DISINFECTION BY HEAT 753 



as stables, pens, yards, etc., flaming with a painter's 

 blow-lamp may be employed. If the surfaces be first 

 sprayed with water, risk from fire is practically abolished, 

 and the operator soon acquires experience as to the 

 duration and amount of flaming. 



Dry heat may also be used, and forms the basis of some 

 disinfectors (Ransome's), but is not nearly such an efficient 

 means as moist heat. The objections to dry heat are, 

 that to ensure the destruction of bacteria and spores the 

 temperature must be high and the heating prolonged. 

 Koch and Wolfhiigel found that two hours at 150 C. did 

 not always ensure sterilisation, and Gaffky and Loftier 

 state that the spores of some organisms are killed only 

 by exposure to hot air at 140 C. for three hours. More- 

 over, dry heat has little power of penetration, and it 

 requires many hours for the centre of a mass of bedding, 

 or the like, to attain the temperature requisite for sterilisa- 

 tion, while some articles and fabrics are distinctly injured 

 by the prolonged heating. The highest temperature which 

 can be safely adopted for a dry-heat disinfector is about 

 120 C., and then if large masses have to be treated the 

 heating has to be continued for from eight to ten hours. 

 A rise of 5 C. above this temperature is sufficient to 

 damage many woollen goods, which enhances the objec- 

 tions to a dry-heat disinfector, as it is difficult to keep the 

 temperature of a large chamber constant. 



For the reasons given above, disinfection by dry heat 

 is often impracticable ; on the other hand, moist heat is 

 more effective, is found to work well in practice, and is 

 now generally adopted. In the household, for articles 

 which cannot be burnt, brisk boiling for an hour or so will 

 suffice. 



Steam disinfection. For public disinfectors, steam under 

 pressure i.e. at a pressure greater than that of the atmo- 

 sphere : is employed. Steam under pressure has not such 



M.B. 48 



