348 Veterinary Medicine. 



South Africa, etc.) in the absence of imported infection remain 

 clear to the present day. 



The infection is n^ore intense and diffusible than that of cowpox 

 and horsepox following in this the smallpox of man. Absolute 

 contact is not necessary, in either case the infection is carried in 

 the air either on dust or otherwise, and above all in a confined 

 building, a crowded sheep fold or a du.sty highway. 



In all forms of variola the virulence is concentrated in the 

 lymph of the vesicle, and in horsepox and cowpox it is largely 

 confined to this, whilst in sheeppox in severe cases it must also 

 at times infect the blood, as lambs are occasionally born with 

 sheeppox. On this basis the infection of the secretions generally 

 has been advocated, but it is to be supposed that in moderate 

 cases these are contaminated after secretion. Nocard and Roux 

 produced immunity by the transfusion of blood from the sick to 

 the healthy, but in no case a variolous eruption. Even the sero- 

 sity from the swollen lymph glands failed to convey the disease. 



In view of the diffusible nature of the germ, however, we must 

 recognize that all secretions may be quickly contaminated as soon 

 as they are exposed, and therefore no product of a sick or sus- 

 pected sheep can be held to be safe, and all should be treated as 

 presumably infected. The most dangerous products and those 

 most liable to convey the disease are wool, hides, litter, build- 

 ings, yards, covers, parks, railway cars, boats, manure, urine and 

 milk. 



I<iving creatures like men, dogs, cats, birds, vermin, flies and 

 other predacious insects are occasional bearers of infection. 



Receptivity must be considered in every case. In countries and 

 districts habitually immune from sheeppox, all breeds appear to 

 be equally susceptible, the only refractory specimens being sheep 

 that have survived a first attack, and lambs born of ewes that had 

 the disease (naturally or inoculated) during the later stages of 

 gestation. New born lambs, on an exclusively milk diet, are 

 alleged to be somewhat refractory. In a country where sheeppox 

 has prevailed long and extensively, as in Algiers and Brittany, 

 certain breeds of sheep seem to have attained to a large measure 

 of immunity (Nocard). This is doubtless largely due to the sur- 

 vival of the more insusceptible strains of blood, as Algerian sheep 

 carried into France lead to most virulent outbreaks among the 

 native animals (Galtier). 



