The hypothesis was, that smallpox inoculated on the cow lost somewhat of its virulence; but if so, why should not such cowpox inoculated on man resume its virulence? We are apt to forget that the nature of things is not controlled by our wishes, and that our interest in the conversion of smallpox into cowpox, and its maintenance as cowpox, is no warrant for fulfilment. I may also remark that though smallpox cowpox has entered so largely into currency, there is no evidence to what extent it has displaced the preceding issues of horsegrease cowpox, cowpox and horsepox. So far as we know, they are all existent in the common blood, indistinguishable, the stronger surviving, the weaker dying out: nobody knows, nor can know. CONDEMNATION OF SMALLPOX COWPOX. That smallpox cowpox is in any sense cowpox is, however, widely disputed, much confidence being placed in the researches of the Lyons Commission in 1855, presided over by M. Chaveau. This Commission, says Dr. Charles Cameron, “proved incontestably that smallpox can no more be converted into cowpox by passing it through a cow than by stunting an oak it can be converted into a gooseberry bush.” Cowpox, it is held, is a disease of the cow, with no relation to smallpox. The vesicles of each may be apparently identical, as are the vesicles excited by the application of tartar emetic; but that is no proof of essential identity. According to Dr. George Wyld, “Smallpox inoculation of the heifer produces not vaccinia, but a modified smallpox, capable of spreading smallpox among human beings by infection;” and Dr. Cameron boldly attributes the recent increase of smallpox to the use of smallpox cowpox for vaccination. Nor is Dr. Cameron singular in this opinion. Some time ago, the Galway Guardians ran short of virus for vaccination, when it was proposed to inoculate a calf with smallpox. As soon as the Local Government Board in Dublin became aware of the project, it was forbidden. Why? Here is the deliverance of the Secretary--“Because smallpox virus taken from the calf would communicate that disease to the human subject, and be thereby a fertile source of propagating the disease; and would, moreover, render the operator liable to prosecution under the Act prohibiting inoculation with smallpox.” Thus the virus current in England, and credited with miraculous virtue by Simon, is denounced as dangerous and its use unlawful in Ireland! COWPOX REVIVED. The constant disasters of vaccination, the certain and suspected communication of human diseases with the virus propagated from arm to arm, have induced a wide resort to cowpox under the designation of “animal vaccination,” in contempt of the fact that disease in cattle is as rife as among men, and inoculable. Still the dread of the invaccination of syphilis is so intense, and so justifiable, that other risks are encountered if that may be avoided.