Gaulard then declares, “that though reason dictates, and _experience actually demonstrates_, that this process (inoculation for Small Pox) does not infallibly afford protection against a subsequent attack of natural Small Pox, he was still disposed to believe that it may be possessed of some real advantages” (p. 59). “Dr. Cantwell, in 1755, published a dissertation upon inoculation, the avowed object of which was to _undeceive_ those who believed in the efficacy of that practice. In this Essay, a great number of cases of Small Pox, which had occurred both after natural and inoculated Small Pox, are mentioned” (p. 64). “He (Dr. Cantwell) seems to have been well acquainted with those varioloid eruptions which, previous to the introduction of inoculation, had received a variety of names, such as Swine Pox, Chicken Pox, &c. and which were considered not as specifically different from Small Pox, but as spurious and bastard species of that disease. These eruptions, in his opinion, were nothing else than mild varieties of the true Small Pox. His own words are” (p. 37), “after all, what are the Swine Pox, the Duck Pox, and the Chicken Pox, which are observed among the English and the Irish? What is the _petite verole volante_ which is seen in France? Many distinguished authors attest, that they have seen Small Pox occur twice in the same individual; and have not we reason to believe that, in these cases, the second attack was true Small Pox, of which the infection was slight, and in which the vital actions were too weak to carry it to a certain extent?” All this appears to me most strictly consistent with truth. But Dr. Cantwell was arguing against the use of inoculation. How then did he account for the fact that “the infection was slight,” and that “the vital actions were too weak to carry it to a certain extent,” if it did not arise from these individuals having already passed through the disease of Small Pox? “De Haen (a celebrated physician of Vienna,)” says Dr. Thomson (p. 68), “collected into a body the numerous cases of secondary Small Pox, which are to be found in the writings of physicians, who lived previous to, and in the infancy of, the practice of inoculation in Europe. Had the number of these cases, and the respectability of the individuals by whom they are related, been duly considered, they surely were more than sufficient to have satisfied the minds of the most incredulous, of the possibility, and even of the frequency of secondary Small Pox.” De Haen, however, was an opposer of inoculation, and the facts he adduced were not permitted to have the weight which they merited, in consequence of the arguments he deduced from them. I shall conclude my extracts from the fund of evidence collected in the work of Professor Thomson, with the following:—