112 PRINCIPLES OF BACTERIOLOGY 



Peroxide of hydrogen (H 2 O 2 ) is an energetic disinfectant, and in 2 

 per cent, solution (about 40 per cent, of the ordinary commercial 

 article) will kill the spores of anthrax in from two to three hours. A 

 20 per cent, solution of a good commercial hydrogen peroxide solution 

 will quickly destroy the pyogenic cocci and bther spore-free bacteria. 

 It combines with organic matter, becoming inert. It is prompt in its 

 action and not poisonous, but apt to deteriorate if not properly kept. 



Chlorine. Chlorine is a powerful gaseous germicide, owing its activity 

 to its affinity for hydrogen and the consequent release of nascent oxygen 

 when it comes in contact with micro-organisms in a moist condition. 

 It is, therefore, a much more active germicide in the presence of moisture 

 than in a dry condition. Thus, Fischer and Proskauer found that 

 dried anthrax spores exposed for an hour in an atmosphere containing 

 44.7 per cent, of dry chlorine were not destroyed; but if the spores were 

 previously moistened and were exposed in a moist atmosphere for the 

 same time, 4 per cent, was effective, and when the time was extended 

 to three hours 1 per cent, destroyed their vitality. The anthrax bacillus, 

 in the absence of spores, was killed by exposure in a rnoist atmosphere 

 containing 1 part to 2500 for twent}^-four hours. 



In watery solutions 0.2 per cent, kills spores within five minutes and] 

 the vegetative forms almost immediately. 



Chloride of Lime. The efficacy of chloride of lime depends on the 

 chlorine it contains in the form of hypochlorites. A solution in water 

 of 0.5 to 1 per cent, of chloride of lime will kill most bacteria in one to 

 five minutes. A 5 per cent, solution usually destroys spores within one 

 hour. 



Bromine and iodine are of about the same value as chlorine foij 

 gaseous disinfectants, in the moist condition; but, like chlorine, they 

 are not applicable for general use in house disinfection, owing to their 

 poisonous and destructive properties; they have a use in sewers and 

 similar places. 



Trichloride of iodine in 0.5 per cent, solution destroys the vegetative; 

 forms of bacteria in five minutes. 



Organic Disinfectants. 



Alcohol in 10 per cent, solution inhibits the growth of bacteria; 

 absolute alcohol kills bacteria in the vegetative fornT~>n from several 

 to twenty-four hours. 



Formaldehyde. Formaldehyde, or formic aldehyde, was isolated 

 by von Hoffmann in 1867, who obtained it by passing the vapors of 

 methyl-alcohol mixed with air over finely divided platinum heated to 

 redness. The methyl-alcohol is oxidized and produces formaldehyde 

 as follows: 



CH 2 OH + O = CH 2 H 2 0. 



Formaldehyde is a gaseous compound having the chemical formula 

 CH 2 O and possessed of an extremely irritating odor. At a temperature 

 of 68 F. the gas is polymerized that is to say, a second body is formed, 



