652 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



consequence, a thicker coat in winter than in summer. This is not only 

 seen in the thicker fur in animals which inhabit a cold climate, as con- 

 trasted with the same species in warmer latitudes, but also in the periodic 

 growth and shedding of hair seen in the horse and ox in the change of 

 the seasons. The hairs also furnish protection against wet, from the fact 

 that they are always more or less oily, from the secretions of the sebaceous 

 glands, and thus shed water. The hairs, throiTgh their elasticity, furnish 

 mechanical protection, and through the thicknesS of the coat, to a certain 

 degree, resist the attacks of insects ; thus the external auditory meati, 

 the external nares, and the eyes are protected by hairs. Finally, the hairs 

 assist the sense of touch. 



1. The Sweat Secretion. — The sweat-glands, which are found only 

 in mammals, occur in their simplest form in the domestic animals in the 

 ox, where they are simply oval sacs, which in man and the horse and in 

 the feet of the dog and cat and snout of the hog become developed into 

 long, convoluted tubes, passing through the entire thickness of the skin. 



In the horse the sweat-glands are comparatively highly developed, 

 especially in the inguinal region, where they are also abundant in the 

 sheep. In the ox the sweat-glands, as already mentioned, are rudimentary, 

 and, as a consequence, this animal sweats but very little. Cats, rabbits, 

 and rats do not sweat at all, the carnivora generally sweating only in the 

 soles of their feet. 



The sweat is a transparent, colorless liquid with a characteristic 

 odor, varying as to its source from different parts of the skin, with a 

 salty taste. Its specific gravity is about 1004." Its reaction may be 

 said to be normally alkaline or neutral. The frequent acid reaction is to 

 be attributed to the development of fatty acids in the decomposition of 

 fatty matters formed by the sebaceous glands, and which are ordinarily 

 mixed with the perspiration. Its quantity is very variable, governed by 

 conditions to be referred to directly. It may be stated in a general way 

 that, as a rule, twice as much water is given off by the skin as by the 

 lungs, while, as a rule, in man eleven grains of solids are eliminated by 

 the skin in twenty-four hours, in contrast to seven grains removed by 

 the lungs. The sweat contains no structural elements with the exception 

 of epithelial scales, which may be accidentally removed from the 

 epidermis. 



The sweat in its composition contains about 1.8 per cent, of solids, 

 of which two-thirds are inorganic and mainlj' constituted by alkaline 

 chlorides. The nitrogenous constituents of the sweat consist almost 

 solely of urea, which bj- its decomposition may give rise to ammonia. 

 The non-nitrogenous constituents of the sweat are composed of volatile 

 fatty acids, such as formic, acetic, butyric, proprionic, and caproic, which 

 give to the sweat its characteristic odor. Cholesterin and neutral fats 



