BIOLOGY OF BACTERIA. 47 



direct rays of the sun, and to a less degree the intense 

 rays of the electric arc-light, retard and in numerous in- 

 stances kill bacteria. Some colors are distinctly inhibi- 

 tory to their growth, blue being especially prejudicial. 

 Some of the chromogenic forms will only produce their 

 colors when exposed to the ordinary light of the room. 

 The Bacillus mycoides roseus will not produce its red 

 pigment except in the absence of light. The pathogenic 

 bacteria have their virulence gradually attenuated if 

 grown in the light. 



(/) Electricity. — Very little is known about the action 

 of electric currents upon bacteria. Very powerful dis- 

 charges of electricity through culture-media are said to 

 kill the organisms, to change the reaction of the culture, 

 and the rapidly reversed currents of high intensity to 

 destroy the pathogenesis of the bacteria and change their 

 toxic products into neutralizing protective (antitoxin ?) 

 bodies. Much attention has recently been devoted to 

 this subject by Smirnow, Arsonval and Charin, Bolton 

 and Pease, Bonome and Viola, and others. 



(g) Movement. — When bacteria are growing in a liquid 

 medium perfect rest seems to be the condition best 

 adapted for their development. A slow-flowing move- 

 ment does not have much inhibitory action, but violent 

 agitation, as by shaking a culture in a machine, greatly 

 hinders or prevents their growth. The practical appli- 

 cation of this will show that rapidly flowing streams, 

 whose currents are interrupted by falls and rapids, will, 

 other things being equal, furnish a better drinking-water 

 than a deep, still-flowing river. 



(//) Association. — It occasionally happens that bacteria 

 grow better when associated with other species, or have 

 their pathogenic powers augmented when grown in com- 

 bination. Coley found the streptococcus toxin more 

 active when combined with Bacillus prodigiosus. 



Occasionally the reverse is true, and Pawlowski found 

 that mixtures of anthrax and bacillus prodigiosus were 

 iess virulent than cultures of anthrax alone. 



