1904] On the Action of Radium on Micro-organisms. 381 



show signs of radio-activity. It has not yet been ascertained whether 

 living micro-organisms can exhibit induced radio-activity, but micro- 

 organisms which have been killed by exposure to the radium emanations 

 can do so. 



In these experiments no radio-activity has been found in bacteria not 

 exposed to the action of radium. 



Induced radio-activity of micro-organisms has been shown in the 

 following manner : — A small mass of bacteria, removed from the surface 

 of nutrient medium, after subjection to the radium emanations at a 

 distance of 1 mm., for, as a rule, 72 hours, was removed from the 

 depression of the hollow-ground glass slide in which it had been 

 exposed to the emanations, and was placed between two thin sheets of 

 glass, generally coverslips, which were not themselves radio-active. 

 These sheets of glass, with the small mass of bacteria pressed between 

 them, were next, in a dark room, brought into contact with the film of 

 an Ilford " special rapid " photographic plate. A cotton-wool pad was 

 placed on the glass sheets to keep them in position, and the whole was 

 wrapped up in a light-proof package. Twenty-four hours later the 

 photographic plate was developed and a photograph was obtained of 

 the bacterial mass. An image has been developed after only 1 hour's 

 exposure of a sensitised plate to the radio-active bacteria, and in some 

 instances after a fortnight's exposure. 



Faint images have been thus produced on sensitised plates by 

 S. p. aureus and albus which had been subjected to radium emanations, 

 but, so far, the best photographs have been obtained from bacterial 

 masses containing a number of spores, after their subjection to the 

 emanations for 24 — 120 hours (Plate 11, fig. 1). 



Eadio-active micro-organisms have continued to give off photo-actinic 

 emanations after 3 months have elapsed since their exposure to 

 radium. 



Photographs of masses of micro-organisms, possessing induced radio- 

 activity, have been obtained ( through a double layer of lead foil (Plate 11, 

 fig. 2). A sheet of lead 3 mm. in thickness interposed between a 

 radio-active bacterial mass and the sensitised plate has prevented the 

 passage of photo-actinic emanations from the glass to the plate. These 

 photographs would seem, therefore, to be caused by /3-rays emitted by 

 the micro-organisms. 



My best thanks are due to Mr. Power, Medical Officer of the Local 

 Government Board, for the facilities he has afforded me in the 

 research, and for the kind and valuable advice he has given me 

 concerning it. 



