158 BACTERIOLOGY. 



The Effect of Acids. An amount of acid which equals 

 40 c.c. of normal hydrochloric acid per litre is sufficient 

 to prevent the growth of all varieties of bacteria and 

 to kill many. Twice this amount destroys most bacteria 

 within a short time. The variety of acid makes little 

 difference. Bulk for bulk, the mineral acids are more 

 germicidal than the vegetable acids, but that is because 

 their molecular weight is so much less. A 1 to 500 

 solution of sulphuric acid kills typhoid bacilli within 

 one hour. Hydrochloric acid is about one-third weaker, 

 and acetic acid somewhat weaker still. Citric, tartaric, 

 malic, formic, and salicylic acids are similar to acetic 

 acid. Boric acid destroys the less resistant bacteria in 

 2 per cent, solution and inhibits the others. 



GASEOUS DISINFECTANTS. 



The germicidal action of gases is much more active 

 in the presence of moisture than in a dry condition. 



Numerous experiments have been made with sulphur 

 dioxide gas (SO 2 ), owing to the fact that it has been so 

 extensively used for the disinfection of hospitals, ships, 

 apartments, clothing, etc. This gas is a much more 

 active germicide in a moist than in a dry condition; 

 due, no doubt, to the formation of the more active disin- 

 fecting agent sulphurous acid (H 2 SO 3 ). In a pure state 

 anhydrous sulphur dioxide does not destroy spores, and 

 is not certain to destroy bacteria not in spore form. 

 Sternberg has shown that the spores of the bacillus 

 anthracis and bacillus subtilis are not killed by contact 

 for some time with liquid SO 2 (liquefied by pressure). 

 Koch found that various species of spore-bearing bacilli 



