Investigations conducted during the last three years have shown that light of definite wave-lengths has specific effects upon the growth of organisms, e.g., yeast, paramecium and tomato rot (Colletotrichum).The organism, Paramecium caudatum, was irradiated in a quartz cell at room temperature with a Cooper-Hewitt "Lab-arc" for periods of 6 and 24 hr. and the rate of plasmolysis in sodium chloride and sucrose solutions then determined. The organisms passed through the same series of reactions in both solutions but plasmolysis occurred much more rapidly in sodium chloride than in sucrose solutions, even when the latter were of greater concentration.It would seem that the effect of light is to increase the rate of plasmolysis under all circumstances, although Packard (8) states that the permeability of the cell membrane is increased with increase of division rate in paramecium.In general there is a marked similarity between the curves showing the increase in rate of plasmolysis and those showing the effect of irradiation on the growth rate of paramecium.In most cases visible and near ultra-violet light caused an increase in the rate of plasmolysis of less magnitude than that caused by the far ultra-violet. All visible and near ultra-violet lines used, with the exception of 4960 Å, 4078 Å and 3022 Å, caused stimulation of division rate and these lines had the least effect on the rate of plasmolysis.The single green spectral line (λ = 4960 Å) had a retarding effect on growth and also caused a decided increase in plasmolysis. The lines 4078 Å and 3022 Å both caused slight decrease in division rate and slight increase in rate of plasmolysis.It would appear that, with few exceptions, the effect of monochromatic lines of the spectrum in increasing the rate of plasmolysis is greater the shorter the wave-length.It has been found that in many cases injury to an organism produces rapid increase and stimulation of growth.From the results of these experiments it would seem that when light energy is absorbed, the physiological condition of the plasma membrane changes. Apparently the conditions accompanying moderate increase in rate of plasmolysis also accompany increase in the rate of cell division in paramecium, and the conditions accompanying excessive increase in rate of plasmolysis result in decrease of growth.

Paramoecium was irradiated with monochromatic light and it was found that rays of different frequencies have specific effects upon its growth. Certain frequencies in the red, the yellow and the near ultra-violet parts of the spectrum were found to stimulate growth; some as in the green and in the far ultraviolet beyond 3000Å retarded it, and even killed the organism at a very low intensity. Other frequencies retarded or stimulated growth during early exposure and later produced the reverse effects.

The effects of radiant energy as procured from a mercury arc, using full irradiation of varying intensity and using also individual wave-lengths transmitted by a monochromatic illuminator, have been determined. The enzymes investigated are the diastases (amylases) of saliva and of malt and the production, first of erythrodextrin and second, of maltose from starch, is used as an indicator of the enzyme activity. These two phases are designated the dextrinogenic and the saccharogenic. Full irradiation retards the dextrinogenic and the saccharogenic activity of both salivary and malt diastase in an inverse relation to intensity. In the case of salivary diastase the rates of dextrin production and of maltose production are decreased by the green and the far ultraviolet wave-lengths, while both tend toward stimulation when irradiated with the red yellow and near ultra-violet wave-lengths. The monochromatic effects on malt diastase are generally inhibitory for the dextrinogenic phase and stimulatory for the saccharogenic phase. These results may be explained by the presence of two enzymes constituting the diastase, one dextrinogenic, the other saccharogenic; either may be the less active and so become the "pace setter" for maltose production; in the dextrinogenic phase one only is considered, in the saccharogenic phase, both are involved; in salivary diastase the dextrinogenic enzyme is the "pace setter", while in malt diastase the saccharogenic enzyme is usually the "pace setter"; full illumination, however, retards the dextrinogenic enzyme until it becomes the "pace setter". The effects of monochromatic light on the growth of paramecium parallel the effects on the activity of salivary diastase and the effects of monochromatic light on the sporulation of Colletotrichum parallel the effects on the saccharogenic activity of malt diastase.