There are many, who from some peculiarity in the habit resist the common effects of variolous matter inserted into the skin, and who are in consequence haunted through life with the distressing idea of being insecure from subsequent infection. A ready mode of dissipating anxiety originating from such a cause must now appear obvious. And, as we have seen that the constitution may at any time be made to feel the febrile attack of Cow-pox, might it not, in many chronic diseases be introduced into the system, with the probability of affording relief, upon well-known physiological principles? Although I say the system may at any time be made to feel the febrile attack of Cow-pox, yet I have a single instance before me where the virus acted locally only, but it is not in the least probable that the same person would resist the action both of the Cow-pox virus and the variolous. Elizabeth Sarsenet lived as a dairy maid at Newpark farm, in this parish. All the cows and the servants employed in milking had the Cow-pox; but this woman, though she had several sores upon her fingers, felt no tumors in the axillae, nor any general indisposition. On being afterwards casually exposed to variolous infection, she had the Small-pox in a mild way.--Hannah Pick, another of the dairy maids who was a fellow-servant with Elizabeth Sarsenet when the distemper broke out at the farm was, at the same time infected; but this young woman had not only sores upon her hands, but felt herself also much indisposed for a day or two. After this, I made several attempts to give her the Small-pox by inoculation, but they all proved fruitless. From the former Case then we see that the animal economy is subject to the same laws in one disease as the other. The following Case which has very lately occurred renders it highly probable that not only the heels of the horse, but other parts of the body of that animal, are capable of generating the virus which produces the Cow-pox. An extensive inflammation of the erysipelatous kind, appeared without any apparent cause upon the upper part of the thigh of a sucking colt, the property of Mr. Millet, a farmer at Rockhampton, a village near Berkeley. The inflammation continued several weeks, and at length terminated in the formation of three or four small abscesses. The inflamed parts were fomented, and dressings were applied by some of the same persons who were employed in milking the cows. The number of cows milked was twenty-four, and the whole of them had the Cow-pox. The milkers, consisting of the farmer's wife, a man and a maid servant, were infected by the cows. The man servant had previously gone through the Small-pox, and felt but little of the Cow-pox. The servant maid had some years before been infected with the Cow-pox, and she also felt it now in a slight degree: But the farmer's wife who never had gone through either of these diseases, felt its effects very severely.