ON BACTERIOLOGY IN ITS RELATIONS TO CHEMICAL SCIENCE. 461 



is due to the presence of some ingredient or ingredients in the urine, and 

 that it is not 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 peroxide of hydrogen in the liquid. Now, 

 as I have already pointed out in connection with my own experiments, a 

 number of investigators are agreed that bacteria are much more resistant 

 to insolation when suspended in water than when suspended in culture 

 matea-ials. It is, however, equally certain that they are actually de- 

 stroyed, and sometimes even with great rapidity, when suspended in 

 water. Now this at first sight would appear to demonstrate that the 

 bactericidal effect of light, although accelei'ated by the generation of 

 peroxide of hydrogen, may also take place without it. But we have 

 already admitted the possibility of the generation of peroxide of hydrogen 

 within the cells of imperfectly dried bacteria and their spores, so that 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 evidence so far would appear to indicate, therefore, that, whilst 

 the genei'ation of peroxide of hydrogen is undoubtedly in many cases an 

 active factor in the bactericidal influence of light, it is still uncertain 

 whether it is indispensable for the process. 



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- va^iour — and 

 the evidence on this larger question goes entirely to show that all 

 apparently direct low-temperature oxidations require the presence of 

 water vapour. And, inasmuch as the bactericidal action of light ia 

 unquestionably a case of low-temperature oxidation there is the strongest 

 presumptive evidence, as well as weighty experimental evidence, that 

 water vapour, which practically means peroxide of hydrogen or some 

 similar material, is essential for its manifestation. 



One of the most important circumstances, from a practical point of 

 view, connected with this bactericidal action of light is the greatly 

 increased resistance which is exhibited by bacteria when suspended in 

 water. On this subject I have for some time past been conducting some 

 experiments, and although these are not yet by any means concluded, I 

 may take this opportunity of referring to some of the results at which I 

 have arrived. In the first place, I would point out how fallacious must 

 be any comparison between the length of insolation withstood by even 

 one and the same micro-organism in the hands of different observers, as 

 so much depends upon their previous history and treatment. Thus I 

 have found that the spores of anthrax produced at the ordinary room 

 temperature (18-20° C.) are far more resistant than anthrax spores 

 which have been obtained in an incubator at 35-38° C. It is necessary, 

 therefore, in all such investigations, if comparisons are to be made,, 

 that the organisms should be taken from one and the same cultivation. 

 In endeavouring to ascertain the greater susceptibility of bacteria to light 

 when exposed in culture media I am proceeding by way of synthesis, 

 making various additions to distilled water, and then determining how 

 such additions affect the influence of insolation. In this manner I have- 

 already made some preliminary experiments with common salt and' 

 sodium sulphate. 



The results of one series of these experiments are recorded in the- 

 following table : — 



