SCABIES. 783 



varying extents of the body-surface ; in the third these are 

 confined, or nearly so, to the Hmbs. 



The first of the forms of body-mange is beheved to be 

 produced by the burrowing beneath the epidermis of the acari 

 known as the sarco'ptes ; the second, and in this country 

 probably the most common variety, depending on the residence 

 upon the skin, of those known as the i-)soroiJtes or dermato- 

 dectes ; while the particular mange of the limbs seems to owe 

 its origin to the collection in groups of a third variety of the 

 same family, the cliorioptes or symhiotes. 



c. Causation. — Although it is undoubted that the essential 

 and immediate factor in the production of mange in any form 

 is the presence of the mange mite, we may not shut our eyes to 

 the teachings of experience, in so far as these tell us that all 

 debilitating and exhausting influences, as exposure, fatigue, 

 want of sufficient food and fitting stabling, render horses more 

 susceptible to the attack and rapid development of the induc- 

 ing parasite, and of course materially influence the progress 

 and termination of the disease. The influences of these 

 agencies have been observed and their extent determined by 

 all observers, particularly by those associated with large 

 collections of animals in civil as well as military life. In the 

 latter condition this disease, along with glanders, has ever been 

 the scourge of armies in the field. 



No doubt animals of certain temperaments and constitutions 

 Avould appear more liable to be acted upon by the immediately 

 inducmg cause than others; while of all these varieties of 

 scabies, probably that which appears upon the limbs is most 

 disposed to exhibit a tendency to develop in connection Avith 

 individual peculiarities and dispositions. It exhibits, in addition, 

 also a distinct preference for cold over Avarm weather ; there is 

 here apparently existing a close relationship between the acari 

 of this variety, and the condition of the skin and its covering 

 at such seasons, peculiarly favourable for its life and pro- 

 pagation. 



Symptoms. — All the varieties of equine scabies are charac- 

 terized by the appearance of a class of symptoms having much 

 which is common. The truly diagnostic, however, is the 

 detection and recognition of the separate and individual acari. 

 In this country the form of scabies resulting from the presence 



