VIl] THE FUNCTIONS OF THE SKIN 89 



capillaries not unlike the glomeruli of the kidnej's. The secretion 

 (sweat or perspiration) contains protein, fat, salts and A\ater and 

 is alkaline in reaction. 



Sebaceous glands. Sebum is the greasy material secreted by 

 the sebaceous glands. These lie alongside of the hairs and 

 communicate by short ducts with the hair follicles. The secretion 

 lubricates the hairs, and in horses gives gloss to the groomed coat. 

 It also helps to keep off wet. 



Dandruff, which is the material removed in grooming a horse, 

 consists of epithelial scales, fat, sebum, etc. 



The functions of the skin are five in number : 



(1) Protective. 



(2) Sensor}'. 



(3) Respiratory. 



(4) Absorptive. 



(5) Heat-regulating. 



(1) The skin supplies a strong elastic coating for the body. 

 It is thickest at places where injury is most frequent. 



(2) The skin is an organ of touch being highly endowed with 

 sensory nerve endings, especially in certain parts (e.g. the region 

 of the external generative organs). 



(3) The respiratory function is practically negligible in 

 mammals and birds, but in some lower Vertebrata it is well 

 developed. Thus frogs can live by breathing through their skin 

 after the complete removal of the lungs. 



(4) The skin's capacity for absorption is very slow in 

 mammals though it definitely exists. Colin kept the lumbar 

 region of a horse wet with a solution of potassium ferrocj-anide 

 and found traces of the salt in the urine after 4i hours. The 

 ill -effects of varnish on the skin are not owing to absorption, but 

 are due to the fact that the varnish causes the capillaries to dilate 

 and so produces an undue loss of heat. 



(5) The heat-regulating mechanism possessed by the skin of 

 all 'warm-blooded' animals is of very great importance. It is 

 well known that in mammals and birds the temperature of the 

 body is generally warmer than that of the surrounding air. 

 Moreover, under normal conditions it keeps approximatel}'^ 

 constant, notwithstanding the varying temperatures to which 

 the animal is exposed. This fact is implied in the term homoio- 

 thermal, which is applied to such animals, (^n the other hand 



