VARICELLA. 743 



man or animal will, when mixed with vaccine 

 virus, prevent its action. 



Horsepox is identical with cowpox. Sheeppox 

 (clavelee) is an independent disease. The virus of cow- 

 pox produces a local lesion in the sheep, but does not 

 cause immunity to sheeppox. The virus of sheeppox, on 

 the other hand, has no effect on horses and cattle 

 (Nocard and Leclainche). The virus of sheeppox is 

 filterable (Borrel). 



viii. CHICKENPOX (VARICELLA). 



Although the skin manifestations of varicella 

 often resemble those of smallpox to such an 

 extent that differentiation is difficult, the two 

 diseases are distinct. Nothing indicates this more 

 clearly than the fact that one who has recovered 

 from varicella is susceptible to vaccination, and it 

 is known further that an attack of chickenpox 

 does not protect against smallpox. 



The etiology is unknown, and no organism 

 which has been described can be considered the 

 probable cause. 



Varicella occurs epidemically and sporadically. 

 The virus probably exists in the lesions of the 

 skin and in the scales, and the latter may be the 

 chief source of contagion. There is no definite 

 knowledge concerning the resistance of the virus, 

 nor its distribution; the conclusion is justified, 

 however, that it exists in the circulation at least 

 in an early stage of the disease. The infection 

 atrium likewise is a matter of conjecture, but 

 probably is to be found in the lungs or upper 

 respiratory tract. 



The patients should be isolated and school chil- 

 dren should not be allowed to return to school 



