Woodville also argued, that “Cowpox, as casually produced by milking infected cows, differs considerably from that which is the effect of inoculation”; which Jenner attested in saying—
Four or five servants were inoculated at a farm contiguous to Berkeley last summer with matter just taken from an infected Cow. A little inflammation appeared on all their arms, but died away without producing a pustule; yet all these servants caught the disease within a month afterwards from milking the infected Cows, and some of them had it severely.[109]
Others maintained that the cowpox which saved milkmaids from smallpox was a much severer affection than that induced by Jenner’s lancet, and that it was folly to assume their equivalence. There was force in the argument; for every one then knew how much the issue of smallpox inoculation depended on the mode of its performance. The infection when communicated through the skin was usually much less severe than when communicated by incision; and Jenner related how a country inoculator, who liked to “cut deep enough to see a bit of fat,” was the death of his patients on every side. The human body is of infinite delicacy and complexity, and we are sure to find ourselves at fault when we deal with its mysteries according to our crude and inanimate logic. It is by experiment and not by syllogism that physiological truth is verified.
Whatever might be the perils, immediate or remote, of inoculation with cowpox, it was not attended with smallpox eruption; and at last it became manifest to Woodville himself, that the virus he had used, and the virus he had distributed, which had produced such eruption, was the virus of smallpox.
After much controversy and many experiments these conclusions were arrived at—
1. That when a person was inoculated with smallpox and cowpox about the same time, both inoculations proved effective. There was a pustular eruption on the skin from the smallpox, and the cowpox vesicle reached maturity in the usual number of days.
2. These effects took place, without much variation, in all cases where the interval between the two inoculations did not exceed a week; but—
3. When the smallpox matter was inserted on the ninth day after the inoculation with cowpox, its action seemed to be wholly precluded.[110]
That is to say, for a time—until the influence of the vaccine fever had worn off. Some fancied that smallpox when inoculated with cowpox generated a hybrid pox that was more efficacious than either. There was occasionally some interaction of the diseases, as of a subdued activity in each, but generally they proceeded together unaffected, the cowpox maintaining its characteristics in the midst of a crop of smallpox.
One point of great significance in Woodville’s experience was overlooked. He inoculated with cowpox in the Smallpox Hospital, and some of his patients there contracted smallpox, who certainly were not inoculated with smallpox, either accidentally or by design. The lesson of this experience was unperceived, and though it has been repeated again and again, is rarely acknowledged. Vaccination in presence of smallpox, or in an epidemic of smallpox, is often a means of inducing the disease it is intended to prevent. It lights the fire; and when the fire is lighted, it is said, “Ah! it must have been a-light before.” When we have a mind for an excuse, our sophistry is usually equal to the requisition.