average temperature is less; and, in general, that the number of deaths from these causes is directly proportional to the elevation of temperature, especially if it be long continued. Thus, of 3,216 deaths from the diarrhœal diseases in Vermont, New Hampshire, Massachusetts, Rhode Island, and Connecticut in 1883, 2,745, or eighty-five per cent, occurred during the months of July, August, and September. The same States showed an increased mortality from these causes during the unusually hot summers of 1880 and 1882. In the city of Boston, for the nine years from 1867 to 1875 inclusive, the mean temperature of the months of July and August varied from 68·6° in 1874 to 72·3° in 1870, and averaged 70·5°. The highest death-rate was in 1872, when the mean for the two months was 71·9°, and for the hottest single month was 73·1°; and the lowest was in 1867, with a mean for the two months of 69·8°, and for the hottest month of 70·4°. In New York, during the month of July, 1872, the mean temperature was 79·57°, or 3·43° higher than the average for the ten previous years. As a result, the mortality for the quarter was the highest ever known in the city, and that notwithstanding that the other two months were not unusually hot.
It must be stated that, fatal as is the effect of heat upon children under five, the proportionate mortality is still greater when the investigation is limited to infants under one year of age. Dr. Blackader says that a very hot summer month will triple or even quadruple the mortality of infants under one year, though that of children from one to five is barely doubled. During the year 1872, in New York, nearly sixty per cent of all deaths were under one year of age, and more than forty per cent took place in the summer quarter.
The effects of improper feeding are seen in the fact that, whether in city or country, in hot summers or cool, only a very small proportion of deaths from infantile diarrhœa occur among infants who are properly nursed upon the milk of a healthy mother—which must be considered the only natural and proper method of feeding young infants.
Sir Hans Sloane showed years ago that the mortality of those properly nursed upon breast-milk was to that of those who were bottle-fed as 19·2 to 53·9 per cent. Dr. J. Wilmarth reports that in a country practice in Massachusetts, out of one hundred and one children nursed wholly, or nursed and fed with nursing after a few months to weaning-time, and who were under his observation for a series of years, there were twelve deaths from various causes, none of them from cholera infantum; while among nineteen children artificially fed, there were during the same time eight deaths, six of them from cholera infantum. Says Messener: "Cholera infantum attacks only those children who have been