EFFECT OF EXPOSURE TO THE SUN ON THE CIRCULATING LYMPHOCYTES IN MAN.

Chronic solar dermatitis was accompanied, in 25 of the 38 individuals studied, by an appreciable increase, percentage and absolute, in the number of circulating lymphocytes. In eight there was a definite decrease and in five no appreciable change after prolonged exposure to the rays of the summer sun. Of the thirteen subjects with no increase in blood lymphocytes, six failed to tan, three were so dark originally that to determine an increase was impossible, and five had an extremely high lymphocyte count at the first count. Blood counts on white persons living in the Philippines indicate that the blood lymphocytes are likewise increased after a prolonged period of residence in the tropical zone. Because of the parallelism between the tanning and the blood changes it seems probable that the lymphocytosis observed in the majority of instances, which is similar to the response of the blood of animals to small doses of the x-rays, is due to the effects of the ultra-violet rays contained in the solar spectrum.