MANGE. 137 



ERUPTION.— The nature of the eruption is due to the 

 venomous bites of the insects and to friction in the efforts made 

 by the suflfering animal to obtain relief from the itching by 

 scratching or rubbing itself. 



ITCHING. — The itching appears to be caused by the irritating 

 saliva these insects deposit on the wounds they make in 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 these 

 insects, which, in the two commonest forms (psoroptic and sar- 

 coptic) 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. Experiment has shown that the saliva 

 of the psoroptes is more irritating than that of the sarcoptes ; 

 consequently, itching from psoroptic punctures is more intense 

 than that caused by the sarcoptes. 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 

 increase in number, than on animals whose coats are carefully 

 attended to. Young horses 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. It 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. Symbiotic mange is but little catching. 



COMPARATIVE GRAVITY.— Psoroptic mange is a less serious 

 disease than the sarcoptic kind ; by reason of the more stationary 

 habits of the parasite, it spreads slower, and is less contagious ; 

 and can be more readily cured, owing to the fact that the insects 

 do not burrow into the skin. 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 very deeply wrinkled crests. Symbiotic mange is in everj 

 way a milder disease than the other two. 



