16 



Dr. A. Downes. On the 



[Jan. 14, 



ported to the British Association in 1881 the results which he had 

 obtained in exposing flasks of animal and vegetable infusions to the 

 influence of an Alpine sun. Corresponding flasks shaded from the 

 light became turbid in twenty-four hours, " while thrice this time 

 left the exposed ones without sensible damage to their transparency." 

 He satisfied himself that this was not due to differences of tempe- 

 rature. The amount of insolation was insufficient, however, to per- 

 manently sterilise the cultures after removal to a warm kitchen. 



Confirmatory evidence also, invested with a special value by the 

 author's great experience of saprophytic life, has more recently been 

 adduced by Professor E. Duclaux.* With the usual precautions he 

 introduced into a flat-bottomed Pasteur flask a drop of pure culture 

 of the organism to be studied, and dried it under a desiccator. After 

 the desired period of exposure to the sun, the flask was charged with 

 sterilised nutrient liquid, of a hind specially suitable to the development 

 of the particular organism, and placed at a favourable temperature in 

 an incubator. Corresponding flasks were kept in the dark. 



He finds that the general rule, that the spores of these organisms 

 resist adverse influences better than their vegetative forms, holds 

 good in regard to the effects of light. This accords with our own 

 observations on the insolation of germs in water.f M. Duclaux, how- 

 ever, reserves for a future memoir his conclusions on the insolation of 

 the micrococci — among which the formation of spores is not certainly 

 known. 



The very hardy spores of the Bacillus, to which he has given the 

 name of Tyrothrix filiformis,% were destroyed by thirty-five days' ex- 

 posure to an autumnal sun. T. geniculatus was more resistant, but 

 showed signs of commencing enfeeblement. T. scaber was only 

 retarded in development by insolation during the month of August, 

 1884, but a further exposure to the end of September — a not very 

 fine month — sterilised two flasks out of four. 



Similar spores had survived for three years in the dark. Like 

 Professor Tyndall, he was satisfied that these results were not 

 effects of temperature ; his insolated flasks scarcely reached any point 

 higher than their fellows kept in darkness in an incubator. 



He concluded, also, from further experiments, that the injurious 

 influence of light here manifested was probably an affair of oxida- 

 tion. 



M. Duclaux very rightly insists on the importance of careful adap- 

 tation of the nutrient liquids to the organisms operated upon, ob- 

 serving that, otherwise, spores might be regarded as dead which had 

 only, perhaps, been enfeebled. " C'est la l'objection," he continues, 



* " Ann. de Chim. et de Phys." 6e ser., t. y, Mai, 1885. 

 f " Proc. Roy. Soc," vol. 28, pp. 203-4. 



% " Etudes sur la lait," " Ann. de l'lnstit. Agronomique," 1879-80. 



