DISINFECTION AND DISINFECTANTS. 217 



minutes kills them, whereas they can resist a dry heat 

 of 212° F. for several hours. More efficient than boiling 

 is live steam, especially if it is used under a pressure of 

 from one to three atmospheres. Special apparatuses 

 called auto-claves, are used for this purpose, and all 

 important sanitary stations possess such an equip- 

 ment. 



The advantages of using an apparatus in which steam 

 under pressure can be employed are three-fold : (i) The 

 penetrating power of the steam is increased; (2) since 

 the temperature of steam rises with the pressure, its 

 germicidal power is accordingly enhanced ; (3) on account 

 of the higher temperature and greater penetration, the 

 time required for disinfection is greatly diminished. 

 As a matter of fact, the bulkiness of some articles, such 

 as mattresses, bales of rags, etc., practically precludes 

 disinfection without the use of auto-claves or especially 

 devised disinfecting chambers. 



Besides steam, formaldehyde alone, or in combination 

 with steam, is used under pressure for disinfection. 

 Applied together in this way the two are more quickly 

 germicidal than either gas used alone. 



Bacteria differ in regard to the temperature required 

 to kill them. Almost all the vegetative forms are killed 

 at a temperature of (60° C, 140° F.) if applied for ten 

 minutes, and boiling (100° C, 212° F.) destroys the same 

 at once. An exception to this rule, as we have else- 

 where pointed out, is the tubercle bacillus, which, 



