170 Veterinary Medicine. 



Vitality. The vitality exceeds that of the sarcoptes. Apart 

 from the host it survived lo to 14 days in a dry, genial atmos- 

 phere, and 20 to 30 days in moist stable air. Though apparently 

 dead it will often revive after six or eight weeks when subjected 

 to moist warmth. It does not bite, however, nor cause psoric 

 trouble. The ovigerous females survive the longest, and after 

 them the males. 



Transmission between different genera. Though no dif- 

 ference in structure can be detected in the psoroptes of the differ- 

 ent genera of hosts, yet when transferred from one genus to 

 another they rarely live long, but any eruption recovers spontan- 

 eously. According to Mathieu, Cagny and Cadeac an exception 

 must be made in the case of psoroptes auricularum of rabbits 

 which in their hands caused persistent acariasis in the horse. 

 Others have failed to transmit from the rabbit to the horse. 



Symptoms. There is the same intolerable itching which at- 

 tends on sarcoptic scabies, in many cases aggravated partly be- 

 cause of the rapid encrease of the parasites and centrifugal 

 extension of the infested area, and partly because of the secretion 

 of a more irritating venom. This last was shown by Gerlach, 

 who took on a needle the liquid exuded around the sarcoptes and 

 psoroptes respectively and punctured his own skin, when the 

 irritation which followed was materially greater in the case of the 

 psoroptes. While psoroptic scabies may be planted on any part 

 of the body, except perhaps the digits, and extends as a rule in 

 all directions and rapidly from the primary focus, yet a distinct 

 preference is shown for the parts covered by the strongest and 

 thickest hair (crest, rump, poll, back) where the most perfect 

 protection can be secured. There is less opportunity for its 

 spread on comb or brush from these parts, hence at the outset 

 there is less disposition than with sarcoptic mange to the forma- 

 tion of many new centres at distant points. After an existence of 

 a month or more the psoroptes may still be mainly confined to the 

 crest or rump. In extending it invades by preference the inter- 

 maxillary space, the breast, axilla, groin, and inner sides of the 

 thighs. Transference of the acarus in grooming may, however, 

 start it at any point. At first the bites and resulting sores or vesi- 

 cles are mainly isolated, but as the psoroptes encrease and crowd 

 each other the sores become confluent, and the exudate, infiltra- 



