56 DESTRUCTION OF BACTERIA BY CHEMICALS 



and lysol. The two latter are probably the best, as 

 they mix with water fairly well. All these substances 

 in 5 per cent, emulsion kill the ordinary bacteria 

 within three minutes and the spore-formers within an 

 hour. 



Other Disinfectants. Ordinary alcohol kills vegeta- 

 tive forms in a few hours. A 70 per cent, alcohol is 

 perhaps the most potent. It has lately been shown 

 that for surface disinfection no method is superior to 

 10 per cent, iodine in 70 per cent, alcohol. Practical 

 surgical work seems to indicate that for skin disin- 

 fection before operation all bacteria are destroyed 

 in the epidermis. Some defenders of this method 

 maintain that its penetrating powers exceed any 

 other known practical disinfectant. The method, 

 while undoubtedly excellent, must remain for a while 

 su~b judice before one can accept this statement. 

 Chloroform kills vegetative bacteria and restrains 

 spores, even in small quantities. Ordinary soap is a 

 good disinfectant, particularly by its solvent power 

 on the simple organic substances. Its effect is increased 

 by the addition of common washing soda. 



Acids. The strong mineral acids are not practical 

 disinfectants, but nevertheless are very efficient. Boric 

 acid kills the less resistant organisms in a 2 per cent, 

 solution, but only after some hours' exposure. 



Gaseous Disinfectants.- There are only three of 

 practical value. They are sulphur dioxide, oxygen 

 from hydrogen dioxide, arid formaldehyde. Chlorine 

 is not included here because it is seldom used in its 

 pure state, since it is highly poisonous and destructive ; 

 it is, however, eminently efficient. 



