George Gregory, M.D., Physician to the London Small-pox and Vaccination Hospital.

Dr. Jenner suggested the notion that cow-pox possesses powers adequate to the extirpation of small-pox from the face of the earth. page 8 The doctrine that cow-pox possesses an exterminating power assumes, first, that small-pox arises invariably from contagion; secondly, that the susceptibility of cow-pox is universal in mankind; and, thirdly, that the influence of vaccination is permanent through life. All these are questionable points, and therefore on physiological grounds the notion must be abandoned. Vaccination, then, we confidently affirm, can be maintained only by having small-pox constantly before our eyes; and nothing warrants us in the expectation of banishing the bane by even the liberal application of the antidote.—Elements of the Theory and Practice of Medicine. 5th Edition. London, 1839.