56 DESTRUCTION OF BACTERIA BY CHEMICALS 



infectious disease, physical cleaning must be left until 

 after chemical disinfection shall have been done. It is 

 then carried out on the ordinary plan of house-cleaning. 

 The practical methods of house-disinfection today have 

 narrowed down to formaldehyde. There are many 

 forms of apparatus and several methods of producing 

 this gas, but whatever the procedure, certain conditions 

 must be observed. The temperature of air in the room 

 must not be less than 100 F., and there should be a 

 high percentage of moisture. The most common 

 method now used for the production of formaldehyde 

 gas is the mixture of 1 pint of commercial formalin 

 and 10 ounces of small crystals of potassium perman- 

 ganate in an open vessel for each 1000 cubic feet of 

 air space. These are usually mixed in the centre of the 

 room in a tall metal case of some sort, surrounded 

 by water which serves the purpose of catching any 

 of the mixture which bubbles over or extinguishing 

 fire which sometimes occurs spontaneously. The 

 cracks of doors and windows are always sealed by 

 pasting strips of paper over them. This saves much 

 of the vapor for disinfection and protects inmates of 

 other parts of the house. 



Instruments. Instruments, including syringes, may 

 be boiled for five minutes in a 1 per cent, solution of 

 washing soda. Knives, however, should be kept in 

 alcohol. Gauze should be sterilized at 120 C. or 

 248 F. and 15 pounds pressure. 



Pasteurization. This consists in the heating of a 

 substance, milk usually, to a temperature which kills 

 the non-spore-bearing bacilli, and holding there for a 

 few minutes. It is then cooled as rapidly as possible 



