AGENTS PREJUDICIAL TO BACTERIAL LIFE 1 9 



FREE AGENTS PREJUDICIAL TO THE LIFE OF 

 BACTERIA. 



High temperatures are surely germicidal: 60 C. coagulates 

 mycoprotein of bacteria and other common albumins. The degree 

 of temperature at which bacteria are killed is called the thermal 

 death^oml. Most vegetative forms die after a short exposure at 

 60 C., though some require a higher temperature, e.g., tubercle 

 bacillus. 



,' Spores resist boiling, often for hours. Spore-bearing bacilli from 

 the soil often survive a temperature of 115 C. moist heat (steam), 

 from thirty to sixty minutes. Bacteria resist dry heat of 175 C. 

 from five to ten minutes. 



y Cold inhibits bacteria; destroys some; but is not a safe germicidal 

 agent, as typhoid bacilli have been isolated from melted ice in which 

 they had been frozen for months. ^ 



Ravenel exposed bacteria to the extreme cold of liquid air ( 312 

 F.) and found that typhoid bacilli survived an exposure of sixty 

 minutes; diphtheria, thirty minutes, and anthrax spores, three hours; 

 during this exposure, however, many were destroyed. In each 

 instance, vegetative forms grew after the exposure. 

 Light is inimical to the life of bacteria; direct sunlight being the 

 most germicidal, as it destroys some, reduces the virulence of others, 

 or interferes with the chromogenic properties. Typhoid, cholera, 

 diphtheria, and many other organisms are killed after an hour or 

 two's exposure to bright sunlight. The ultraviolet or actinic rays 

 are the efficient ones. If free oxygen is excluded, the germicidal 

 action is very materially reduced. Sunlight acting on culture media 

 (free oxygen and water being present) produces after ten minutes, 

 peroxide of hydrogen. This action of light on bacteria has been 

 extensively used, notably by Hansen, as a therapeutic measure for 

 the cure of bacterial skin diseases, especially lupus. Diffuse sun- 

 light, electric light, Rcentgen-rays, continuous and alternating 

 currents of electricity, are also more or less germicidal. Anti- 



