Geophysical Factors Involved in Bioclimatology.
It would be appropriate at this point to discuss in detail the specific components of climate which are known, or have been claimed, to exert biological effects. However, this aspect of the problem will be treated cursorily because of shortness of time and even more for lack of convincing knowledge.
Temperature and humidity are of course the two climatological factors which are best understood. At their simplest their biological effects are illustrated by the close connection that exists between air temperature and the tempo of a cricket's chirp. It is said that counting the number of chirps in 14 seconds and adding 40 will give the temperature within a couple of degrees. Likewise, the higher the temperature, the faster ants move. As example of more complex effects oftemperature, one could quote the discovery by Dr. Andre Lwoff (reported at the present meeting of the Academy by Dr. Albert Sabin) that a difference of 20C can bring about the selection of virulent or avirulent mutants of polioviruses.28 On the other hand, temperature and humidity have also less direct consequences by reason of the physiological responses that they elicit in living things. In the case of man, his semitropical origin is reflected in the narrow range of atmospheric environment to which he is adapted in his native biological state. Any departure from this environment is likely to cause physiological disturbances. A temperature of 29.40C (850F), with moderate humidity and low air movement, seems best for human comfort in the absence of housing and clothing. In practice, these artificial aids supplement several physiological mechanisms which permit a fairly wide range of adaptive heat control. Thus, enormous changes in blood flow through the skin capillaries can occur within a few minutes and regulate heat loss upward or downward as needed. When increased blood flow proves inadequate for rapid cooling, the sweating mechanism comes into play and provides heat loss by evaporation. While the needs for temperature control are more prolonged, for example in cases of passage from one season or one country to another, the body can regulate its own heat production through changes in metabolic rates. Needless to say, these regulatory mechanisms are effective only within a limited range and, furthermore, any excessive demand on them will cause profound physiological disturbances. In fact, as already mentioned, there is an enormous amount of clinical evidence that weather changes are commonly associated with exacerbation of many disease states. As Hippocrates said 2,000 years ago, "It is changes that are chiefly responsible for diseases, especially the greatest changes, the violent alterations both in the seasons and in other things. But seasons which come on gradually are the safest, as are gradual changes of regimen and temperature."
Contrary to common belief, it has not yet been shown that pressure changes per se can affect either the comfort or the health of man-except of course in the special cases of life at great depths or high altitudes. It may be worth mentioning at this time, however, that very slight reductions in pressure have been shown to exert profound effects on insect behavior, effects which appear to be independent of oxygen tension. In the laboratory, as well as in the field, the feeding habits, rate of development, and locomotor activity of higher insects are appreciably increased by slightly lowered or falling pressures. These conditions also seem to be associated with the sudden occurrence of mass emergencies.29
Needless to say, there is no general statement that can serve to describe the multifarious biological effects of the various types of radiation. Their deleterious effects go from reversible lesions in the skin to the production of lethal hereditary defects. Their beneficial effects range all the way from the synthesis of vitamin D to the orientation provided by polarized light for the motion of insects. The use of artificial light to prolong and increase egg production denotes profound influences on the endocrine system, and this becomes manifest also in bird migrations and in many other complex biological processes.
Recently, experiments with cosmic rays and their secondaries have pointed to the existence of even more profound hormonal effects of radiation. Whereas no clear evidence has been obtained that ordinary cosmic rays have any biological activity, cosmic ray shower electrons (produced by cosmic ray particles that penetrate into heavy matter) were found to increase mutation rates in a fungus, to interfere with normal reproduction in rabbits, and to accelerate the rate of development of cancers in mice pretreated with 20-methylcholantrene.30
Among other climatological factors which have been recognized recently are the small ionized molecules of the air and the so-called "sferics" which stem from natural electric discharges. It has been claimed that positive space charges have deleterious effects whereas negative space charges have beneficial effects-as illustrated, for example, by enhancement of proliferation of tissue cells exposed in vitro to negative ions.3" Even human patients have apparently benefitted from such treatment. 3 If these claims can be validated, they point to a neglected aspect of biophysics, namely the space charges of small ions.
Air pollution is a bioclimatological factor of increasing importance in the causation of disease. Air pollutants range in kind from pollens and other allergens to toxic gases and aerosols produced by industrial plants, automobile exhausts, and domestic fires. Free HC1 and H2SO4, sulfur dioxide, nitrogen dioxide, ozone, hydrocarbons, and pulverized rubber from automobile tires are but a few of the air pollutants known to exert toxic effects on human, animal, plant, and microbial life.32' 3 The disappearance of lichens from modern cities, and the tremendous toll exacted by chronic bronchitis in certain industrial areas, serve to illustrate the varied aspects and the magnitude of the problem. Ozone deserves to be singled out in this discussion because it is present in large concentration in the smogs over Los Angeles, Phoenix, and Tucson, as well as in the atmosphere reached by high altitude flying. Even short exposure to the concentrations of ozone encountered in these circumstances produces pulmonary oedema and increases the susceptibility of experimental animals to bacterial infections.3436 It is worth mentioning in this respect that in Switzerland the Fohn seems to bring down large amounts of ozone from the upper atmosphere, a peculiarity which has been claimed to account for some of the untoward physiological effects of this type of air current.3