354 MICRO-ORGANISMS IN WATER 



prolonged, the bacilli are completely destroyed, whilst 

 they are unaffected if subjected during the same length 

 of time to the red rays only. 



In Santori's^ experiments special attention is be- 

 stowed upon the part played by temperature during 

 insolation. This investigator found (1) that the bacteri- 

 cidal action of light came into play even when un- 

 accompanied by a high temperature ; (2) that the red 

 and violet rays of the spectrum have no specifically 

 different action on bacteria ; (3) that microbes are more 

 refractory as regards light in the dry than in the moist 

 state ; (4) that no appreciable difference was noted in 

 the relative powers of resistance possessed by the spores 

 and bacilli of anthrax respectively ; (5) that the action 

 of the sun and of the electric light was greater accord- 

 ing as the accompanying temperature was higher; 

 (6) that the action of the electric light (900-candle 

 power at a distance of 80 cm.) was distinctly weaker 

 than that of the sun ; and (7) that the virulence of the 

 anthrax bacillus may be diminished through insolation, 

 and be made to serve as vaccine. 



Koch ^ states that the tubercle bacilli (see Appendix, 

 p. 422) were destroyed in direct sunshine in from a few 

 minutes to some hours, according to the thickness of 

 the material in which they were suspended and exposed. 

 Cultures of the tubercle bacillus were destroyed, even 

 in diffused light, when placed close to the window, in 

 from 5 to 7 days. 



We now come to the researches of Eussian inves- 

 tigators. Janowski^ confined his observations to the 



^ Bollettino delV Accademia "inedica di Boma, vol. xvi., 1889-90. 



* ' Ueber bacteriologische Eorschung : ' Vortrag in der ersten aUgem. 

 Sitzung des x. internationalen medicinisclaen Congresses, 1890, quoted by 

 Kitasato, Zeitschrift filr Hygiene^ vol. x. 1891, p. 285. 



^ * Zur Biologie der Typhtisbacillen,' Centralhlatt filr Bakt&riologie 

 vol. viii. 1890, pp 167, 193, 230, 262. 



