180 Scientific Proceedings, Royal Dublin Society. 



insensitive through, a lack of oxygen. As in the case of the 

 seedlings, the Volvox colonies were screened from the action of 

 light other than that emanating from the radium-tube. The 

 test-tube containing the colonies was supported horizontally during 

 the experiment. 



After twenty-four hours the distribution of the Volvox 

 colonies was observed ; but no - special arrangement due to the 

 action of the radiations was perceptible. Most of the colonies 

 had sunk on to the lower side of the test-tube, but were neither 

 aggregated under the radium-tube nor repelled from it ; while the 

 numerous colonies which still remained swimming freely about 

 showed complete indifference as to their proximity to or their 

 remoteness from the radium-tube. These free-swimming colonies 

 were evenly distributed throughout the body of the liquid and 

 over the walls of the test-tube, and some even were in contact with 

 the glass of the radium-tube. 



These experiments apparently indicate that the radiations 

 from the radium bromide were not able markedly to interfere 

 with the metabolism of the cells experimented with ; nor did they 

 evoke any perceptible response by acting as a stimulus on the 

 protoplasm of light-sensitive cells. It is, of course, possible that 

 by using larger quantities of radium bromide more marked results 

 might be obtained. 



Our joint experiments have up to the present been carried out 

 on four species of bacteria, viz., Bacillus pyocyaneus, B. prodigiosus, 

 B. typhosus, and B. anthracis. They confirm, on the whole, the 

 observations of other investigators. 



In our experiments the bacteria were grown in agar culture- 

 medium, supported on glass or mica plates. The bacteria were 

 either smeared on its surface or diffused through it as an 

 emulsion. 



We found in each case that bacteria exposed to the radiations, 

 and at no great distance from the tube, were inhibited in their 

 development, and in some cases were perhaps killed. 



A few preliminary experiments showed that inhibition of 

 growth only occurred when the bacteria were within about 

 15 mm. of the radium bromide, and that the inhibitory radiations 

 were stopped by a film of agar spread on a glass plate. We 



