Thus Horsegrease sores so simulated those of Cowpox, or of Horsegrease Cowpox, as to be indistinguishable from them. At this time it was Jenner’s opinion that Horsegrease, _per se_, afforded no protection from Smallpox: it had to pass through the Cow to acquire its sovereign efficacy. The opinion is noteworthy in view of its absolute surrender at a later period, when the virus from the Horse’s heel came to be described by him as “the true and genuine life preserving fluid,” and was used by him for inoculation without any reference to the Cow. One of the aims of _Further Observations_ was “to enforce the precaution of subduing the inoculated pustule as soon as it had sufficiently produced its effect on the constitution.” True Cowpox, according to Jenner, was a serious affection. “The sores ate into the flesh.” (P. 77.) They were capable of producing violent effects. They were attended with erysipelas. “They closely resembled Smallpox of the confluent sort.” (P. 111.) To prolong such suffering he considered useless, for the virus conferred its protective influence on the constitution as soon as received-- The symptoms which (as in the accidental Cowpox) affect the patient with severity, are entirely secondary, excited by the irritating processes of inflammation and ulceration; and it appears to me this singular virus possesses an irritating quality of a peculiar kind; but as a single Cowpox pustule is all that is necessary to render the variolous virus ineffectual, and as we possess the means of allaying the irritation, should any arise, it becomes of little or no consequence. (P. 110.) The means for allaying the irritation were mercurial ointment, acetate of lead, caustic potash, or any suitable escharotic-- After the pustule has duly exerted its influence, I should prefer the destroying it quickly and effectually to any other mode. The term caustic to a tender ear (and I conceive none will feel more interested in this Inquiry than the anxious guardians of a nursery) may sound harsh and unpleasing, but every solicitude that may arise on this account will no longer exist when it is understood that the pustule in a state fit to be acted upon is then quite superficial, and that it does not occupy the space of a silver penny. (P. 104.) I would not, however, recommend any application to subdue the action of the pustule until convincing proofs had appeared of the patient having felt its effects for at least twelve hours. No harm indeed could ensue were a longer period to elapse before the application was made use of. In short, the pustule should be suffered to have as full an effect as it could, consistently with the state of the arm. (P. 109.)