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CHAPTER XIV.

Immunity" (exemption) of young infants set down to "diminished susceptibility"—The interpretation offered is that they do not get an efficient dose of the infection.

PERHAPS the hardest problem for the contagionist has been the exemption of young infants during epidemics of measles. It is found that whilst the sucklings and nurslings of the well-to-do classes are rarely affected with the rest of the family, even the sucklings of poorer people not unfrequently go scatheless through an outbreak in the house. As Thomas observes :— -"With children under one year, or especially those under six months of age, measles, in spite of all denial, is decidedly less frequent, as I also can testify on the ground of my own observation. . . The fact of the frequent immunity of sucklings is established."

There was no getting over this; and therefore the exemption of infants had to be rationally accounted for, or to be reconciled with the law of distribution of the contagium vivum. The facts have been elaborately investigated, especially by the German school; and on the whole the conclusion arrived at is, probably, one of the weakest in all etiology. The statistics collected to determine the relative number of deaths from measles of infants up to the age of three months, and from the third to the sixth, from the sixth to the ninth, and from the ninth to the twelfth month, a summary of which is given in Thomas's article in Ziemssen, show a little variation in the return from different districts; but the broad results brought out are that infants up to the sixth month are rarely attacked with measles, but that then they become month by month more and more liable to attack,

and just before they are yearlings they are more frequently attacked, and the mortality amongst them is greater, than between the age of one and two years. Thomas says that their early immunity "admits of a twofold explanation; it may depend upon diminished susceptibility, it can, however, also be the result of less opportunity for the reception of the contagion. This last is especially the case when the suckling is the only child in the family, but by no means explains the increase of the frequency of attack in the separate stages of the first year of life. This is rather to be explained by an increase of susceptibility to measles towards the conclusion of the first year. Sucklings then possess no immunity from measles, as is stated in many reports. Their susceptibility is, however, indubitably less. The following figures may serve as proof. . . . Accordingly, no further doubt can exist with reference to the diminished susceptibility of nurslings, to which, according to Rilliet, Ackermann had already called attention at the end of the eighteenth century, and which near the first year of age rapidly disappears." (The italics are mine.)

The interpretation of the phenomenon of the non-occurrence of measles in these infants by means of the supposition of diminished susceptibility might have been clearer and more satisfactory if one had been told, or if one knew of, or could imagine, any inherent or innate force in the youngest sucklings, by which they are enabled to resist successfully the morbific action of a contagium against whose effects they are utterly helpless when a few months older. Why a change should come over the infant, converting its original condition of diminished susceptibility into a state of the highest receptivity is certainly not evident; yet figures are furnished as proof that this metamorphosis does actually take place. The law of early immunity is not, however, fixed and immutable; even the tenderest infants are not invulnerable. Thomas says:-"Individual observations, however, inform us that even the youngest children are not entirely without any predisposition. Heim reports measles in a child of four days." [Similar instances of a tendency to retrogression are given.] "Consequently children

can be born possessing at once a decided susceptibility for the contagion of measles."

This grave assurance that the newly-born are not, of necessity, measle-proof-that they can actually be born in such a defenceless condition that they cannot ward off the effects of a dose of the measles poison when they get one-is one of the most curious passages in modern treatises on medicine. As it cannot be supposed that this great authority is trifling with the subject, or that he has not propounded his solution of the problem of the exemption of the younger nurslings and sucklings in good faith, future investigators probably will hardly know which to wonder at most the marvellous conception of the etiologist, or its quiet acceptation by the faculty. However, when we find a contagionist driven to frame and other contagionists fain to adopt such an exposition of an easily read phenomenon as this, it is not difficult to see that the non-infection of the youngest infants seriously affects the tenets of the doctrine of contagion -that it goes far to upset the theory that the contagium of measles is a volatile and diffusible something, one particle of which is sufficient to cause the disease. It is an awkward fact that this unknown infective agent, which wanders everywhere and clings to everything about a house, and infects instantaneously all other children in it, should fail to infect the infant of the family for the first six months of its life. Indeed it seems almost impossible to reconcile the escape of these youngest sucklings and nurslings with their environment by an atmosphere holding abundance of contagium vivum. The difficulty could have been got over only by some such ingenious supposition as that of diminished susceptibility. Bewildering and hardy as it was, it was perhaps the nearest approach to be had to a reconcilement of the facts with the doctrine.

The "straw mildew theory" takes in the facts and explains them clearly and fully. Instead of looking to degrees of susceptivity corresponding to the separate stages of the first year of infancy (and if we looked closely we should assuredly find that the law relating to vulnerability in this matter has been boldly inverted to suit the occasion); instead of piling up figures

and collecting statistics, the real question to look to is whether the youngest suckling is on an equal footing, in regard to its exposure to infection, with the other children in the house. Does it get the same or an equivalent amount of measles poison? It will be observed that Thomas just touched this question, but either failed to grasp it firmly or elected to drop it advisedly.

In saying that the immunity of infants might "also be the result of less opportunity for the reception of the contagion," he shows that the common sense view of the matter had presented itself; but that, whether for the reason that it could not well be brought to accord with the conception of contagion, or because the notion of a sliding-scale of susceptibility was too captivating, it had been dismissed.

From the data extant it is an inference easily reached that young infants remain uninfected for the simple reason that they are not left at night, except in the lowest walks of life, to breathe the air of the bedrooms of the infected children. The suckling is rarely submitted to the same conditions as the rest of the family. As a rule the mother takes it to her bedroom and puts it to sleep on a pillow or in a cot, or takes it to bed with her according to circumstances. These infants, therefore, are seldom exposed to what has been here called efficient contamination. It is unnecessary to enlarge upon those domestic arrangements in families in different ranks, from which it comes that the suckling is gradually resigned more and more to the custody of a nurse, or of an older child, and by degrees eventually arrives at a stage when it is exposed to the measles poison equally with the other children, and is infected with them accordingly. The sudden augmentation in the rate of the mortality of infants from measles, and the thenceforth steady increase in the rate, correspond pretty closely with the changed conditions to which they are submitted. As with older children and adults the efficient infection of the infant, as I conceive, turns upon its getting a sufficient dose of the poison; and its exemption is fully explained by its not getting it.

CHAPTER XV.

Epidemics in certain islands held to be proof that measles are communicated from person to person solely by contagion-The epidemic in Fiji-Former views in regard to it-Extracts from Miss Gordon Cumming's account of the visitation-Mild attack of Cacobau and his sons contrasted with the subsequent virulence of the diseaseVirgin soil"—Uniformity of the epidemic points to similarity in the infection-Faröe Islands.

SOME islanders and natives of tropical regions are exempt from measles unless the disease is introduced into their countries by the infected. Measles may be said to be endemic only in temperate and sub-tropical regions; and this limitation corresponds with the geographical distribution of the cereals.

No arguments are used so frequently and so triumphantly to prove that measles are caused and propagated solely by contagion as those derived from the well-known fact that certain islanders have been scourged with epidemics of this disease after its introduction into their islands. The fact that the outbreaks occurred as a consequence of the importation of the infection being indisputable, etiologists and epidemiologists fasten on to it and adduce it as proof positive of the soundness of the doctrine of contagion and all that it entails. It is held to establish the view that the only way in which measles can be disseminated is by a transmission of the contagium from person to person. It is considered to be a complete and decisive settlement of the question once for all. There is no getting over it or going behind it. As is the case, however, with many other facts relating to the occurrence of infective disease, this fact will bear another interpretation.