Infectious Diseases of Animals. 241 



the symptoms wliicli are exhibited by the animal, and means are taken for its 

 cure. Most forms of skin disease in the horse, when they are considerably 

 advanced, are spoken of under the common term " mange ;" and, usually, 

 no pains are taken to discover the cause of the disease, but remedies are 

 immediately applied for its removal ; and generally it happens that the 

 measures in common use for the treatment of skin disease in the horse, are 

 sufficiently active to destroy the parasites if they are present. 



In the ox the mange acarus occupies certain isolated positions in different 

 parts of the body, and unlike the acarus of sheep-scab, exhibits no desire to 

 wander over the skin. Consequently mange in cattle is comparatively unim- 

 portant and very rarely spreads among the herd. 



Sheep-scab, however, when it appears in a flock, owing to the transfer of 

 the acari from a diseased animal, spreads very quickly. The disease is some- 

 times not detected by the shepherd until it has made some progress, for, 

 although the infected animals may show symptoms of the irritation, which 

 they experience in a fortnight after the acari have taken up their residence 

 on their skins, it is probable that no notice will be taken of the circumstance 

 until a number of animals of the flock are seen to rub themselves against 

 trees and posts, and occasionally nibble at the parts of their bodies whicli 

 they can reach with their mouths. 



It appears from exi^eriment, that in 10 days after the transference of the 

 acari to the skin of the healthy sheep, signs of irritation present themselves. 

 At the end of the fortnight there will be discovered moist spots in different 

 parts of the skin, chiefly on the back and breast. Before the expiration of 

 three weeks distinct scabs will be apparent, and by the end of a month the 

 affection will have so far advanced that there will be no difficulty in discover- 

 ing its true nature. 



The acari of sheep scab do not burrow in the manner of the itch insect of 

 man, but they cling to the wool and wound the surface of the skin with their 

 pointed mouths, thus causing irritation, which as it increases day by day in 

 consequence of the development of new broods of parasites, at last affects the 

 animal's constitution. The wool falls off, the animal loses condition, and at 

 last becomes exceedingly emaciated, and if the disease is allowed to run 

 its course unchecked, the sebaceous follicles become filled with secretion 

 and protrude from the surface of the body in small lumps, which have been 

 mistaken for the papulae of sheep-pox, with which disease scab is not un- 

 commonly confounded by ill-informed persons. 



No difference of opinion should ever exist as to the presence or absence of 

 sheep-scab, as, in the event of the disease existing, a little care will suffice for 

 the detection of the parasite which causes it. It is only necessary to take a 

 small quantity of loose scab and wool, place them on a sheet of white paper, 

 and carefully examine them by means of a pocket lens. The presence of the 

 acarus will be indicated by the movement which takes place among minute 

 portions of scab, and if these parts are carefully observed, the insect will be 

 «een to creep from its position, and may then be readily removed on the 

 point of a needle. 



If the sheep have been dressed for the cure of the disease previously to the 

 examination, and in consequence no live acari can be detected by the unaided 

 ej'e or with a pocket lens, it will be necessary to make a microscopic exami- 

 nation of the wool and portions of scab. 



This minute examination is absolutely required of a professional man before 

 he arrives at a conclusion, as, imder certain circumstances, the skin of the 

 sheep becomes covered with yellow exudations somewhat resembling the 

 product of the disease, and although there are very distinctive symptoms 

 which indicate sheep-scab irrespective of the discovery of the acari, this 

 positive evidence can always be obtained, and should always be sought for, 

 VOL. X. — S. S. R 



