Variola : Sheeppox. 395 



become firmer and less tender, and shows in the centre a paler 

 area where the exudation has resolved it into a vesicle. The 

 characteristic sheeppox vesicle is rounded or flattened on its 

 summit, being rarely pointed as in smallpox, or umbilicated as 

 in cowpox. It is usually surrounded by a pink zone, which is at 

 times infiltrated, firm and resistant. After about the sixth day, 

 the vesicle becomes yellowish from the formation of pus. The 

 pustules, with the surrounding tumefaction, encrease for about 

 three days, when if they have not become confluent nor infected, 

 they begin to dry up, acquiring a grayish crust on the surface 

 which gradually encreases to a thick scab, which in five or six 

 days more is detached leaving a pink, pitted spot covered by 

 forming epidermis. Sometimes no distinct scab forms, but the 

 crust dries, cracks up, and falls off in scales. 



All the vesicles do not appear at once, but some earlier and 

 some later, so that the successive stages of the eruption may be 

 often seen together on the same subject, and the case is thereby 

 materially prolonged. 



As in other forms of variola the hyperthermia usually subsides 

 with the appearance of the eruption, but as often re-appears in 

 some measure with pustulation (secondary fever of reaction), and 

 becomes more severe in proportion to the extent and confluence 

 of the eruption and the occurence of complex infection. 



The eruption may invade the conjunctiva, the cornea (induc- 

 ing blindness), the nasal mucosa (causing difficult breathing), 

 the niouth (salivation, difficult mastication), the pharynx (diffi- 

 cult deglutition), the stomach and intestines (diarrhoea), the 

 bronchia (cough), or the vulva. 



With the occurence of desiccation, in discrete cases, the fever 

 subsides, the swelling of the skin and head dissapears, the dis- 

 charges from the nose and eyes cease, and the animal is restored 

 to health. 



A secondary eruption will sometimes take place, but only 

 papules form, which disappear without reaching maturity. 



The duration of discrete sheep pox is usually about three 

 weeks, but it may reach four in cool weather. It is more rapid 

 and more prone to dangerous complications in hot weather. As 

 the members of a flock are usually attacked in succession, it may 

 take three months to pass through a flock. 



