3o8 A MANUAL OF VETERINARY PHYSIOLOGY 



skin is acting freely less water passes by the kidney, and vice 

 versa. 



Sweat obtained from the horse is always strongly alkaline ; 

 after filtration it is the colour of sherry, which is probably 

 accidental, and due to contamination with dandruff. The latter 

 contains a pigment, chlorophyll. Sweat possesses a peculiar 

 horse-like odour, and has a specific gravity of 1020. We found 

 it to have the following composition :* 



Containing — 



Water - - 94*38 



( Serum albumin - - 0105 

 Organic matters 0*52 -j ,, globulin - - 0327 



(Fat ----- 0002 



/Consisting principally of potash 



.v. . TO I and soda, chlorides, some 



5 "j magnesia, a little lime, and 



I traces of phosphates. 



The proteins are thus seen to be serum albumin and globulin, 

 and their constant presence has been determined by a number 

 of observations ; the mineral matter is very high and consists 

 principally of soda and potash, especially the latter. It will 

 be observed that the mineral matter greatly exceeds the organic 

 matter ; in horses which have sweated freely the dried, matted 

 hair (which is due to albumin) is often seen covered with saline 

 material, looking like fine sand. There appears to be some 

 complemental action between the skin and the kidneys in the 

 elimination of soda and potash ; during rest the kidneys eliminate 

 these salts, while during work they are assisted by the skin. 

 Urea is also probably present in sweat (see p. 311). It is difficult 

 to see why horses should excrete albumin by the skin ; the loss 

 thus produced accounts for the great reduction of vitality and 

 strength in animals which sweat freely at work, and for which 

 clipping is the only preventive. 



Nervous Mechanism of Sweating. — A skin may sweat under 

 quite opposite conditions — viz., both with a hot flushed skin 

 and a bloodless cold skin ; in other words, an animal may sweat 

 when it is hot or when it is cold. The former is a physiological 

 condition and regulates, as we shall see, the body temperature ; 

 the latter is abnormal, but it occurs and disproves at once any 

 notion of sweating necessarily depending upon a congested 

 condition of the vessels of the skin. Experiments show that 

 most of the features of sweating can be accounted for through 

 the agency of the nervous system. Though we are ignorant of 

 the manner in which the nerves terminate in the sweat glands, 

 still, it is certain that there are special branches of nerves, whose 



* ' The Sweat of the Horse,' Journal 0/ Physiology, vol. xi., 1890. 



