110 APPLIED BACTERIOLOGY 



at any temperature which can be endured by any ordinary 

 fabric, except horse-hair, even when the organisms are 

 exposed on the surface. It is still less efficient in regard to 

 organisms below the surface ; for the penetration of the 

 heat is effected by the slow processes of conduction and 

 convection, and the external temperature cannot in practice 

 be obtained at any substantial depth. 



Wide variations of temperature occur within the dis- 

 infecting chamber, owing to unequal diffusion of the gases 

 and radiation from the heated surfaces. These facts were 

 notably demonstrated- by Koch in 1881. Cambier has 

 recently shown that the temperature and exposure for 

 merely superficial disinfection by dried heat is at least two 

 hours at 156'5° C, or one hour at 180° C. 



Hot air must therefore never be used for disinfection of 

 fabrics. Where steam is not available they may be boiled 

 for an hour in water, or an alkaline solution such as potash 

 or soda. Care must be taken to obtain and keep the tempera- 

 ture at the boiling-point throughout the mass of the water 

 and of the objects of the treatment. Before applying any 

 process of heat disinfection, stains of blood, etc., should 

 be well moistened with potassium permanganate solution 

 to prevent them from being fixed by heat. 



Heat can be most effectively applied for the disinfection 

 of fabrics by causing steam to condense in their pores. 

 More steam is sucked in to fill the place of that which has 

 been condensed, and is in its turn condensed; and the 

 process goes on till the interior of the fabrics becomes so 

 hot that no more condensation takes place ; that is to say, 

 that the temperature of the entire contents of the vessel is 

 equal to that of the incoming steam. 



Steam at any temperature or pressure which can con- 

 dense without cooling is called ' saturated steam.' Thus, 

 steam from a kettle or in a boiler is saturated. When in 



