322 DISEASES OE CATTLE. 



regulators of the temperature of the body. Hence, in warm weather, 

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

 overheating of the body. Sweating, in addition to regulating heat, is 

 also an active agent in removing effete material from the blood; there- 

 fore this secretion can not be checked without danger to the animal. 

 If the skin be covered with an impermeable coating of grease or tar, 

 death results from blood poisoning, due to the retention of materials 

 destined to be excreted by the skin. 



The total amount of secretion poured out by the skin is not only 

 modified by the condition of the atmosphere, but also by the char- 

 acter and quantity of the food, by the amount of exercise, and espe- 

 cially by the quantity of fluid taken. 



The sebaceous secretion is intended to lubricate the skin and hairs. 

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

 terized by a special 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 due to faulty secretion and abnormal growth; 

 then, diseases of parasitic origin; and, lastly, local injuries of the skin. 



PRURITIS (ITCHING). 



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

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

 symptoms accompanying 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 down, the skin is irritated and pru- 

 ritis 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. 



Another cause is found in affections of the liver and of the kidneys, 

 when an increase of effete material has to be thrown off by the skin. 

 Morbid materials circulating in the blood may produce a tickling or 

 smarting sensation of the skin in their passage from the blood to the 

 free surface of the skin. Certain irritating substances when eaten may 

 be excreted by the skin, and coming thus in direct contact with the 



