2 Squire, Trans. Internat. Med. Congress, London, 1881.
3 Clinical Medicine, vol. ii.
4 Archives of Dermatology, Oct., 1874.
5 See especially Kassowitz's paper, "Die Wirkliche Stellung der sogenannten Rubeola," etc., Trans. Internat. Med. Cong., 1881.
ETIOLOGY.—The contagium of rötheln is unknown, but that the disease is contagious has been fully demonstrated by numerous observations of epidemics and sporadic cases. From my own experience I should judge that unprotected persons are not so susceptible of it as is known to be the case under similar conditions in measles;6 yet cases are recorded which would prove that the contagion may be conveyed through a third person and for some distance. It is probable that the vehicles of contagion are the same as in measles. At what period of its course the disease is most capable of transmission has not been satisfactorily determined. Squire is of the opinion, however, that the disease is contagious before the appearance of the rash, and may continue so for some days or for two or three weeks. Rötheln may be called a disease of childhood for the same reason that the other contagious exanthemata are—namely, that the majority of adults have already been attacked. From an examination of available statistics I am inclined to regard the ages between five and fifteen—the years of school attendance—as the period of life most susceptible of the influence of rötheln, although, of course, no time of life is entirely exempt. The non-susceptibility of sucklings, as in measles, holds true as a rule, although I am in a position to supply exceptions to this from my own experience, as well as from that of others. Sex seems to be without influence in determining liability to the disease.
6 In this regard it resembles scarlatina more than measles, for I have a number of times seen the disease introduced into families, where it would attack one or two of a number equally exposed. J. L. Smith regards it as feebly contagious, and quotes Chadbourne's experience to the same effect. Liveing declares that rötheln is more distinctly epidemic in Great Britain than either measles or scarlet fever, although probably less contagious.
The period of incubation is not very definitely settled, and, indeed, owing to the generally trivial character of the affection, evidence on this point is difficult to obtain. Taken as a whole, it is probably longer than is observed in measles. According to J. Lewis Smith, in the epidemic observed by him the incubation period varied from seven, or less than seven, to twenty-one days; Emminghaus places it at from two to three weeks; Thomas, from two and a half to three weeks; Squire, mostly a fortnight, the extreme being twenty-one days; Cheadle, from eleven to twelve days.
There is nowhere recorded a trustworthy instance of a second attack of rötheln, although from analogy such an event is to be expected. As in measles, true recurrences of rötheln—that is, the result of a fresh infection—are not to be confounded with relapses. I have never witnessed a relapse, but cases of such a nature have been recorded by other observers (Lindwurm, Emminghaus, Körtlin, Kingsley).
Rötheln is a disease sui generis, and is in no way related to either measles or scarlatina; that is to say, it is not an irregular form of either of these nor a hybrid of them, nor has it ever been observed to propagate anything but itself. That it is not connected with any of the symptomatic skin eruptions—the so-called roseolæ—is proved by its contagiousness and epidemic character. I quite agree with other observers in declaring that rötheln has very little clinical resemblance to scarlatina, and that, on the other hand, in the greatest number of cases the points of likeness are with measles. In the section on diagnosis the differential points between rötheln, measles, and scarlatina will be considered; therefore in this place it will only be necessary to call attention to certain general facts. Thus, aside from the marked divergence in clinical symptoms—incubation, invasion, fever, eruption, complications, and sequelæ—we are at once met by the positive fact that epidemics of rötheln, while always presenting identical features, prevail without regard to the existence of similar epidemics of measles and scarlatina—following or preceding them—and that attacks of rötheln offer no bar to the reception of their contagions, or vice versâ. Literature is so full of examples of this statement that it need scarcely be dwelt upon. By way of illustration, however, the accurate observations of J. Lewis Smith may be quoted in this connection. Of 48 cases recorded by him prior to May 1st in the New York epidemic of 1874, 19 had had measles. Rötheln in the N.Y. Foundling Hospital in 1873-74 followed an epidemic of measles. During the epidemic of 1880-81 the same fact was observed—namely, that a previous attack of measles, as well as scarlatina, afforded no protection from rötheln. I could multiply such examples from my own experience. A single interesting instance may be noted here. A physician asked the writer to examine his child, suffering, as he thought, from measles. A careful investigation revealed a typical rötheln. A number of weeks later an older child got measles, from which the rötheln patient acquired a characteristic attack of the same. In the following year both children were taken with scarlet fever.
The only escape for those who would deny the autonomy of rötheln is in the bold assertion that both measles and scarlatina more frequently recur in the same individual than universal experience and observation will allow; and this leaves them in the dilemma of determining to which group rötheln must be relegated. The hypothesis of the hybrid nature of rötheln cannot be accepted by the pathologist nor the clinician, if for no other reason than that no one has ever seen rötheln generate anything but rötheln, and in no case give rise to either scarlatina or measles.