DISEASES OF THE SKIN. 327 



of sebaceous glands, and thus shed water. The hairs, through their 

 elasticity, furnish mechanical protection, and through the thickness of 

 the coat, to a certain degree, 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 regu- 

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

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

 ing of the body. Sweating, in addition to regulating heat, is also an 

 active agent in removing eftete material from the blood; therefore this 

 secretion can not be checked without danger to the animal. If the skin 

 be cove- red 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 modi- 

 fied 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 is intended to lubricate the skin and hairs. 

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

 ized 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 only serve to confuse the reader. 



We will 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. 



PKURITIS ITCIIIXG. 



'We will 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 symp- 

 toms accompanying the majority of the diseases which we will consider 

 in this work. It may truly be considered ;v neurosis, or increased sen- 

 sibility of the skin hypi'i'a'xlhvxin, dependent upon nervous excitability. 

 It is, then, a functional affection, nerve disturbance, unaccompanied by 

 primary structural changes in the skin. Nothing is seen except the 

 secondary lesions, produced mechanically by scratching or rubbing. 



There are various fonM of itching, the result of specific skin diseases, 

 where* the pruritis is ft secondary symptom. In anch cases it should 

 not bo regarded an an affection. 



('nw*. Many cause* may induce the condition which we recogni/e 

 here as pruriti*. The mo*! common one is gastro-intesttnal irritation. 

 Thin condition is often witnessed in cattle suffering from impaction or 

 inflammation of the third stomach, and has been called mad itch,' 1 from 

 the fact that the affected animal manifested a mad fury in rubbing cer- 

 tain portions of the lody, even to lacerating the skin on the sides of tin 1 

 body and legs with the teeth. In attacks of dysentery I hnve nten 



