QUANTUM RELATIONS IN PHOTOREACTIVATION OF COLPIDIUM

1. The amount of visible or long ultraviolet light (UV) required to photoreactivate Colpidium colpoda injured with known dosages of short UV (2654 A) was determined. 2. The effect of the short UV was tested by the delay in division of exposed animals compared to controls. Photoreactivation was tested by the effect of postillumination on the delay of division of treated colpidia compared to controls. 3. Colpidia were used in two physiological states: well fed and starved in balanced medium for 48 hours. The latter are much more sensitive to short UV although less susceptible of photoreactivation. 4. Photoreactivation occurred over the entire span from 3350 A to 4350 A for the well fed colpidia, from 3130 A to 5490 (green) for starved colpidia. 5. The photoreactivating effect of a single quantum of blue (4350 A) or long UV (3660 A) delivered per quantum of 2654 A used to injure colpidia was too slight to be considered significant. The effect of 10 quanta was usually more pronounced, but only after 100 quanta had been delivered was the photoreactivation nearly maximal for well fed colpidia. 6. The quantum requirement for maximal photoreactivation of the starved animals was greater at all wave lengths tried: 3660, 4050, 4350, and 5460 A being of the order of 800 incident quanta per incident quantum of 2654 A. 7. The transmission of UV(2654 A), blue, yellow, and red light by a suspension of colpidia was determined. 8. Large dosages of blue, violet, or long UV were slightly injurious to starved colpidia. In a few cases large dosages of 3660 A killed starved colpidia, especially after a non-lethal dose of short UV(2654 A). 9. Photoreactivation seems to be a balance between the slight injurious effect produced by the visible light or UV of long wave lengths and the injury produced by short wave length UV. 10. Possible reasons for the large number of quanta of photoreactivating light required per quantum of short UV are discussed.

The production of new radiations by light scattering. —Part I

In two preliminary papers we have recorded the discovery that when monochromatic light is scattered in a transparent medium (be it gas, vapour, liquid, amorphous solid or crystal), the diffused radiation ceases to be monochromatic, and several new lines or sometimes bands (associated in many cases with a continuous spectrum) appear in the spectrograms of the diffused radiation. Further, the new radiations are, in general, strongly polarised. That the phenomenon is entirely distinct from what is usually known as fluorescence is clear from the fact that the effect is observed when both the exciting radiation and the new radiations generated by it are far removed from the characteristic ultra-violet and infra-red frequencies of the medium. As an illustration we may mention the case of transparent crystalline quartz in which the effect is very well shown with the 4358 A. U. line of mercury as the exciting line, the new lines also appearing in the indigo-blue region of the spectrum. Our preliminary studies have proved conclusively that the effect arises in the following way: The incident quantum of radiation is either scattered as a whole, in which case we have the classical scattering, or else is absorbed in part by the molecules of the medium, the remaining part appearing as a scattered quantum. The part absorbed shifts the molecule to a level of energy different from the initial state. The possibility of a process of this kind, in respect of the electronic state of an atom, was first contemplated by Smekal, and figures prominently in the theory of dispersion due to Kramers and Heisenberg, and in the papers of Schrödinger. Our experiments furnish definite proof of the possibility of such processes, and show that they may occur also in such complicated systems as the molecules of a vapour or a liquid or even in a complete crystal. In the series of papers of which this is the first our further studies of the new radiations will be discussed.