat-nerves was first obtained by Goltz l in some experiments 

 upou 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 elec- 

 trodes are kept at the same spot on the nerve and the stimulation is maintained 

 the secretion soon ceases, but this effect seems to be due to a temporary injury 

 of some kind to the nerve-fibres at the point of stimulation, and not to a 

 genuiue fatigue of the sweat-glands or the sweat-fibres, since moving the elec- 

 trodes 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 a marked 

 alkaline reaction. The anatomical course of these fibres has been worked out 

 in the cat with great care by Langley. 2 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 non-medullated fibres in the gray 

 rami proceeding 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 fore feet the fibres 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 non-medullated 

 fibres thai pass out of this ganglion by the gray rami communicating with 

 the nerves forming the brachial plexus. The action of the nerve-fibres upon 

 the sweat-glands cannot 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 secretion after the 



1 Archiv fur die gesammte Physiologic, 1875, Bd. \i. B. 71. 



2 Journal of Physiology, 1891, vol. xii. p. 347. 



