VARIOLATION OF SIIKKP. 147 



failed to communicate tliis disease to sheep. Tlie 

 incisions into which the fluid was inserted put on an 

 ordinary appearance, and gave no indications of that 

 specific inflammation which marks a successful inocu- 

 lation. Whether the virus would prove uniformly inert 

 in an extensive series of inoculations, we are not pre- 

 pared to say ; probahly it would not ; for we have no 

 reason to beheve that the sheep is less susceptible of its 

 action than the cow. There is, however, always a 

 difficulty in transmitting an exanthematous affection, 

 apparently of the like kind, from an animal to another 

 of a different species, although it can be propagated 

 readily enough among animals of the same class ; while 

 from the numerous failures which occur, we miiiht 

 now and then be justified in concluding that some 

 creatures are entirely insusceptible to a virus which 

 easily acts on others. Modifications of the malady are, 

 however, more generally obtained, these being chiefly 

 referrible to the peculiarity of organism. 



The small-pox of the human subject, and the cow- 

 pox of the ox tribe, are believed by many eminent pa- 

 thologists to be so closely alhed, that a conveyance of 

 the affection from the former to the latter is said to 

 engender the true vaccine. Mr. Erasmus Wilson re- 

 marks, that " the transmission of small-pox to cattle by 

 means of inoculation, and the consequent development 

 of cow-pox in those animals, is established on abun- 

 dant e\'idence, for the chief of which we are indebted 

 to the zealous perseverance of Mr. Ceely, of Aylesbury. 

 It is stated by Dr. MacMichael, in an essay read before 

 the College of Physicians, in 1828, that ' vaccine matter 

 having failed in Egypt, medical gentlemen were led to 

 institute certain experiments, by which it has been dis- 



