162 INFLUENCE OF PHYSICAL AGENTS. 
In the writer’s experiments on the cholera spirillum (1892) test 
tubes, containing sterile bouillon inoculated with one or two ése of a 
pure culture, were sterilized by two hours’ exposure to direct sunlight 
(in December). 
Dieudonné (1894) found that the electric are light destroyed his 
test organisms (Bacillus prodigiosus and Bacillus fluorescens putidus) 
ineight 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 Laquerriére, 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 
fifty milliampéres passed for a quarter of an hour did not kill Staphy- 
lococcus pyogenes aureus, but a current of sixty milliampéres 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 asthe 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 
