Theory of the nature of Smallpox.
The nature of the disease should, however, be borne in mind always in the front of every speculation as to the origin of its contagious and epidemic properties. It involves no speculative considerations to pronounce smallpox a skin-disease, of the nature of lichen turned pustular. It is a skin-disease first, and a contagious or epidemic malady afterwards; its place among diseases of the skin is indeed fully acknowledged by dermatologists. Apart from its contagiousness it conforms to the characters of other cutaneous eruptions: its outbreak is preceded by disturbed health, including fever; when the eruption comes out the fever is so far relieved; and as in some other eruptions which are not contagious the constitutional disturbance is in proportion to the area of the skin involved. Even the peculiar scars or pits which it leaves behind in skins of a certain texture or in the more vascular regions, such as the face, are not unknown in non-contagious skin-diseases; nor does its other peculiarity, the offensive odour of many pustules, seem unaccountable in a skin-disease native to tropical countries.
Eruptions on the skin are in many cases the outcome of constitutional ill-health; for example, the eczema of gout. Also where the whole body is infected, as in syphilis, there are skin-eruptions, which may be pimples (lichenous) or scales, or rashes, or, as in the first great outburst of syphilis, “pustules” so general over the body that those who were casting about for the nosological affinities of the new malady, saw no better place for it than Avicenna’s group of alhumata, which included smallpox and measles. That a skin-eruption of the nature of smallpox should have come out as a constitutional manifestation, and that a number of persons should have exhibited it together for the same internal reason, are both credible suppositions, although necessarily unsupported by historic evidence. Let us suppose that the Abyssinian army before Mecca endured some ordinary discomfort of campaigning, that, in the uniformity of their life, numbers together had fallen into the same constitutional ill-health just as numbers together have often fallen into scurvy, and that an eruption of the skin, proper to the tropics, was part of it. What we have farther to suppose is that the constitutional eruption became catching from the skin outwards, so to speak,—that it could be detached from its antecedents in the body, and could exist as an autonomous thing, so that it would break out upon those who had none of its underlying constitutional conditions, but had been merely in contact with such as had developed it constitutionally or from within. Such detachment of a constitutional eruption from its primary conditions is little more than constantly happens when a skin-disease like eczema, or acne, persists long after its provocation, or the disordered health which called it forth, is removed. The inveteracy or chronicity of some skin-diseases is itself a form of autonomy, but a form of it which does not transcend the individual, just as, among infections themselves, cancer does not transcend the individual or propagate itself by contagion[872]. But there exists a closer probable analogy for a secondary eruption becoming a self-existent or independent infective disease. The instance in view is no more than probable, and may easily be disputed by those who have sufficient prepossessions the other way; but there is no theory that suits so well the negro disease of yaws as that it is a somewhat peculiar secondary of syphilis, which is now able to be communicated as an exanthem detached from the primary lesions on which it had depended originally for its existence.
All the evidence, historical and geographical, points to the several varieties of the black skin (or yellow skin) as the native tissues of smallpox. It is not without significance that a disease of the negroes which was observed by English doctors not long ago in the mining districts of South Africa led to a sharp controversy whether it was smallpox or not: according to some, it was a constitutional eruption; according to others it was a contagious infection. Such phenomena are not likely to be seen in our latitudes; but the original smallpox itself was not a disease of the temperate zone[873].
I shall not carry farther this line of remark as to the probable circumstances in which a pustular eruption, among the Abyssinians before Mecca, or among other Africans or other dark-skinned races in other places and at other times, had become epidemically contagious in the familiar way of smallpox. One has to learn by experience that there is at present no hearing for such inquiries, because a certain dominant fashion in medicine prefers to relegate all those origins to the remotest parts of the earth and to the earliest ages (practically ab aeterno), and there to leave them with a complacent sense that they have been so disposed of. That is not the way in which the study of origins is carried out for all other matters of human interest. Yet diseases are recent as compared with the species of living things; some of them are recent even as compared with civilized societies. Epidemical and constitutional maladies touch at many points, and depend upon, the circumstances of time and locality, and upon racial or national characters. Perhaps their origins will one day be made a branch of historical or archaeological research.