1132 



BIOLOGICAL EFFECTS OF RADIATION 



Curves were obtained characteristic of biological fluids containing protein 

 material. These curves present a general similarity to the reciprocals of 

 the curves for bactericidal effect (Fig. 2). It is not regarded as sig- 

 nificant that there are certain differences in the sets of curves referred to, 

 since, while all the products of the cell will contribute to the total absorp- 

 tion, it is scarcely possible that absorption by all such products will be 

 effective, that is, participate in the bactericidal effects. In general, this 

 study reveals the existence of an absorption maximum between 2600 and 



o 



2700 A, corresponding strikingly to the maximum bactericidal effect. A 



second maximum seems to be 

 approached below 2300 A (Fig. 2). 

 This work has been criticized (45) on 

 the ground that the determinations 

 were made with energy intensities 

 sufficient to cause the death of the 

 bacteria during the interval of ex- 

 posure, so that the absorption curves 

 given would actually represent the 

 absorption by dead bacteria. 



Various students of lethal effects 

 have directed attention to the proba- 

 bility that the energy resulting in 

 killing is absorbed by a comparatively 

 small part of the cell organization, and 

 this is independent of any "specific 

 volume," as often dis- 

 cussed elsewhere in the literature. It 

 would seem to be clear, therefore, 

 that no absorption curve found could approach an accurate picture of a 

 theoretical absorption spectrum of the essential material or materials. 



Ehrismann and Noethling (45) discuss at some length the difficulties 

 and the sources of error in any final determination of absorption values 

 that actually represent effective absorption, that is, absorption by those 

 cell constituents that may lead directly or indirectly to lethal effects. 

 While recognizing the desirability of determining the absorption of those 

 substances only that are sensitive to changes resulting in death, they find 

 no procedure that is entirely satisfactory. Theoretically, the reciprocal 

 of the curve of bactericidal action is perhaps the best absorption curve 

 available. No absolute comparisons were attempted, since the con- 

 centration used for each organism was so adjusted that the measurements 

 with the photocell employed were within the range of the greatest accu- 

 racy (Fig. 3). In general, the procedure employed was calculated to 

 assure work with living cells, since the intensity of the radiation utilized 

 was far below the threshold of bactericidal action. Nevertheless, paral- 



022 Q23 024 Q25 Q26 Q27 Q28 Q?9 030 031 032 

 Wave Length in^ 



Fig. 2. — The coefficients of absorption sensitive 

 of ultra-violet radiation by a layer of B. 

 coli 0.8 n in thickness. {From Gates, 60.) 



