ACTION OF LIGHT ON MICRO-ORGANISMS 359 



posure to light. It will be remembered tliat Eoux 

 stated that such an alteration took place in broth, 

 whilst Pansini, when using gelatine, could trace no 

 such effect, and Janowski stated that he could also find 

 no such change produced in broth. 



Two sterile gelatine tubes were exposed for from 

 two to three hours to direct sunlight side by side with 

 two into which typhoid bacilli had been introduced. 

 Two control tubes were placed in a dark cupboard. 

 The sterile insolated tubes were subsequently inoculated 

 with typhoid bacilli, and were removed with the other 

 tubes to a dark cupboard. The growth was markedly 

 more feeble in the insolated tubes subsequently inocu- 

 lated with typhoid bacilli than in the control tubes 

 kept from the first in the dark cupboard ; it was, how- 

 ever, somewhat better than in those tubes inoculated 

 with the bacilli and insolated for the above period. 

 Geisler is, therefore, of opinion that a distinctly un- 

 favourable effect is produced upon gelatine during 

 insolation, at any rate as far as its fitness for the 

 cultivation of the typhoid bacillus is concerned. 



Kotljar,^ another Eussian investigator, has made 

 some experiments to ascertain which rays of the spec- 

 trum are mostly concerned in the bactericidal action of 

 light. These were, however, not carried out by means 

 of a spectroscope, but by surrounding the test tubes 

 containing the bacteria under observation with different 

 coloured films of ^gelatine. The culture media em- 

 ployed were agar-agar and potatoes. The results 

 obtained as regards the particular organisms (non- 

 pathogenic) investigated were not so striking as in the 

 case of pathogenic varieties studied by other observers. 



^ * Zur Frage iiber den Einfluss des Lichtes auf Bakterien,' Wratsch, 

 1892, Nos. 39 and 40. Gentralhlatt filr Bakteriologie^ vol. xii., 1892, 

 p. 836. 



