MANCiE. 137 



the skin, with the object of producing and obtaining serum (the 

 fluid contained in a blister) for their food. The intensity of the 

 itching is proportionate to the number and state of activity of tliese 

 insects, which, in the two commonest forms (psoroptic and sarcoptic) 

 of mange, are more or less dormant under the influence of cold, 

 and busy under that of heat. Hence this itchiness is particularly 

 observable at night when the horse is well clothed and comfortably 

 stabled. Gerlach has shown by experiment that the saliva of the 

 psoroptes is more irritating than that of the sarcoptes, and con- 

 sequently that the itching produced by the punctures of the former 

 is more intense than that caused by those of the latter. The 

 itching of symbiotic mange is much less severe than that of the 

 other two. 



PREDISPOSITION. — There seems to be no such thing as pre- 

 disposition to mange beyond the fact that on ungroomed horses, 

 the parasites are given greater facilities to invade the skin and to 

 increase in number, than on animals whose coats are carefully at- 

 tended to ; and that young horses, according to Raillet, are much 

 more liable to contract symbiotic mange than older ones. 



CONTAGIOUSNESS. — Sarcoptic mange, owing to the roving 

 habits of its parasites, is extremely contagious, especially when it 

 has assumed a chronic form ; and may be communicated even by 

 brief contact, and by the medium of clothing, bedding, stable gear, 

 etc. The psoroptic form, though less contagious than the sarcoptic 

 kind, can be readily transmitted from one horse to another. Sym- 

 biotic mange is but little catching. 



COMPARATIVE GRAVITY.— Psoroptic mange is a less serious 

 disease than the sarcoptic kind ; for, by reason of the more sta- 

 tionary habits of the parasite, it spreads more slowly, and is less 

 contagious ; and, owing to the fact that the insects do not burrow 

 into the skin, it can be more readily cured. When sarcoptic mange 

 has spread all over the horse's body, it may be regarded as nearly 

 if not quite incurable. Even when recovery is possible, it will 

 require several months of persistent treatment. Trasbot points 

 out that psoroptic mange is sometimes incurable in entire horses 

 which have their crests very deeply wrinkled. Symbiotic mange 

 is- in every way a milder disease than the other two. 



VITALITY OF THE PARASITES.— According to Gerlach, pso- 

 roptes may live under favourable circumstances, when removed from 

 their host, as long as two months ; sarcoptes, about half that time. 



INCUBATION. — The period required for the eggs of the mange 

 insect to become hatched, varies according to temperature, within, 



