EFFECTS OF RADIATION ON BACTERIA 



1133 



11 prodi'ghsus 

 lY Sfaph-pyogen. aur. 



lei experiments were carried out with lethal intensities by way of 

 comparison. 



The problem of the absorption spectra of bacteria is obviously related 

 also to the problem of the possible bactericidal effect of wave-lengths of 

 light in the longer ultra-violet and in the visible regions of the spectrum. 

 It is of interest, therefore, to refer to 

 a few of the several papers in which 

 attention has been given to the 

 absorption by specific bacterial cell 

 constituents which might conceivably 

 be important in the bactericidal 

 effects. 



Through the work of Kubowitz 

 and Haas (cf. Warburg) and of Otto 

 Warburg (154), among others, the 

 absorption of the bacterial pigment, 

 cytochrome, and of certain oxygen- 

 carrying ferments has been deter- 

 mined. The cytochrome absorption 

 bands of the acetic bacteria are 

 found in the green, i.e., about 5500 



o 



to 5600 A, while the ferro-carbon 

 dioxide combination of the respiratory 

 ferment has been identified in the 

 same organism in the yellow, at 5930 

 A. This type of study has been _^ 



extended to other bacteria and to Fig. 3.— Sensitivity curve of B. prodi- 



yeasts; likewise, other yellow r)\vr. giosus &nd Staph, aureus: contmnouB lines 



represent 1 to 10 per cent killing, and 



ments have been found m bacteria, broken lines 90 to lOO per cent killing. 



while methemoglobin has been (From Ehrismann and Noethling, 45.) 



assumed to be present in certain organisms — from the absorption bands 

 in the red. 



RELATIVE SENSITIVITY 



Some differences in the sensitivity of various species of bacteria 

 to the lethal effect of light have been consistently reported. The earlier 

 investigations are of but little value, since such factors as the concentra- 

 tion in cells, presence of absorptive substances in the media or among 

 the by-products, were not taken into consideration. Extensive com- 

 parative studies made under conditions excluding the influence of other 

 modifying factors are not available today, although it seems reasonable to 

 assume that differences in the thickness or color of the cell wall, somatic 

 pigmentation, and the presence of other nonprotoplasmic light-absorbing 

 substances might result in differences of resistance of minor magnitude 



