158 DIVERSIONS OF A NATURALIST 



Luminous bacilli or bacteria only give out light when 

 free oxygen is in the water or liquid inhabited by them. 

 A chemical combination of the oxygen with substances 

 in the bacteria is the necessary condition of their evolution 

 of light. When frozen, these bacteria cease to be lumi- 

 nous — the chemical combination cannot take place when 

 the substance of the bacterium is frozen solid and main- 

 tained in that condition ; the liquid condition is a 

 necessary condition for these changes. These luminous 

 bacteria have been used recently by Sir James Dewar in 

 the Faraday Laboratory of the Royal Institution (where 

 Sir James has shown them to me), for the purpose of 

 investigating the action of intense cold on living matter. 

 Although their luminous response to oxygen is arrested 

 when they are frozen, yet immediately on allowing the 

 temperature to rise above freezing-point the response of 

 the living matter to oxidation recommences, and a 

 luminous glow is seen. Hence we have in this glow a 

 ready means of answering the question, " Does extreme 

 cold, of long duration, destroy the simplest living matter?" 

 Sir James Dewar has exposed a film of these bacteria to 

 the extremest degree of cold as yet obtained in the 

 laboratory, that at which hydrogen gas is solidified, and 

 he has kept them in this, or nearly this, degree of cold 

 for several months. Yet immediately on "thawing" the 

 luminous glow was visible in the dark, showing that the 

 bacteria were still alive. Curiously enough, whilst all 

 chemical action in living matter can be thus arrested by 

 extreme cold, and yet resumed on rise of temperature 

 and restoration to the liquid condition, so that the old 

 phrase and the conception of " suspended animation " are 

 justified — yet there is one widely-distributed form of 

 activity, the effect of which the bacteria, even when 

 hard frozen, cannot resist, namely, that of the blue 

 and ultra-blue rays of light. These rays, if allowed to 



