320 DISEASES OF CATTLE. 



water. Through their elasticity they furnish mechanical protection, 

 and through the thickness of the coat, to a certain degi'ee, resist the 

 attacks of insects. Finally, the hairs assist the sense of touch. 



The sweat glands are constantly discharging a watery secretion in 

 the form of insensible perspiration, and by their influence act as 

 regulators of the temperature of the body : hence, in warm weather, 

 the secretion of the skin is increased, which tends to prevent over- 

 heating. Sweating, in addition to regulating heat, is also an active 

 agent in removing effete material from the blood; therefore this 

 secretion can not be checked without danger. If the skin is covered 

 with an impermeable coating of grease or tar, death results from 

 blood poisoning, owing to the retention of materials destined to be 

 excreted by the skin. 



All secretion poured out by the skin is not only modified by the 

 condition of the atmosphere but also by the character and quantity 

 of the food, by the amount of exercise, and especially by the quantity 

 of fluid taken. 



The sebaceous secretion isintended to lubricate the skin and hairs. 

 It consists of soft, fatty material suspended in water, and is charac- 

 terized by an odor peculiar to the animal by which it is secreted. 



I will not attempt to classify the various diseases of the skin, for 

 in a work of this kind it would serve only to confuse the reader. 



We shall first consider a class of diseases which are of an inflamma- 

 tory type; next, those caused by faulty secretion and abnormal 

 growth; then, diseases of parasitic origin; lastly, local injuries of 

 the skin. 



PRURITIS (ITCHING). 



We shall consider pruritis first as a distinct subject. It is not a 

 disease, only a sensation, and therefore a symptom. It is one of the 

 symptoms accompanjdng the majority of the diseases which we will 

 consider in this chapter. It is, then, a functional affection produced 

 by slight irritation from without or by an internal cause acting 

 upon the sensory nerves of the skin. Nothing characteristic is seen 

 except the secondary lesions, produced mechanically by scratching or 

 rubbing. 



There are various forms of itching, the result of specific skin dis- 

 eases, where the pruritis is a secondary symptom. In such cases it 

 should not be regarded as an independent affection. 



Causes. — Many causes may induce the condition which we recog- 

 nize here as pruritis. The most common one is dirt on the skin, 

 resulting from insufficient care. If the ceiling of the stable is open, 

 so that dust and straw may fall, the skin is irritated and pruritis 

 results. It also occurs in some forms of indigestion. 



The parts of the body most exposed to this condition are the croup, 

 the back, the top of the neck, and the root of the tail. 



