ACTION OF LIGHT ON MICRO-ORGANISMS 383 



In these experiments Buclmer's method was employed. 

 In all these experiments it will be seen that nutrient 

 culture media were employed for the insolation, and 

 that the spores were destroyed in a much briefer period 

 of time than in my experiments, in which they were 

 insolated in Thames water. This same phenomenon of 

 the spores of anthrax being more resistant to the action 

 of sunshine in water than in ordinary culture materials 

 has also been observed by Straus {' Society de Biologie/ 

 1886, p. 473) and by Momont (^ Ann. de Tlnst. Past.,' 

 1892, p. 21), who both, however, appear to have made 

 use of distilled water only. 



This greatly increased resistance to insolation which 

 is exhibited by bacteria when suspended in water 

 instead of in culture media, is of great importance from 

 a practical point of view. In the first place we would, 

 however, point out how fallacious must be any com- 

 parison 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 it was found 

 by one of us that the spores of anthrax produced at 

 from 18° to 20° C. are far more resistant than anthrax 

 spores obtained at from 35° to 38° C. In all compara- 

 tive experiments, therefore, the organisms should be 

 taken from one and the same cultivation. 



In endeavouring to ascertain the cause of the greater 

 susceptibility of bacteria to light when exposed in cul- 

 ture media, we are 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 we have already made 

 some preliminary experiments with common salt and 



^ British Association Beports, 1893 ; also Centralhlatt fur Bakterio- 

 ie, vol. XV., 1894, p. 111. 



