A STUDY OF THE EFFECT OF MEASURED DOSES OF ULTRAVIOLET RADIATION ON THE IRRITABILITY OF MELANOPHORES

Abstract

Scales of Fundulus heteroclitus were immersed in various salt solutions and the rate of contraction of melanophores in response to electrical stimulation was used as a measure of their irritability. A Cooper-Hewitt arc was used for the radiation at 5 in. from the scale. No definite knowledge as to the mechanism of contraction was obtained, but Spaeth''s hypothesis that it is similar to the contraction of smooth muscle was supported. The absence of any isoelectric point in the response of the melanophores to ultra-violet radiation in solutions of different ph, makes it unlikely that the contraction is due to a reversible colloidal aggregation. Very satisfactory evidence has been found to show that a small amount of ultra-violet radiation produces an increase in irritability, but that larger doses decrease irritability and eventually cause death. A dose of 1.5 lithopone units gives the maximum increase in irritability. All doses up to 4 units increase irritability. Doses greater than this result in loss of irritability; 27.5 units are lethal. The energy of ultra-violet radiation that causes a maximum increase in irritability in an isolated pigment cell has been measured and is the same whether the radiation is used alone or in combination with visible and infra-red light. Experiments show that increase in irritability is not due to an increase in permeability. Only short radiations with ultra-violet light are stimulating to isolated cells, and longer radiation, even though sub-lethal, produces a depressing effect. Accurate dosage is therefore extremely important in ultra-violet therapy.