15 8 INFLUENCE OF PHYSICAL AGENTS. 



In the writer's experiments on the cholera spirillum (1892) test 

 tubes, containing sterile bouillon inoculated with one or two ose of a 

 pure culture, were sterilized by two hours' exposure to direct sunlight 

 (in December). 



Dieudonne (1894) found that the electric arc light destroyed his 

 test organisms (Bacillus prodigiosusand Bacillus fluorescens putidus) 

 in eight hours. The same result was accomplished by the incandes- 

 cent light in eleven hours. 



In view of these facts we may conclude, with Duclaux, that sun- 

 light is one of the most potent and one of the cheapest agents for the 

 destruction of pathogenic bacteria, and that its use for this purpose is 

 to be remembered in making practical hygienic recommendations. 

 The popular idea that the exposure of infected articles of clothing 

 and bedding in the sun is a useful sanitary precaution is fully sus- 

 tained by the experimental data relating to the action of heat, desic- 

 cation, and sunlight. 



Electricity. Cohn and Mendelssohn, in 1879, attempted to de- 

 termine the effect of the galvanic current upon bacteria. Cultures 

 were placed in U -tubes through which a constant current was passed. 

 A feeble current was found to be without effect. A strong current 

 from two elements, maintained for twenty-four hours, restrained de- 

 velopment in the vicinity of the positive pole, but this was probably 

 due to the highly acid reaction which the culture liquid acquired. 

 When a current from five elements was used for twenty-four hours 

 the liquid was sterilized, but this may have been due to the decided 

 changes produced in the chemical composition of the culture liquid 

 rather than to the direct action of the galvanic current. 



The same may be said of the similar results obtained in later ex- 

 periments by Apostoli and Laquerriere, and by Prochownick and 

 Spaeth. The last-mentioned investigators found that the positive pole 

 had a more decided effect than the negative, and that the effect de- 

 pended upon the intensity and duration of the current. A current of 

 lit ty milliamperes passed for a quarter of an hour did not kill Staphy- 

 lococcus pyogenes aureus, but a current of sixty milliamperes main- 

 tained for the same time did. The spores of Bacillus anthracis 

 required a current of two hundred to two hundred and thirty milli- 

 amperes during an hour or two. In these experiments the cultures 

 in gelatin were attached to the strips of platinum serving as the two 

 poles, and these were immersed in a solution of sodium chloride. As 

 chlorine was disengaged at the positive pole, the germicidal action is 

 attributed to this gas rather than to the direct action of the current 

 upon the living microorganisms. 



The more recent researches of Spilker and Gottstein, made with 

 an induction current from a dynamo machine, are more valuable in 



