DISINFECTION BY HEAT 363 



neglected. The usual disinfectant has been mercuric 

 perchloride 1 in 1,000 acidulated, or with salt added (3 to 5 

 per cent.). Of late formaldehyde solution has been used 

 with excellent results. 



This method is indicated with formaldehyde solution for 

 cases where an offensive odour exists, the solution being a 

 strong deodorant. It is also tlie best means available for 

 disinfecting furs and leather articles, which cannot stand 

 the action of steam. 



Disinfection by Heat. — Hot air does not kill all organisms 

 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 

 temperature 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 perman- 

 ganate solution to prevent them from being fixed by 

 heat. 



