438 THE DISEASES AND DISOKDBRS OF THE OX. 



Psoroptes ovis, which multiplies at a very rapid rate, and gives 

 rise to all the mischief by burrowing in the skin. We append 

 here a picture (after Gerlach) of the creature called by Gerlach 

 the Dermatodectes ovis, a very similar, if not the same, 

 creature. 



Sheep-scab is not uncommonly met with. It is very well known 

 to, and very justly dreaded by, all who have to do with sheep. 

 The Psoroptes ovis, though it closely resembles that of the horse 

 and that of the ox, is not capable of infesting these animals or 

 the goat. Moreover, when it gains access to the skin of a man, 

 it only produces a minute red spot, which does not even develop 

 into a papule. The rate of multiplication of the creatures is 

 very rapid. A single impregnated female Psoroptes will, in the 

 space of thirty-one days, give rise to the formation of a patch of 

 scabies nearly two inches in circumference. Some countries are 

 never free from sheep-scab, and from them the disease may 

 always be communicated to other places. Sheep fairs are 

 largely instrumental in the propagation of the disease, as also 

 are railway-trucks and cattle-boats, if they are not thoroughly 

 disinfected. 



Sheep-scab is very similar to, and, in fact, representative of, 

 the malady known as mange in the horse, ox, dog, and other 

 animals, and the disease commonly designated the itch among 

 mankind — a malady fortunately rather rare. In the case of the 

 sheep, scabies is of exceptional importance, owing to the fact 

 that the animal is provided with a thick coating of wool. The 

 little creatures which cause the disease are so well sheltered by 

 the bulky fleece that it is a matter of difficulty to poison them, 

 much more so, of course, than it is to effect the same object in 

 the case of animals which have but little natural covering on the 

 skin. Moreover, we must bear in mind that the skin of the 

 sheep is endowed with the very important special property of 

 producing the wool, and consequently that any cause which 

 markedly interferes with the functions of the skin must neces- 

 sarily be liable not only to give great distress to the animal, but 

 also to throw the working of the system at large sadly out of 

 gear. Again, the sheep, afflicted beyond all measure by the 

 itching, rubs and tears its skin with great violence, thus pro« 

 ducing much mischief. 



If the malady has once succeeded in establishing itself in any 



