But Baron fails to specify what were the projected experiments, or the difficulties which hindered their performance. It is a common nuisance in “sympathetic” biographies to have unlimited drafts made upon one’s credulity. The evidence of example would go to prove that Jenner placed his trust in swinepox rather than cowpox, at least as late as 1789.
In April, 1795, a general inoculation took place at Berkeley on Dimsdale’s plan; that is to say, all in the district who had not had smallpox were inoculated with the disease, so that they might sicken together and do no mischief. Among the Berkeleyans was one Joseph Merret, who, 1770, had attended horses with greasy heels and at the same time milked cows, and from the cows had contracted cowpox. Jenner inoculated him repeatedly with smallpox on this occasion, but with no effect; whence he concluded that the attack of cowpox in 1770 had maintained Merret secure from smallpox for five-and-twenty years.[93]
Jenner’s aim was now directed to demonstrate that the common faith in cowpox as a defence against smallpox was well-founded; and to do so it was necessary to clear away two objections--
FIRST, That some who had caught cowpox had subsequently suffered smallpox.
Various eruptions occur on the teats of cows, which are confounded with cowpox, and infect the milkers; and these, I admit, do not protect from smallpox.
In a letter to Edward Gardner in 1798 he remarked--
The _true_ has many imitations by the _false_ on the cow’s udder and nipples; and all is called _cowpox_ whether on the cow or communicated to the human.[94]
SECOND, That some who had contracted true cowpox had nevertheless fallen victims to smallpox.
Admitted: but then the milker had not received infection from the cow at the proper time, but at a stage of the eruption too early or too late.
If the reader will set these points clearly before him, he will have the measure of Jenner’s claim. It was a claim to define the truth there was in a popular belief--not to make an independent discovery.
Jenner at this juncture had staked his hope on the identification of horsegrease with cowpox. Yet even in this identification he does not seem to have been original.
It was a persuasion among the farmers that pox on the cows was derived from grease on the horse; and that infection with horsegrease was just as good against smallpox as infection with its derivative cowpox. The fact, however, of this derivation of cowpox from horsegrease was contested, but Jenner was positive. Writing in 1794 he said--