380 



Dr. A. B. Green. 



[Apr. 11, 



of this ; while by far the greatest resistance was shown by spores, 

 these not being killed by less than 72 honrs' exposure. 



Experiments have also been made from which the following points 

 have been noted. 



1. As the distance between the radium and the micro-organisms 

 subjected to its emanations was increased, the germicidal action which 

 was marked at the nearest distance became less evident and finally 

 ceased to be exerted. 



In these experiments Staphylococcus pyogenes aureus was used, a 

 separate strain being used for each series of experiments. Portions of 

 growth were subjected to the radium emanations for the same time and 

 under the same conditions, except that the distance between the radium 

 and the bacteria was varied. After 30 hours' exposure it was found 

 that — 



At 1 mm. bacteria were killed. 



At 1 cm. bacteria were usually lessened in numbers, but all were not 

 killed. 



At 10 cm. no definite germicidal action was apparent. 

 The following is an example : — 



Experiment. Staphylococcus pyogenes aureus exposed to radium emana- 

 tions for 30 hours at different distances. 



Series. 



Number of bacteria 

 originally present per 

 platinum loopful of 

 emulsion. 



Number of bacteria present per 

 platinum loopful of emulsion after 

 30 hours' exposure to radium. 



At 1 mm. 



At 1 cm. 



At 10 cm. 







1 (*) 



1 («) 



1060 

 1700 

 1200 







160 



987 



2. As extra thicknesses of mica or glass were interposed between the 

 radium and the micro-organisms exposed to their influence, the time of 

 germicidal action was delayed. Finely woven copper gauze also caused 

 slight delay of germicidal action. A sheet of lead 0*1 mm. thick, 

 placed between the radium and the micro-organisms, caused weakening 

 of germicidal action, and as extra thicknesses of lead were interposed 

 and the /3-rays were cut off, germicidal action became less and less 

 evident. 



II. — Induced Radio- Activity of Bacteria. 



It has been found that after exposure at a distance of 1 mm. to the 

 radium emanations for 24 — 120 hours, micro-organisms themselves may 



