i8o Veterinary Medicine. 



that it virtually ruined the local sheep industry. Even to the 

 present time and in our eastern markets scabby sheep are fre- 

 quently presented, and the railroad rolling stock, feeding yards 

 and market pens become contaminated infesting all coming ship- 

 ments, and transmitting the disease in the home flocks of the 

 unwary flockmaster. 



The parasite (psoroptes scabi var. Ovis) presents such in- 

 significant differences in size and otherwise from the species in- 

 festing horse and ox respectively that it cannot well be dis- 

 tinguished by external appearance alone. It presents the general 

 characters of the psoroptes communis, but otherwise it must be 

 distinguished by its habitat on the .sheep the only animal on 

 which it has been found to make a permanent home. Trans- 

 ferred to the skin of man or of other animals it bites and causes 

 transient irritation but speedily dies. 



Vitality. Experiments of Hertwig, Gerlach and Delafond 

 show that apart from the living sheep, this psoroptes can live on 

 wool or fresh skin, or even on litter or woodwork for from ten to 

 twenty days. In genial weather it remains active, and in cold it 

 becomes torpid, but when .subjected to moist warmth it soon re- 

 sumes its active movements. It dies promptly if the litter, wool 

 or other objects, in which it hides, are subjected to a zero tem- 

 perature. 



Accessory Causes. In so destructive a parasitism, every- 

 thing that favors infection should be constantly kept in mind. 

 Poor, low conditioned and neglected sheep are especially recep- 

 tive of the disease, but this must not be held to mean that it is 

 safe to expose the finest, best kept and most thrifty animals. It 

 refers rather to rapidity of progress of the malady caught, and 

 the sinking of the individual sheep under its effects, than to any 

 chances of escape from infection. Crowding of sheep together, 

 as in pens for washing, shearing, shipping, etc., gives more 

 abundant opportunitj' for transference of the parasite and 

 renders it much more active. Shearing by expcsing the infested 

 .skin more thoroughly favors the lodgement of the acarus on the 

 skins of others directly or on rubbing posts, stones and other in- 

 termediate bearers. The neglect of clipping may act injuriously 

 as the tufts of wool which are shed, and left in pastures, yards 

 and on rubbing objects carry the parasite with them. Unfenced 



