708 VERHOEFF AND BELL. 



known clinically that snow lilindness has often been reported in polar 

 exploration. In high latitudes at sea level the abiotic energy is greatly 

 reduced but three circumstances enter the case to increase the danger 

 of snow blindness. First the hours of sunlight are very long, second, 

 intense cold is believed to decrease the atmospheric absorption for 

 the extreme ultra violet, and third, the exposure of the eye to 

 prolonged and intense cold, while it may not actually lower the 

 vitality of the cells to render them more easily attacked by abiotic 

 radiation, unquestionably would tend to lower their recuperative power 

 and so effect the summation of exposures which ordinarily would be 

 relieved by continuous repair. 



Solar Erythema. 



These data on solar energy at once call up the question of solar 

 erythema generally attributed to the effect of ultra violet radiation.* 

 Clinically this bears a suggestive resemblance to photophthalmia in 

 that it has a period of latency and a similar period of duration. 

 Further it is well known to occur easily at high altitudes with the sun 

 running high, that is under circumstances which afford a fair amount 

 of abiotic rays. The best recent investigation of this matter is that 

 by Dr. deLaroquette,^^° Surgeon Major of the French Army in 

 Algiers. His experiments under the intense tropical sun show the 

 connection of solar erythema with the abiotic rays very clearly. In 

 the first place in most cases he noted a primary erythema clearly 

 due to temperature and perhaps associated with heated air as well as 

 radiation, occurring only when the temperature is 30 degrees C. or 

 more. This is followed after a period of latency of an hour or two 

 by a secondary photochemical erythema going on under severe expo- 

 sures to hemorrhagic pigmentation, local oedema and subsequent 

 desquamation. Experiments in exposure of the skin under screens 

 showed under layers of quartz and water, both of which are highly 

 transparent to abiotic rays, the secondary erythema was well marked. 



* It may be mentioned here that there are certain rare chronic affections of 

 the skin, notably xeroderma pigmentosa, that are believed to be due to exposure 

 to day light, chiefly because they involve only the exposed surfaces of the 

 body. It is supposed that for some unknown reason the skin is in such cases 

 abnormally sensitive to, abiotic radiations. Possibly other slight irritants 

 applied for the same length of time would produce similar effects. Two cases 

 have been recorded in which the cornea was involved, and one of us has per- 

 sonally examined such a case. 



