VARYING SUSCEPIIBILITY. 69 



racter of the disease is fully established, and this goes 

 very far to prove its infectious nature, althouf^h many 

 causes besides may be in operation to produce its 

 extension, in that peculiar form. 



It is generally admitted that, whenever variola is 

 introduced among sheep, neither the locahty they in- 

 habit nor the system of their management or feeding, 

 nor age, sex, or breed, gives security from an attack, 

 or prevents the malady from spreading. But it has 

 been noticed that some of the flock fall victims to 

 the effects of the disorder much earlier than others, 

 arising from their greater susceptibility to receive the 

 poison. Young sheep seem to be the most prone 

 to take it. The true why and wherefore of this 

 phenomenon, or of other portions of the same flock 

 resisting the attack for a longer period, cannot be 

 satisfactorily explained. 



According to the French authors, the early cases 

 are mostly mild, and the subsequent ones severe, with 

 the exception of the very last, when the disease is again 

 less destructive. Our experience, however, does not 

 confirm these statements. 



Several well-marked instances of sheep remaining 

 unaffected for a considerable period have come to our 

 knowledge : trvo of these took place on the farm of 

 Mr. J. Weall, a month having passed after the animals 

 were first exposed to the contagion, by living with the 

 diseased, before their health was affected. In Mr. 

 Statham's letter (see page 58), a question is put to us 

 on this subject; and it appears, by the date of his 

 conmnmication, that tzoo months elapsed before the 

 Merino to which he alludes shewed any symptoms of 

 the malady, although it had remained with his in- 



