We now come to a comparison of these opinions with the statistics of the Registrar-General, bearing well in mind, however, the probability of this disease having undergone a great modification since the introduction of vaccination by Jenner. The mean of the last ten years proves that the small-pox is the most fatal (this does not always imply most prevalent) during the winter, the average number of deaths from this cause being as follows:

Winter 226 | Spring. 221 | Autumn. 217 | Summer. 208

It must be observed, that the range between 226 and 208 is not a very extensive one, and certainly not a sufficient one on which to form even the vaguest aphorism. The reader will recollect, that the epidemic small-pox, whose history Sydenham so elaborately wrote, succeeded the plague. In 1854, London was again visited by the cholera, and it is remarkable that during the three first seasons of the year the number of deaths caused by small-pox were considerably below the average of the last ten years, but that during the last quarter it rose considerably above it, the weekly returns beginning to swell considerably after the forty-third week, the last in October, when the deaths from cholera had fallen to 66. In 1849, the cholera seemed to have been preceded by the small-pox, for the year 1848 was remarkable throughout for the high rate of mortality from this cause. The constitution of the last year was certainly peculiar and eminently pestilential. The months during which the small-pox was most virulent were characterised by the presence of a great amount of ozone in the atmosphere, and the prevalence of the equatorial winds. Thus, the average daily amount of ozone was, during

October. . 4.8 | November. . 47 | December . . 11.8

The temperature both of October and November were respectively 20 and 3° below the average. The greatest mortality from small-pox took place in December, and was coincident with

2°

excess of ozone, high westerly winds, and a low barometer, which was 0.120 in defect of the mean of seven years.* The epidemic constitution of the air in its relation to small-pox has frequently been the subject of inquiry, but at present we know little more than that, at certain periods, this disfiguring scourge goes its rounds, and that frequently, during its visits, there are present many meteoric phenomena, which are known to be the accompaniment of a pestilential state of the atmosphere. We can easily imagine that a zymotic disease, capable of impregnating the air to the extent of several feet in the vicinity of the patient suffering from it with poison-germs,―might, under some peculiar combination of the elements of the atmosphere, be capable at times of disseminating its invisible ferment with concentrated power, the air as it were being, for the time, congenial to its life, and giving an impulse to its activity,—just as we see how the feathery seeds of some plants will pass over large tracts of land, and, as they drop one by one into the soils over which they are wafted, they either die and leave no record behind them, or else spring up and luxuriate in some far-off land, rejoicing as it were in having found at last a home congenial as the one from which winds had carried them. The air is too often the soil in which the seeds of disease germinate, can we not follow up the analogy a little farther, by imagining such a thing as a rotation of diseases? We know that, in farming, certain crops exhaust the soil in which they are cultivated, and, if continued year after year without a change, at last degenerate so as to become almost extinct. May not epidemics exhaust the atmosphere of those peculiar elements on which they feed in a similar manner? or may not their mobile bed be changed, so as no longer to afford them the means of existence?

Diseases, like plants, may be classed into annuals, evergreens, and deciduals. The last are those which almost entirely disappear at certain seasons, but which as certainly reappear as the

* The Weather of 1854, published in the Times, January 17, 1855, by E. J. Lowe, Esq.

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seasons themselves do,-let diarrhoea be a type of this class. Then we have the evergreen phthisis, with its steady mortality throughout the year; and lastly, the annuals are those epidemics which flourish for a season in a certain district, and, when they have racked out the soil in which they grow, decline and disappear, until some other epidemic has prepared the air for their reception. We know that many diseases follow each other in regular order, and, as one declines, another springs up and flourishes as it were on the ashes of its predecessors. We are ignorant, however, so far, of the nature of these invisible diseasemanures, which foster the handmaids of death; and, even did we possess the knowledge that we confess we lack, it would be of little use unless we could control it, like the agriculturist does his soils, who, by experience and scientific cultivation, can render his land, at the same time, favourable to his crop and inhospitable to weeds.

During the years that the small-pox raged epidemically in England, no peculiar state of the atmosphere was particularly noticed. Although it often began in winter, and reached its height in summer, yet did the heat, dryness, frost, moisture, and the winds, and the height of the barometer, give no clue to its atmospheric source. Epidemic years have been observed, however, to be most favourable, not only to its greater prevalence, but to its greater fatality. Since, however, this disease seems to be more controllable through that blessing, Vaccination, than most other epidemics with which we are afflicted, it is to be hoped that the extended investigations in the study of meteorology, and its relation to disease, will eventually guide the profession to the discovery of those laws which appear to regulate it in the epidemic form.

The Mortality from Small-pox in London.

In 1852 the small-pox was particularly virulent: it began to be so in the last quarter of the preceding year. Thus: :

On referring to the Tables where small-pox, measles, scarlatina, and typhus, are traced, we are at once struck with the fact that throughout the year small-pox pursues a much more equable course than either of the other three zymotic diseases. The years 1844 and 1848 were also remarkable for the mortality from small-pox exceeding that of former and later years: the epidemic of 1844 was both preceded and succeeded by years in which measles were unusually fatal. Small-pox appears to be less influenced by the variations in the weather from week to week than the other three diseases. This will be evident on examining the Tables where its course is traced. Were the subject more narrowly studied, it might be discovered, perhaps, that each disease has its own peculiar mode of fluctuating. Some, for instance, as Cholera, rise suddenly like a gigantic wave once in the year, and fall as rapidly as they rise: the wave of others may be seen to swell towards a certain season, and then decline: carrying with it, however, a number of smaller ones, which seem to be dependent on the weekly variations in temperature, wind, and other weather influences. Viewing the fluctuations of disease then in this light, we may describe the disease-wave as having a valley and a crest: the latter indicating when it is most fatal, and the latter when it is least so. The pulmonary diseases generally have two waves in the course of the year; the valley pointing to the warm summer months, whilst their crests are directed towards the latter end of autumn and the early weeks of winter. Phthisis, however, like small

pox, pursues the even tenour of its course throughout the year, dipping gently towards the more genial summer to rise again in the autumn, and reach its acmé in the succeeding spring. The waves of scarlatina and typhus begin to rise in the spring, and reach their greatest height about the beginning of autumn. Cholera leaps suddenly like a gigantic mass of water thrown up by a submarine volcano, with no smaller fluctuations, culminates in a few weeks, and falls as rapidly as it rose. Were maps of diseases which extend over a great number of years placed side by side in a continuous line, I have no doubt that a practised eye could recognise any epidemic by the peculiar fluctuations which it is in the habit of making.

Measles.-On reference to the Table which represents the statistics of deaths from measles, it will be found that in the year 1854, when small-pox was least fatal-namely, in the spring, rubeola slew 476 persons in London, and that when this disease began to decline in the succeeding summr, variola showed a tendency to rise in the scale of mortality, and continued to do so until it arrived at its maximum during the autumn quarter, when it exceeded the mean quarterly average by 72 deaths, while measles had subsided at the same period to within four or five of the mean for ten years. If we take the mean just alluded to, the relative mortality of measles during the four seasons will thus appear :-Autumn, 364; Winter, 284; Spring, 277; Summer, 270. Whilst for 1854 the order would be somewhat different. Thus: Spring, 476; Autumn, 369; Winter, 344. Summer, 210. The Small-pox Tables show a deficiency in the number of deaths from this disease during the summer months, July, August, and September, the period of the visitation of the cholera, which by the 30th of September had destroyed 9,707 persons. From these facts it will be evident to the student how the even tenour of regular epidemics is interfered with by the grander scourges which every now and then sweep through the habitations of man.

Some are of opinion that the measles often introduce small