In warm weather, such as we have in summer, high humidity coupled with high temperature is very harmful, as is shown by the extreme death-rate in Japan during August and September, when the hot, humid summer produces its full effect. On the other hand, ex treme dryness is also harmful in summer. Some of the worst colds, especially those of a catarrhal nature, come from extreme dryness in hot weather. Oddly enough the effect of hot and cold weather is in some respects the same, for both increase nervousness and make the mucuous membranes sensitive, thus giving bacteria a chance to grow.
How to Remedy Indoor Dryness in Winter.—In winter such desert like dryness is very common inside our houses and is one of the great reasons why our work falls off and disease and death increase in the community. By heating our houses we successfully overcome the effect of low temperature, but at the same time we make the air so dry that it is very harmful. In spite of the common idea to the contrary, a damp winter month with an average temperature of for example, is more healthful than a dry one of the same temperature provided the dampness is not too monotonous. Hence every wise householder takes pains to see that there are large water pans in the furnace and that they are fitted with wicks or other devices for giving a large surface for evaporation. Or if steam or hot water is used for heating, he puts on the radiators some device such as pans of water with cloths suspended in them so that they draw out the water and cause enough to be evaporated to raise the relative humidity in the house to at least 50 per cent and preferably 60 per cent or 70 per cent, if this does not cause wet walls, instead of 30 per cent or less, as is now the case in cold weather. When this is done, the temper ature can, and must, be kept between and where it belongs, for moist air feels warmer than dry air at the same temperature.
The Optimum Variability.—A climate may be ideal in tempera ture and in humidity, and yet be by no means the best kind. This is because all living creatures seem to need change. If animals are fed absolutely the same food day after day they do not thrive nearly so well as if their food is varied. So, too, if plants are kept at the optimum temperature day after day, they will not grow so well as those which enjoy first a warmer and than a lower temperature. Man is also extremely sensitive in this respect. In general a rise of temperature harms him and a drop stimulates him, but a combina tion of frequent changes in both directions does him much more good than uniformity. In New York City, for example, a drop in tem
perature causes an increase in people's activity both in summer and winter and a corresponding drop in the death-rate.
Why a Drop in Temperature is Beneficial.—It is easy enough to understand how a drop of temperature is beneficial in summer, for then it causes an approach to the optimum. In winter, however, the drop takes the temperature away from the optimum. How then can a cold wave be helpful? It seems to act in two ways: (1) When people are out in the air while the temperature is falling it acts like a cold bath. Unless the change is too great it increases the rapidity of the circulation causing a healthy glow. (2) When people are within doors a drop of temperature in winter is stimulating because it causes the air inside the house to vary in temperature. The furnace fails to preserve that uniform temperature which so many people wrongly suppose to be desirable. Thus the rooms become first a little cool and then grow warm, giving variations which are beneficial to health.
Why Cold Spells are Harmful.—While a cold snap is beneficial, a cold spell is harmful for three reasons: (1) The air in the house maintains a nearly stationary temperature. (2) It becomes ex cessively dry. (3) People keep their houses too warm. This is because the extreme dryness of the air makes them feel chilly, for it causes rapid evaporation from the skin. Even a moving door causes a perceptible and chilly draft. Hence the furnaces are pushed to the limit, and people who feel comfortable at in the fall now want a temperature of to These three conditions make people feel stupid, nervous, and cross; many catch cold or suffer from headaches; others become sick; and the community suffers more than the usual number of deaths.
Why Cyclonic Storms are So Helpful.—Changes in other respects as well as in temperature are highly desirable. For instance, steady sunshine is not nearly so good as a of sunshine and then one of clouds and rain. But too much cloudiness also leads to ill health and to inefficiency. What is needed is frequent changes of all sorts, not too extreme, but quite frequent. For this reason the countries in the regions of cyclonic storms are particularly fortunate. They enjoy changes of weather every few days.