HISTORY 521 



lation, in other cases there develops after the inoculation firm 

 nodules which without changing to vesicles heal without scab- 

 bing (Chauveau) or else the inoculation remains without 

 results. 



The experimental evidence seems to show that the infect- 

 ing element of human variola and that of cows (vaccina) offer 

 two different modifications of one and the same pox contagion. 

 Fischer as well as Eternod and Haggins tried also to prove 

 this by the fact that the pox lymph inoculates back again into 

 man after which, in many thousands of people inoculated in 

 this manner, only a local pox eruption developed. The above 

 named authors, as well as Roloff and Bollinger, draw the con- 

 clusion from this that variola in its transmission through the 

 bodies of cattle changes to vaccinia and that the latter there- 

 fore presents nothing but a weakened modification of the first. 

 That this change does not always take place easily and in the 

 above mentioned way is shown by the experiments of Chau- 

 veau, who after inoculating with the lymph taken from cows 

 inoculated with variola saw the pox repeatedly appear in men 

 as a severe general disease. 



The very close relationship between human variola and 

 vaccina is shown through the fact that the vaccine produces a 

 lasting immunity to the variola. Since the local illness in 

 man following vaccination is a mild form of human pox, vac- 

 cine must be considered as a weakened form of variola virus. 

 If one considers further that the transmission of the contagion 

 from person to person, as such inoculations were usual in the 

 past, in most cases produced only a local lesion, so that in 

 cattle the pox as a rule, perhaps almost always, appeared as a 

 result of the transmission of the virus from a person sick with 

 inoculation pox, the conclusion is well founded that the con- 

 tagion of cow pox really presents a weakened modification of 

 the human pox virus. 



Jenner was of the opinion that cow pox appeared 

 as a result of infection by horses sick with pox and therefore 

 concluded that it was' identical with cow pox. Later Lafosse 

 and afterwards Bouley agreed with this opinion. Under the 



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