For the most part, the effects of visible light on protoplasmic viscosity have been studied by botanists. The reason for this is quite obvious; plant protoplasm is apparently much more sensitive to visible light than is the protoplasm of animal cells. In interpreting the results that have been reported, caution is necessary. If an observer finds that the chloroplasts of interest in the phenomenon of photoreactivation, for this occurs not only in bacteria and fungi, but also in protozoa and in sea urchin eggs. In photoreactivation, the changes produced by ultraviolet radiation of wave lengths around 2,500 Å are counteracted at least to some extent by exposure to radiation of longer wave lengths in the range between 3,300 and 4,800 Å. The subject has been reviewed by Dulbecco (1955). He believes that the primary action is on the nucleus and involves changes in nucleic acid. However, as will be shown later, beyond any question ultraviolet radiation produces changes in the cytoplasm as well as those it might cause in the nucleus. And in so far as the cortical protoplasm of ameba is concerned, the changes produced by ultraviolet radiation are exactly the opposite of those produced by visible light. This follows from the work of Heilbrunn and Daugherty (1933) and of Alsup (1942). In the ameba, as will be discussed more fully later, ultraviolet radiation causes a market decrease in the viscosity of the cortical protoplasm.
KeywordsVisible Light Ultraviolet Radiation Mercury Vapor Lamp Protoplasmic Streaming Violet Radiation
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