1118 
first remains constant; increasing 3, and f makes the 
removal of heat possible. In addition to the “dry” 
climatic factors, e. becomes ever more important. With 
even higher values of 3 and éq, f finally reaches unity, 
and (3% — #,) becomes too small to produce a sufficient 
“radiator effect.’? To remove a constant Q through the 
skin, a peripheral blood flow proportional to 1/(@® — 
8;) is necessary. This value becomes unbearably high. 
In addition, the increased blood temperature and work 
done in internal circulation raise Q [83] (see Fig. 1). 
Cold restricts the peripheral blood circulation and 
thereby decreases ?; and thus also H;. By physiological 
regulation the decrease in skin temperature finally 
causes an increase in Q, varying considerably from 
individual to individual, as a consequence of shivering, 
conscious muscular activity, or thermally excited, 
purely physiological control (Fig. 1). 
In spite of these effects, the core temperature re- 
mains constant in tropical as well as in arctic climates 
(except for extremes) after a brief adaptation period. 
The most important climatic elements in the tropics 
are humidity and temperature; in the Arctic, temper- 
ature and wind. In each case they are modified favor- 
ably or unfavorably by solar radiation. Exercise in- 
creases Q and thus makes warm climates less bearable 
and cold climates more bearable. 
In a cool and moderate climate, variation in pe- 
ripheral blood circulation and the stimulation to in- 
creased heat and food metabolism represent beneficial 
stimuli for healthy people, but a considerable strain 
for those with circulatory diseases. Metabolic and car- 
diovascular diseases as well as mental exhaustion or 
instability, chronic respiratory diseases and rheumatic 
afflictions occur frequently in the area of maximal 
stimulation, for instance, west of the Great Lakes 
[51, 56]. In these same areas we also find the earliest 
onset of growth and sexual maturity in adolescents. 
_ In the warm, humid Tropics, a small amount of 
human activity accompanies a low Q. This condition 
is further augmented by the absence of diurnal, inter- 
diurnal, and annual fluctuations of weather elements. 
The uniformly high values of temperature and humidity 
of the skin decrease its resistance to diseases. This 
decreased resistance, together with the abundance of 
microorganisms and a low social standard, increases 
the number of skin diseases; there are in addition in- 
numerable internal tropical diseases. These illnesses 
might have influenced previous tropical cultures more 
than the climate proper could have done. . 
The dry, hot climates and the tropical highlands 
assume a position between the two extremes noted 
above, since they show a high variability of the weather, 
although at times the heat stress is great. The number 
of microorganisms is small. The dryness of the air is 
favorable to the cure of tuberculosis of the lungs. 
Cultures in these areas (Egypt, Near East, Inca) 
are outstanding and old. 
Survival and culture in the Arctic seem to be a 
matter of providing only food, shelter, clothing, etc. 
Medical geography and climatology [51, 56, 57] may 
have to be rewritten in the next few decades because a 
BIOLOGICAL AND CHEMICAL METEOROLOGY 
large number of the indirect effects of climate, especially 
the infectious diseases (malaria, sleeping sickness, food 
poisoning) can be eliminated. New means of trans- 
portation and storage will eliminate unbalanced diets; 
air conditioning can alleviate peaks of heat stress. The 
sociological situation can thus be changed. The Pygmy 
in the primeval forests of the Congo, the Bedouin in 
the Sahara, and the Eskimo in the Arctic are influenced 
not only by climate, but also by such factors as se- 
clusion and the poverty of the country. 
RADIATION 
The caloric effect of solar radiation was discussed 
above in connection with the over-all heat metabolism 
of the human body. The heat radiation from the clear 
sky is slight. The differences in spectral composition 
between direct solar radiation and sky radiation, each 
considered for various solar elevations, cloudiness, and 
turbidity, are of little importance for the caloric effect. 
On the other hand, a number of photochemical proc- 
esses are connected with shorter wave lengths and are 
thus highly variable with regard to weather. The most 
important of these processes are vision by means of the 
spectrally selective, sensitive retina and the formation 
of erythema, pigment, and vitamin D im the skin 
(for a summary see [12, 16, 69]). 
For measurements in the biologically important range 
below 0.32 » one uses, in addition to spectrographs, 
special instruments such as the cadmium cell of which 
C. Dorno made excellent use, the special photocell of 
Coblentz [26], and the UV-Dosimeter of IG-Farben 
[37] Gor a summary see [60, 69]). Measurements of the 
ultraviolet sky radiation are indispensable in all bio- 
logical investigations since more than half the total 
incoming ultraviolet radiation is scattered by the sky. 
Erythema solare, erroneously referred to as sunburn, 
is produced by the direct action of ultraviolet radiation 
below 0.32 » upon the cells of the skin, perhaps directly 
on the nucleic acid of the cell nuclei (Fig. 2). In this 
process the photochemical sensitivity curve is modified 
by absorption in the uppermost layers of the skin. 
The primary cell damage is followed after about one- 
half hour by reddening of the skin, subsequent swell- 
ing, and in the case of excessive doses, by the formation 
of blisters and epidermic defects after several days. 
In the case of skin with a certain predisposition, the 
same cell damage causes the formation of “delayed 
pigment.’”? This occurs after two to three days and 
consists of a migration of melanin particles to the 
surface. By a different photochemical process, the “im- 
mediate pigment” is formed even more rapidly than the 
erythema. This process is caused by long-wave ultra- 
violet radiation (Fig. 2). It consists of a darkening of 
already present melanins [12, 48, 44, 46]. 
In the case of erythema and of both kinds of pigment, 
one can measure the threshold and also the degree of 
discoloration; the latter is determined by the difference 
in reflectivity at a wave length typical for the particular 
discoloration (green in the case of erythema) [16]. 
The threshold dose required for erythema is essentially 
a value depending on the individual. The threshold 
