338 MICRO-ORaANISMS IN WATER 



perature from rising beyond 40° C. These cocci forms 

 were introduced into neutralised veal-broth, and it was 

 found that when preserved from the action of light, 

 or exposed onlj to diflfused light, they remained alive 

 at least a year. An exposure to the sun in the spring 

 and early summer (May 4 to June 13) could not be 

 borne by them for longer than forty days, whilst in 

 July fifteen days' insolation was sufficient for their 

 destruction. The cocci of ' Clou de Biskra ' and ' Pem- 

 phigns,' after being preserved in a dried condition in 

 the dark for five or six months, succumbed after eight, 

 three, and even two days' insolation in July. The 

 micrococci, therefore, were much more rapidly destroyed 

 by light than bacilli, and they were also found to be 

 less refractory in a dry than in a moist state. According 

 to Duclaux, therefore, the temperature has nothing to 

 ■do with the action of light. Almost simultaneously 

 with these experiments by Duclaux, Arloing^ examined 

 the efiect of light on the anthrax bacillus, and this is 

 the first instance of a pathogenic bacillar form being 

 ■selected for investigation. The culture medium em- 

 ployed was chicken-broth, and the experiments were 

 carried out in a dark room, a large gas-lamp being 

 the only source of illumination. Test-tubes containing 

 sterile broth were inoculated either with the spores or 

 bacilli of anthrax, and placed in an incubator. The 

 latter was divided into two chambers, the one being 

 dark, whilst the other was, lined with white paper, and 

 admitted light from the powerful gas-burner in question. 

 It was found that the anthrax bacilli flourished equally 

 well whether preserved in the dark or exposed to 

 diffused gas light, but that when exposed to gas-light 



^ * Influence de la Lumi^re sur la Vegetation et les Propri^t^s patho- 

 genes du Bacillus] Anthracis,' Comj)t. rendus hebd, des Stances de 

 VAcademie des Sciences, 9 Fev., 1885, tome c, p. 378. 



