390 MIORO-ORGANISMS IN WATER 



formed by the insolation of water, or even of a solution 

 of urea. If, then, the bacteria are suspended in water 

 during insolation, there can be no generation of per- 

 oxide of hydrogen in the liquid. Now, as I have 

 already pointed out in connection with my own experi- 

 ments (' Proceedings Eoyal Society,' 1893), a number of 

 investigators are agreed that bacteria are much more 

 resistant to insolation when suspended in water than 

 when suspended in culture materials. It is, however, 

 equally certain that they are actually destroyed, and 

 sometimes even with great rapidity, when suspended in 

 water. Now this at first sight would appear to demon- 

 strate that the bactericidal effect of light, although 

 accelerated by the generation of peroxide of hydrogen, 

 may also take place without it. But in the experi- 

 ments which have hitherto been made on the action of 

 light on micro-organisms, those conditions have not 

 been secured which entirely preclude the generation of 

 peroxide of hydrogen within the cells of imperfectly 

 dried bacteria and their spores, and it is highly probable 

 that this generation does take place, and it is surely 

 still more easy to believe in the production of this 

 material within the cells suspended in water to which 

 air has access. The question obviously raises another 

 and far more general question, which has long been 

 before the chemical world, viz., as to how far oxidation 

 can take place at all in the entire absence of water ; 

 and the evidence on this larger question goes entirely 

 to show that all apparently direct low-temperature 

 oxidations require the presence of moisture. And, 

 inasmuch as the bactericidal action of light is unques- 

 tionably a case of low-temperature oxidation, there i& 

 the strongest presumptive evidence, as well as weighty 

 experimental evidence, that moisture, which practically 

 means the possibility of the presence of peroxide of 



