342 MICRO-ORGANISMS IN WATER 



during their exposure to light, the temperature being 

 thereby kept below 4 C. By the low temperature thus 

 secured Arloing considered that he had effectually 

 banished the possibility of the spores germinating into 

 bacilli, and under these conditions again he was able to 

 demonstrate the complete destruction of the anthrax in 

 five hours. Arloing, however, also found that a longer 

 period of insolation was necessary for the destruction 

 of anthrax spores when the latter were placed in water. 

 A further confirmation of these experimental results, 

 but with an entirely different explanation, was furnished 

 in an exceedingly interesting and suggestive paper by 

 Eoux, to which we shall presently refer. 



Meanwhile some fresh observations of Arloing 

 must be recorded concerning the conditions under 

 which light acts upon bacteria. In one of his memoirs 

 (see note 1, p. 339) already referred to, the observation 

 is made that if an obstacle be placed between the source 

 of light and the object of experiment in the shape of a 

 layer of distilled water a few centimetres thick, the 

 bacteria thus exposed will remain almost as little affected 

 as if they were kept in darkness. This result is con- 

 firmed by a number of experiments made by this inves- 

 tigator, and recorded in another memoir published in 

 the Archives de Physiologie (see note 3, p. 341). Here it 

 is stated that a layer of distilled water two centimetres 

 thick placed between the sun's rays and the experi- 

 mental vessels will almost completely nullify the delete- 

 rious effect of the light, but that not all liquids are 

 possessed of this protecting power, for out of three ex- 

 periments in which a solution of alum was employed in 

 the place of distilled water, in two the spores were 

 destroyed as usual, whilst in the other case their de- 

 velopment was delayed for twenty-four hours. Arloing 

 does not seek to explain these most remarkable results, 



