1136 BIOLOGICAL EFFECTS OF RADIATION 



the lethal action of ultra-violet radiation, Minck (103) in 1896 was appar- 

 ently the first to undertake a determination of the efficiency of X-rays as 

 a bactericidal agency. He used a strain of the typhoid bacillus, streaking 

 the surface of agar plates, and exposing certain areas as long as 8 hr., at a 

 distance of 10 cm., to radiation from a Hittorf tube. Following an 

 incubation period, no effect of the irradiation could be detected from the 

 gross appearance of colony development. 



Among others investigating X-ray effects with negative results may 

 be mentioned Beck and Schultz (11). Negative results were also 

 obtained by Wittlin (163) using six species of bacteria exposed in tubes 

 of peptone bouillon, subcultured before and after exposure. In fact, 

 while negative results were being generally reported at this time 

 (1896-1897) indications were accumulating which were interpreted as 

 showing indirect effects of radiation on bacteria; thus animals inoculated 

 with the tubercle bacillus were irradiated and compared with similarly 

 inoculated and unirradiated controls with respect to disease development. 

 In this way some positive indications were furnished. Nevertheless, more 

 consideration in establishing the bactericidal action of these rays should 

 be given to such investigations as those of Rieder (130), in 1898. He 

 used six organisms {B. anthracis, B. coli, B. diphtheriae, the tubercle 

 organism, a streptococcus. Staphylococcus pyogenes aureus, and Vibrio 

 cholerae), exposing these on agar or gelatin media. They were killed 

 after irradiation intervals of 40 to 60 min. at a distance of 10 cm. On the 

 whole, less consistent and satisfactory results were obtained with some 

 of these organisms when exposed in bouillon or in a meat extract medium 

 5 mm. in depth. The general trends of such results were confirmed by the 

 later work of Rieder (130) and others. 



With the intensities which continued to be employed during the next 

 quarter century few significant advances were made; true, exposure 

 periods were considerably extended, but this practice could not be 

 expected to yield satisfactory results under conditions favorable for 

 continued growth and multiplication. Even less satisfactory were the 

 results in which cultures were exposed for an interval on successive days. 

 Results obtained by Russ (134) were important in showing that while the 

 irradiation of inoculated animals might increase their resistance to the 

 disease normally induced, still such intensities as he employed produced 

 no evident effect on the morphology or physiology of the bacteria when 

 irradiation of these organisms was carried out independently. Haber- 

 land and Klein (69a) worked with a spark length of 35 cm. and current 

 2 to 2.5 ma., giving an exposure up to twice that required for 1 H.E.D., 

 with negative effects on a "human" strain of the tubercle bacillus, while 

 Lange and Fraenkel (92) found that a dosage of 10 H.E.D. (2 ma., and 

 spark length 7 to 8 cm.) greatly diminished the infectivity of a culture of 

 this organism 33 days old, as evidenced by inoculation of the organism 



