The result conformed to expectation: Edinburgh, Grimshaw, and Clarke did not take Smallpox, even though inoculation was repeated, whilst Kent and East did. Pearson set forth his experiments much more philosophically than Jenner, but his bias was pronounced, and it blinded him to some obvious considerations; and it is marvellous how easily we may accumulate details for which we have a fancy. Summing up the testimonies he had collected, he held that--
The body of evidence is numerous and respectable, declaring that a person who has laboured under the Cowpox fever and local eruption, is not susceptible of the Smallpox. It does not appear that a single well authenticated contravening instance has fallen under observation. But I do not apprehend that accurate and able reasoners will consider the fact as completely established, though, I doubt not, they will allow that the testimonies now produced greatly confirm the probability, and that the cautious appropriation of it in practice is warrantable. (P. 64.)
In this summary we perceive the limit and imperfection of Pearson’s _Inquiry_. Smallpox _did_ follow Cowpox: it was well known that it did: and Dr. Ingenhousz ascertained the fact as soon as he looked for it. Moreover Pearson showed himself ignorant of Jenner’s position, who, recognising the fallacy of the rural superstition, was compelled to discriminate Cowpox as genuine and spurious--the genuine being the variety derived from Horsegrease.
Upon Jenner’s assertion that Cowpox was unaltered by transmission from arm to arm, Pearson remarked, “The fact remained to be proved.” That Cowpox produced a harmless ailment was not, he thought, to be hastily assumed. Dr. William Heberden had recently inoculated 800 poor persons at Hungerford without a mishap, and 1700 had passed through Dr. Woodville’s hands in the current year (1798) with only two deaths; yet how erroneous would be to argue that variolous inoculation was harmless from such special experience!
Such instances of success can only be attributed to a certain favourable epidemic state of the human constitution itself, existing at particular times, for the proportion of deaths from inoculation is usually much greater, owing, probably, to certain unfavourable epidemic states. (P. 67.)