Happening, on the 14th of June, to be with Mr. Lucas, apothecary, on professional business at Mr. Willan’s farm, adjoining the New Road, Marylebone, where from 800 to 1000 milch cows are kept, I availed myself of the opportunity to make inquiry concerning the Cowpox. I was told it was a pretty frequent disease among the cows of that farm, especially in winter, and that it was supposed to arise from sudden change from poor to rich food. It was also well known to the servants, some of whom had been affected with the malady from milking the diseased cows. On investigation, I found that three of the men-servants, namely, Thomas Edinburgh, Thomas Grimshaw, and John Clarke had been affected with the Cowpox, but not with the Smallpox. I induced them to be inoculated for the Smallpox, and, with the view of ascertaining the efficacy of the variolous infection employed, William Kent and Thomas East, neither of whom had either the Cowpox or the Smallpox, were also inoculated. (P. 14.) 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.