298 INFECTIVE DISEASES. 



Sheep-pox and cow-pox are quite distinct diseases. Sheep-pox 

 is highly infectious, whereas cow-pox is only conveyed by direct 

 inoculation, and is never infectious, and further, cow-pox inoculated 

 in sheep does not produce sheep-pox. 



Bacteria in Sheep-pox. — Ilallier and Zurn, Klein, and others, 

 have found micrococci and bacteria in the lymph of the vesicles of 

 sheep-pox, but they are only accidental epiphytes. The nature of 

 the contagium is unknown. 



Protective Inoculation. — Extensive experiments were carried 

 out in England to test the protective power of vaccination against 

 sheep-pox. According to Marson and Simmonds, it was very difficult 

 to get cow-pox to take on sheep, and when an effect was produced, 

 the resulting affection, even when developed to its fullest extent, was 

 very unlike the same disease in the hviman subject. In the sheep 

 it seldom produced anything more than a small papule, which occa- 

 sionally resulted in the formation of a minute vesicle, or more 

 commonly, a pustule, which was sometimes, although very rarely, 

 surrounded by a slight areola. Generally, however, neither vesica- 

 tion nor pustulation followed, but a small scab was produced, which 

 soon fell from the site of the puncture, leaving no trace behind. The 

 disease passed quickly and irregularly through its several stages, 

 and terminated by the eighth or ninth day, and not unfrequently 

 even before that time. Lymph was but rarely obtainable, and then 

 only in the smallest quantity, and this on the fifth or sixth day suc- 

 ceeding the vaccination. The effects were only local, and the animal's 

 health was not impaired. 



Sheep were found to be just as susceptible of the cow-pox virus 

 on subsequent repetition of the inoculation as they were in the 

 first instance, and hence the conclusion that cow-pox was utterly 

 worthless as a protective against sheep-pox. According to Depaul, 

 however, cow-pox takes characteristically on sheep, and sheep-pox 

 lymph inoculated on cows produces a result indistinguishable from 

 the appearances obtained with the inoculation of cow-pox lymiph. 

 It is impossible to say whether these conflicting results depended 

 upon the employment in the experiments of different breeds of sheep 

 or different stocks of vaccine lymph. 



The objection to clavelisation or ovination is that the disease 

 may be introduced in localities where it was previously unknown. 

 By ovination, as in the analogous case of variolation, fresh centres 

 of infection are created, whereas every precaution should be taken 

 to prevent the introduction of the disease. 



Stamping-out System. — Sheep-pox has been imported into this 



