770 Prof. H. E. Armstrong on Low-Temperature Research 



Ultra-violet rays, it is well known, are the cause of sunburn. 

 The effect on the eyes produced by sun-glare and by the powerful 

 illuminants now used so widely is also traceable to these rays ; it 

 is no longer felt when these rays are cut off by means of the 

 colourless glasses now in use, which absorb these rays. 



Sir James Dewar has used the organism Photohacterium phos- 

 phorescens in demonstrating the activity of these rays, as emitted 

 by a mercury lamp, even at the low temperature of liquid air 

 (-185°). 



The effect is to kill the bacteria rapidly, even when the culture 

 medium in which they are present is cooled down to - 185°. To 

 quote from the abstract : — 



" Five minutes' exposure, at a distance of a few inches from the 

 mercury lamp, is usually sufficient to kill the bacteria when they are 

 located on the surface layer of the culture medium. The exposed 

 culture is taken out and allowed to warm up in the air. No bright- 

 ness supervenes even after the culture is kept for several hours." 



Other (non-phosphorescent) organisms are equally affected by 

 the rays. 



The death of the phosphorescent organism is also brought about 

 by a number of metals— zinc, copper, silver and especially mercury — 

 when these are introduced into the culture medium. The luminous 

 effect, it may be mentioned, is dependent on the presence of oxygen. 



In referring to this subject, in my previous essay, I remarked, 

 ^' it is clear that the luminosity of phosphorescent organisms is due 

 to a vital process, as the effect is no longer noticeable after disinte- 

 grating the organisms at the temperature of liquid air." It may 

 1)6 pointed out that this passage should not be read too widely. 

 Whilst it is to be supposed that the phosphorescing substance is a 

 product of vital activity,'it isnotto be assumed that the phenomenon 

 itself is dependent upon any " vital " process other than that involved 

 in the production of the material. During my voyage to Australia 

 in the summer of 1914, I made such experiments as I could with the 

 luminous organisms in sea water. When these were collected in a 

 flat dish and observed in the dark, flashes were rarely seen so long as 

 the liquid was still ; but on agitating the contents of the dish, luminous 

 streaks frequently crossed the field, either because the organisms 

 received some mechanical stimulus or because they were brought 

 into contact with oxygen. 



I found that on adding a little toluene or chloroform to the sea 

 water, the flashing took place spontaneously and regularly, even in 

 the still liquid, long after the organisms had been killed by the 

 treatment. 



When in Ceylon later on, I caught a number of fireflies and shut 

 them up in a tube with a few drops of toulene, by which they were 



