PHYSICAL BIOCLIMATOLOGY 
dose D of white persons is 50 < D< 600 (D= ul- 
traviolet intensity in units of the IG-Farben Dosimeter 
x time in minutes) [16, 54]. The mean value of all 
persons examined (mostly blond) was D = 200, a value 
which corresponds to a 15-min exposure to sun and sky 
at 60° solar altitude in middle latitudes. In all persons 
the reddening measured by means of a reflectometer 
increased by about 1 per cent for each 80 D units above 
the threshold value of D. Different climates (arctic to 
tropic), the temperature of skin or air, the origin of 
the radiatien (sun or sky), wind, ete., do not influence 
the relation of D and the erythema produced [16, 64]. 
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PERCENT 
0.5 
WAVE LENGTH (#) 
Fic. 2.—Threshold and absorption spectra for the human 
body. Blood—decrease in light intensity when passing through 
a layer of blood corpuscles 7.8 » thick (about equal to the 
diameter of one blood corpuscle). Skin—loss in passing through 
a light-brown layer of: skin 0.8 mm thick. "erment—breathing 
ferment, according to Warburg, which is held responsible for 
the effect of violet light. Vitamin D—absorption coefficient of 
nonirradiated ergosterin. Hye—sensitivity curve of the normal 
eye, adapted to daylight. The outer limits lie at 800 and 320 
my. Pigment—the curve of direct pigmentation due to long- 
wave ultraviolet, the so-called “immediate pigment,’’ ac- 
cording to Henschke and Schultze [46]. EHrythema—skin-red- 
dening curve plotted according to the reciprocal values of the 
excitation threshold. In the curves ‘‘blood,’”’ ‘“‘skin,’”’ and 
“ferment,” light depletion is represented; 100 denotes opacity. 
In the case of ‘‘vitamin D,’”’ the numbers, which have been 
divided by 100, represent the absorption coefficients. All other 
curves are referred to the maximum of the curve in question. 
(After Pfleiderer and Buettner [69].) 
Immunity against erythema can be attained by the 
“delayed pigment,” by thickening of the epidermis, or 
by both. Ointments which do not transmit at \ < 0.32 u 
afford protection against erythema without preventing 
the formation of “immediate pigment.” A light ery- 
thema may be a desirable stimulus for a healthy person; 
on the other hand, an acute form is associated with a 
dangerous activation of tubercular lung processes and 
may, in rare cases, even cause skin cancer. The cos- 
metic value of the pigment is a matter of fashion. 
Vitamin D, which is indispensable for the formation 
of bones, is produced from the ergosterin of the skin by 
almost the same radiation (Fig. 2) and at about the 
same superficial skin layer as erythema. Since this 
1119 
vitamin nowadays can also be taken orally, rickets can 
no longer be considered a climatic disease. 
The ultraviolet radiation below 0.32 » varies more 
than that of any other part of the solar spectrum. It is 
absorbed by the atmospheric ozone, highly scattered 
by air and aerosol, and reflected by snow. The effect 
of dust above large cities is frequently overestimated ; 
the loss for Boston [41] and Berlin [16] amounts to less 
than 20 per cent for the noontime sun, and even less 
for the sky. In Berlin the loss is no greater for the 
ultraviolet than it is for the other wave lengths. 
Taste IL. UttrRAviouer IntTENsIty or SuN AND Sxy* 
Sun’s elevation 
Region 
10° | 20° | 30° | 40° | 50° | 60° | 70° | 90° 
Northern and central 
Europe, and central 
Africa, altitude 
<< BOO) ONS 5 oad balsa ol 1 3] 6] 8] 11) 14) —}]— 
Oceans in tropical lati- 
CuUdes ea ae erent pes QA a 2A 228 2737, 
Central Europe, altitude 
TSO WM eevee ae ee — |} 4] 8} 12] 16} 20] — | — 
Central Europe and cen- 
tral Africa, altitude 
approx. 3000 mm... 5..../— || 5) 11) 16) 21) 26) |) 31) 42 
* Measured with the IG-Farben UV-Dosimeter, 1938 model, 
during the warm season and with a clear sky (summarized 
in [69]). 
Table II shows measurements made with the IG- 
Farben Dosimeter (1938 model) from Lapland to the 
hills of the Belgian Congo. Table III shows the effect 
of clouds of medium thickness on the ultraviolet radi- 
ation of sun plus sky. 
Taste III. Errecr or CLouUDINESS ON 
ULTRAVIOLET RADIATION* 
Cloudiness %o | 30 | Ho } Sto | S40 | 1%0 
Percentage of ultraviolet radia- 
HON UTS AMM «so noneananes 100 | 90 | 75 | 65 | 55 | 45 
* For clouds of medium thickness, with average elevation 
of sun. 
The brightness and color of the surroundings produce 
a number of psychological and physiological effects via 
the eye. The greatest change in this field, the intro- 
duction of electric illumination at the beginning of this 
century and the resulting elimination of biological dark- 
ness during the winter, is held responsible for the more 
rapid maturing of adolescents observed since that time. 
Glare is typical of two climates: the arctic and the 
subtropic, where bright snow or sand, abundant sun- 
shine (subtropic), and the scarcity of natural shadow 
coincide. Temperate and tropical zones have less sun- 
shine as well as a darker background and numerous 
sources of shadow. Glare increases the contrast thres- 
hold of the eye, impairs space perception, and makes 
landscapes appear flat. Snow blindness may be due to 
glare as well as to an ultraviolet erythema of the eye. 
The beneficial or, in the case of an excess, harmful 
effect of the natural radiation encountered in the open 
