The patholobical principle by which the present state of our knowledge directs us to explain this fact is, that, where the infection of the small-pox comes in contact with a vaccinated constitution, it meets with a diminished sus ceptibility, which, in most instances, obviates every ten dency to the actual production of small-pox, and almost always obviates the fatal tendencies which it otherwise brings along with it.
From numerous other_ facts which presented them selves, we had been led lately to conclude that it affords a sure protection against the occurrence of the secondary fever, the principal danger of small-pox. We have, in deed, recently heard of an exception to this conclusion ; a vaccinated person who has been known to die under se condary fever. This is not in conformity to any thing we have seen, and must be a phenomenon still more rare than the exceptions to which we have referred. As tenacious advocates for vaccination, we are obliged to declare it as our opinion, that those who agree with us in this feeling will do much less justice to this preventive, by pronounc ing all the alleged exceptions to its efficacy to be cases of chickenpox, than by allowing that small-pox may occur after it, and by insisting rather on the comparative safety, than the great infrequency, of the disease under such cir ccmstances.
It has sometimes been intimated that, " as the laws of nature are uniform, such exceptions are lirinia facie impro bable ; and that it is most rational to infer, when they ap parently occur, that either the cow-pox, or the subsequent small-pox, is different from the corresponding disease, in the form in which the one is a preventive of the other." This may be the case. The exceptions may proceed from some cause of a powerful and decided nature. That cause may be discoverable by human inquiry; or, it may lie so deep as to mock our researches But, let us re member that, in the present state of our knowledge. we have other facts which warrant us, from analogy, in allow ing that such modifications of the animal system may not be absolute and invincible, but may exist in different de grees. Here it will be useful to revert to some well known „Iireumstances connected with small pox. Even a person who has already had that disease, either from casual in fection or inoculation, though most frequently secured against it in future, is not always secure. Some are at
tacked even when the exposure is casual, and not remark ably intimate or long continued. Others are secured in a greater degree, so as never to take the disease unless in close and long contact witn a varioious patient. On such exposure, a disease which has been called local, and which certainly is partial, may be generated. A nurse who has passed the small-pox has found variolous pustules breaking out on her breast while she suckled a child under that disease. These pustules, though their number may be considerable, are generally confined to one part of the body. They are seldom attended with any fever : yet, in other instances, febrile symptoms have in a slight degree appeared. Such symptoms are then generally attributed to mere irritation, and their true variolous nature is deni ed. It appears most philosophical to consider all these va rieties as evidences that the correction of this suscepti bility is liable to gradations. Such gradations, we think, take place remarkably in the influence of cow-pox. But, obscure as their causes are, and unable as we yet are to tell in what degree they depend on constitution, on habit. on unknown varieties of vaccine matter, or unknown va rieties of variolous infection, we have the valuable conso lation of concluding that, in every case of cow-pox "not evidently spurious," the susceptibility is so far subdued ac to secure the individual, in all human probability, from all the dangers, and (it is not unimportant to add) from all the deformities, occasioned by the small-pox. It remains for future inquirers to substantiate a still more select form (31 cow-pox, by which the security will be more perfect. In the mean time, we ought to be thankful for the valuable advantages attending it even in its most questionable form.
These observations are called for by a most important circumstance, the occurrence of an epidemic small-pox in Cupar, in Fifeshire, in the spring of 1817, of which an ac count has been published by the author of the present ar ticle, founded on inquiries which he made in the form of domiciliary visits, while the circumstances were fresh in the memories of the parents of those who had recovered, and while some patients still laboured under it in its dif ferent stages. From this account we shall take the li berty of extracting some of the leading circumstances.