merable indirect effects through inheritance and material resources. In this he appears to be like all other organisms. For every species of living being there is apparently a certain optimum or most favorable condition. As the temperature, humidity, or other climatic elements depart more and more widely from the optimum, the animal's reproductive rate diminishes, its general strength declines, it becomes more susceptible to disease, and its life is shortened. Between the optimum conditions and those which cause death there may be a wide range in which life and even health are possible, but in which the organism is not at its best. One of the great lessons of biology is that man's physiological nature is essentially the same as that of the lower animals. A law which applies universally to them applies also to him. This is eminently true in respect to climate. By measuring the rate of reproduction of infusoria, the rate of growth of plants, the amount of oxygen consumed by crayfish, or the length of life of the boll weevil we can arrive at an exact estimate of the effect of climate upon these various organisms. In the same way we can measure man's response to climate and find out just what conditions are the best and how much harm is done by departures from the ideal. Thus far man's physical relation to climate has been tested chiefly in the following ways: (1) by frequent measurements of the weight of healthy persons or of those suffering from tubercular or other diseases, (2) by daily or weekly tests of people's strength, (3) by examination of the amount of work done by specially chosen subjects or by piece workers in factories day after day throughout long periods, (4) by measuring the amount of carbon dioxide given off in the breath of people who are at rest under various climatic conditions, (5) by tabulating people's estimates of their own feelings of comfort or discomfort at different temperatures and humidities, and (6) by ascertaining the number of deaths at different seasons of the year and comparing them with the weather. All of these methods yield substantially the same results. So far as temperature is concerned they indicate that people's health is best and their physical energy greatest when the average temperature for day and night together is from 60° to 68° F., which means when the noon temperature ranges from about 65° to 75°. Among the methods mentioned above the study of deaths seems to be the best thus far employed. As this method has never before been used on a large scale, it may be well to consider it somewhat fully. Death is one of the few occurrences which takes place in all parts of the world and can easily be reduced to accurate statistics. Such statistics are kept by all of the more advanced governments, so an enormous body of valuable facts is easily available, and needs only to be tabulated in order to give most significant results. Accordingly, I shall here give a résumé of the detailed study of about 9,000,000 deaths in Italy, France, and the United States, and of the more cursory but no less exact study of a much larger number in Belgium, Germany, Sweden, Finland, and Japan. The most important result of these studies is a series of "climographs" like Figures 31 to 33. Figure 31 is based on 2,500,000 deaths in the part of the United States north of the fortieth parallel and east of the Missouri River during the years 1900-1912. Figure 32 is based on 2,200,000 deaths in France from 1901 to 1910, and 1,500,000 in Italy from 1899 to 1913. Figure 33 is based on 142,000 deaths in four California cities, namely, San Francisco, Sacramento, Los Angeles, and San Diego, from 1900 to 1912. The diagrams show to what extent the deaths during months with any specified temperature and humidity fell short of or exceeded the normal. Temperature is indicated at the left and humidity at the top. The heaviest shading means that on an average the deaths during months having the conditions included within its area were at least 10 per cent |