350 MICRO-ORGANISMS IN WATER 



prepared from the insolated cover-glass. On the third 

 day the following figures were obtained : — 



Cover-glass exposed 10 minutes to the sun, 360 colonies 

 „ 20 „ „ 130 „ 



5 5 ^^ J) )) ^ J) 



»' 40 ,, ,, o ,, 



„ 50 „ „ 4 „ 



)) t)U }) ,, ,, 



„ 70 and more „ „ 



Thus the destruction is rapid in the first period of 

 exposure, but the more resistant of the microbes take a 

 considerably longer time to annihilate, illustrating once 

 more the individual peculiarities inherent in members 

 of one and the same cultivation. 



Pansini further states, what was affirmed by Arloing 

 but explained and contradicted by Eoux, that the spores 

 of anthrax are more susceptible to light than the bacilli. 

 He mentions that in bouillon containing anthrax spores 

 and exposed to sunlight he has found from thirty 

 minutes to two hours sufficient to destroy them, whilst 

 bacilli under precisely similar conditions required from 

 one to two and a half hours' exposure before being killed. 

 It should be noted that in Pansini's experiments all 

 question of the culture medium being affected by the 

 insolation is removed, inasmuch as the insolated drops 

 containing the organism (whether spores or bacilli) 

 were subsequently transferred to fresh and unexposed 

 culture material, viz., gelatine, in which their survival or 

 decease was put to the test by plate-cultures. We are 

 of opinion, however, that in this method of testing 

 there may lie a source of serious fallacy, inasmuch as 

 the development of anthrax spores in the gelatine- 

 peptone medium is within our own experience often so 

 greatly retarded as to lead to the belief that the spores 

 are dead unless a very prolonged incubation of the 

 plates is resorted to. This may, perhaps, account for 



