PATHOLOGY 403 developments of those catarrhal epidemics which we meel with on a homely scale within single households. Another example of the same kind of communicability of a simple catarrhal affection of a mucous membrane is the Egyptian form of "cold in the eye" or ophthalmia, which was brought to England by a few of the troops returning from the expedition of 1801, and which spread by contagion for several years through the home-garrisons with a viru lence quite unknown in the Egyptian climate, so that more than two thousand soldiers had to be pensioned for total blindness due to it. lies In such instances a common and, it may be, trivial 1 s " malady becomes a species of disease ; it acquires the remarkable power of reproducing itself in persons who had not been exposed to the primary exciting causes. Not one in a hundred of the soldiers who were blinded by ophthalmia during the first ten years of the century had ever been in Egypt, just as, in a household where catarrh has become prevalent, perhaps not more than one member of it had sat in a draught, or been caught in the rain, or otherwise been subject to the conditions that ordinarily bring on a common cold. It is the acquired catarrhal condition that spreads from person to person, being faith fully reproduced in each new victim. The morbid con dition becomes a kind of individual thing, of which the seminal particles are scattered abroad and induce the same morbid condition where they find a favouring soil or a favourable lodgment. If all the instances of infection could be reduced to the same category as these, we should simply have to regard the specific infective diseases as the spreading or com municable forms of morbid conditions of the body other wise accounted for as states of disease leading a kind of independent life, but traceable in the last resort each to its origin in certain structural and functional errors of the body. The great problem of the species of disease would thus become an evolutional problem. While this evolu tional problem would always have underlying it the unique difficulty of conceiving how a morbid state of the body could be integrated to become a semi-independent exist ence, with the power of reproducing itself by its germs as in the generation of living things, the interest for each specific disease would be to follow up, historically, geo graphically, ethnologically, sociologically, and otherwise, the conditions of body out of which the complex natural history of the disease-species had grown. Proceeding, then, in the natural -history manner, and attempting, in the first instance, a grouping of the species of disease, the broad lines of division are into the chronic and the acute, and, among the acute themselves, into exo genous and endogenous.
- en- Acute Infective Diseases Exogenous and Endogenous. The endo-
i mil genous species of disease are those in which the infecting particles |c gen- pass directly from the sick body to the sound, giving rise in the i .cute latter to a morbid state which follows the same order of unfold- ses. ing, and attains the same type as in the former. The exogenous species of disease are those in which the infecting or germinal particles have an intermediate state of ripening in the soil, or in water, or amidst other favouring conditions, producing a definite set of morbid phenomena in the exposed body, but a set of pheno mena which may be, and often are, different in important respects from those of the primarily-ailing subject. These contrasts between the endogenous and the exogenous infections may be illustrated by a reference to smallpox on the one hand and to cholera on the other. Any person whose skin is covered with the drying crusts of smallpox pustules may give off infecting particles which will set up the same disease if they find a lodgment in a susceptible person, the contagiousness of such a case of smallpox being some what heightened, no doubt, by a close atmosphere and the like. But for cholera, speaking generally, much more than this is wanted for the development of the communicated disease ; the infecting particles have in most cases to undergo an intermediate stage of ripening in the soil or in other outside media. Yellow fever is even more than an exogenous infection ; it is also vicarious, inas much as, over and over again, it has been from the emanations of dysenteric dejecta of the negro (who can hardly take yellow fever), and not necessarily from the effluvia of pre-existing yellow fever cases, that the infective power has proceeded. The vicariousness of yellow fever brings it into close relation with typhus fever, which Typhus is not otherwise counted as an infection of the exogenous group, fever. No attempt to trace all cases of typhus to pre-existing cases of the same fever can possibly succeed ; the succession has been broken repeatedly, and repeatedly started anew, amidst well-known circum stances of cold, hunger, filth, and general misery. In the larger proportion of typhus cases it is the miserable themselves who have suffered from the disease in addition to their other miseries ; but there are numerous classical instances in which the more wretched of mankind have imparted typhus to their more comfortable fellows without themselves exhibiting the symptoms of the disease. The best-known historical cases are the Black Assizes, when prisoners who were brought into court from filthy dungeons so tainted the air of the court-house that the judges, the members of the bar, the jurymen, and the public were seized with a virulent typhus infec tion. If, in such cases, it should be contended that the prisoners carried the specific effluvia of typhus about their persons, although they themselves did not suffer with the specific symptoms of the fever, there are other cases where such a contention is entirely in admissible. Perhaps the most remarkable of these is the case of the Egyptian ship-of-war which brought an epidemic of typhus to Liverpool in 1861. (Epidcm. Trans., i. p. 246, 1862.) More usually, however, it is the miserable themselves who first develop this morbus miserix, afterwards communicating it to the physicians and others who enter their dwellings or otherwise come near them. The de novo development of the symptoms of typhus, and subsequently of the independent contagion of typhus, has been abundantly illus trated in the naval and military history down to the close of the Napoleonic wars. The writings of Huxham, Lind, Pringle, D. Monro, Blanc, and others, who served in the great typhus period, are full of evidence of that kind ; the doctrine of the continuous reproduction of the typhus virus always from pre-existing cases is a purely academical affair, which dates from the ingenious dialectic of Bancroft s Essay on the Yellow Fever, &c., 1811. The rational doctrine of this kind of infective disease, based upon the practical experience of all times, is that which is stated by Pliny : Prime, temporis ac loci vitio, et segri erant et moriebantur ; postea, curatio ipsa et contactus rcgrorum vulgabat morbos " (xxv. 26). Relapsing Fever. Closely related to typhus in the circumstances Relaps- of its origin is relapsing fever, which has extremely slight power of ing fever, spreading among the well-to-do. Its synonym of famine fever is on the whole a sufficiently accurate designation of its circximstances of origin. Its more recently -acquired synonym, spirillum fever, is derived from the presence in the blood of a minute spiral living organism, as to which the standing question arises whether it is there because the particular state of fever is favourable to it, or whether the fever is there because the organism has, for some reason, invaded the body. Here, again, the conflict arises between academical dialectic and the more tangible facts of experience. It is maintained that relapsing fever can be given to the monkey by injecting the spirilla ; but that circumstance by no means serves to show that the pre-existing cases of relapsing fever had occurred because spirilla had invaded the bodies of a certain number of persons. Relapsing fever is sometimes, though rarely, conveyed by infection to those who had not been living in a state of over crowding and of semi-starvation ; and such an incidence of the disease is so entirely arbitrary that even the spirilla, if they came from other cases, might be accepted as the active agents. The spirilla would have a real interest if it could be shown that they could initiate relapsing fever proprio motu. As the case stands, the predisposing causes of relapsing fever completely overshadow all other elements in the causation. The disease is always and every where morbus pauper um, and very often it is typhus famelicus. Typhoid fever. This fever holds a peculiar place in the history of Typhoid, specific diseases. It is unquestionably a far more common disease at present than it was fifty years ago, and it is certain that it was prevalent in Paris for some time before it began to occur, except as a rarity, in London and Edinburgh. The evidence of Christison and of other highly observant pathologists may be implicitly accepted ihat, while Louis and others in Paris were finding ulceration of
- he small intestine in fatal cases of typhus -like fever, no such
esion was ordinarily found in the Edinburgh practice. More generally, it may be said that typhoid fever has been a prominent actor in the mortality during the periods when typhus has been an insignificant one. The coincidence of decided typhoid years with the cholera years is perhaps irrelevant. But there can be ittle doubt that there is a close connexion between the rise of
- yphoid and the more or less considerable diminution of intermit-
- ent fever ; there is indeed much evidence in a certain number of
ocalities in favour of the opinion of Boudin, that malarial fever and
- yphoid fever are mutually exclusive in a given place.
Typhoid fever is undoubtedly a disease associated with the nanner of disposal of human excrement. Whether the typho-
