CHART I.

WITH

MONTHLY INFANT DEATHS FROM INTESTINAL DISEASES IN MUNICH, 1895-1904. COMPARED MEAN MONTHLY TEMPERATURE 3300+19° JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV

Let us now examine one of Liefmann and Lindemann's1 charts (Chart II), which shows the relation of the daily infant deaths to the daily temperatures in Berlin during the year 1905, which was characterized by some hot weather for that latitude.

According to these authors, in the spring of that year the daily infant deaths were between 15 and 20. Had this rate been kept up throughout the year, some 7,000 babies would have died. As a matter of fact, there were about 10,000 deaths of infants, the excess being almost entirely due to increased mortality in the summer. On certain days the mortality was so high that it was two or three times the norm.

An examination of this chart shows two striking peculiarities. First, two sharp prominences with their apices on the 7th of June

1A careful study of their work is recommended, as well as of Rietschel's comprehensive monograph on this subject. I am indebted to these authors for much of my material.

CHARTTII.

and the 2d of July, respectively, and, second, a high and broad elevation in August, crowned with a succession of smaller secondary prominences.

Liefmann and Lindemann distinguish two elements in their curves, (a) the early summer mortality, and (b) the late summer mortality. Early summer mortality.-On inspection it is seen that there is a striking parallelism between the temperature curve and the mortality. This is especially manifest in the sharp increase in the number of deaths on June 30 and July 1, accompanying the high temperature on those dates.

This parallelism is manifest, not only on the hottest days, but the moderate heat of the 4th and 5th of June, also, is sufficient to provoke an increase in the deaths recorded.

An interesting circumstance, developed from the study of this and other curves in their series, is that, generally speaking, only temperatures of considerable height (22° to 25° C.) are effective in producing an increase in infant deaths. Often the first hot wave does not call forth the expected response.

The late summer mortality.-The late summer mortality corresponds to the high and broad curve of deaths from the middle of or end of July to the last of September. This portion of the chart presents a different relation to temperature than that corresponding to the early summer. The high mortality present in the first part of August no longer recedes to the norm with falling temperatures. On the contrary it remains great in spite of the interpolation of periods of cool weather of some duration. Nevertheless, rises in the temperature are accompanied by an increase in the number of deaths, which serves to give this curve its jagged outline.

The mortality curve in this portion of the summer seems to express the summation of the effects of a long period of warm weather, as a basis, combined with the exacerbations provoked by repeated sudden increases in the temperature.

Curves of a cool year.—If now we examine these curves for a cool year, we find a different set of relations. Chart III shows these conditions during the year 1907, a cool summer with only one hot period in May.

We see, upon examination, a response to the hot weather of the 7th and 12th of May, but, owing to the very moderate temperatures prevailing throughout the rest of the year, the broad midsummer rise in the mortality curve is practically absent.

CHART III.

Character of Deaths in the Early and Late Summer.

The differences in the reaction of the mortality curve to temperature in the early and the late summer is accompanied by differences in the nature of the infant deaths recorded. According to Liefmann

and Lindemann, an examination of the death certificates showed that in the early summer a large number of deaths were recorded with acute symptoms not referable to the intestinal tract.

For instance, of the 88 infants dying on the hot day of July 2, 1905, only 16 died of intestinal diseases, while in 52, or about 60 per cent, the cause of death was given as convulsions, brain stroke, and heart failure, or, in other words, with symptoms mainly referable to the central nervous system.

As the summer progressed, however, the number of deaths from gastro-intestinal diseases gradually increased, so that toward the end of August and the beginning of September from 72 to 78 per cent of the diagnoses on the death certificates gave this class of diseases as the cause of death. Hot days brought an increased number of certificates recording deaths with acute symptoms, and a number of such deaths were found even in comparatively cool weather at this period. A considerable difference in the duration of illness was apparent. In the early part of the summer about 50 per cent of the infants died after an illness lasting only one or two days, while in the latter part only about 20 per cent died with such acute symptoms. The remainder succumbed to illness of a more chronic character.

The following tables from Liefmann and Lindemann give a good idea of the relative frequency of deaths with acute symptoms and from gastro-intestinal diseases in the various parts of the summer (Table 1) and the course of the mortality from gastrointestinal diseases during the summer of 1905 in Berlin. (Table 2.)

TABLE 1.-Causes of mortality during different parts of the summer, Berlin, 1905 (after Liefmann and Lindemann).