ACTION OF LIGHT ON MICRO-ORGANISMS 369 



dium has been so interfered with during insolation that 

 it no longer affords a suitable nourishing material for 

 the micro-organisms therein which may yet be in a 

 living condition. It will be obvious, therefore, that these 

 experiments of Momont's have distinctly advanced our 

 knowledge of this complicated subject in many direc- 

 tions ; and the confirmation of the fact suggested by 

 previous observers that the nature of the culture 

 medium in which the organisms are contained is of 

 importance is very strikingly worked out for bouillon 

 and blood respectively. 



It will also be noted that Momont does not con- 

 firm Arloing's observations that the spores of anthrax 

 .are more susceptible to light than the bacillar form, for 

 he finds that, whilst the dried spores will withstand direct 

 sunlight for over 100 hours either in the presence or absence 

 of air, the dried bacillar forms succumb after eight hours' 

 insolation in the presence of air and eleven hours in the 

 absence of air when the bacilli were dried in blood, and 

 jive and a half hours' insolation in the presence of air, 

 and six and a half hoars in the absence of air, when the 

 bacilli were dried in bouillon. In no case also was any 

 permanent attenuation of the virus obtained by insolation. 



Marshall Ward l has more recently exposed the dried 

 .spores of anthrax in Petri dishes with alphabetical 

 screens as employed by Buchner (see p. 361), the spores 

 being spread on the glass surface in the absence of all 

 food materials ; after insolation a slab of solidified agar- 

 agar was placed on the film of spores and the whole 

 incubated, with the result that only the spores which 

 had been protected by the screen germinated in the 

 agar-agar. On the other hand, in a converse experi- 

 ment, a slab of agar-agar was first insolated and then 

 laid on the film of spores which had not been exposed 



1 Proc. Boy. Soc. vol. liii., 1893, p. 310. 



B B 



