60 BACTERIOLO&r. 



copper plates placed one above the other, but with a 

 space of about 4 to 5 mm. between the plates. These 

 copper bottoms after a time become burned out, and 

 unless they are replaced the apparatus is useless. The 

 older form of hot-air sterilizers are so constructed that 

 their repair is a matter involving some time and expense. 

 To meet this objection I have had constructed a steril- 

 izer in all respects similar to the old form except in the 

 arrangement of this copper bottom. This is so made 

 that it can be easily slipped in and out, so that by 

 keeping several sets of copper plates on hand a new one 

 can readily be slipped into the apparatus when the old 

 one is burned out. 



In the employment of the hot-air sterilizer care should 

 always be given to the condition of the copper bottom ; 

 for the direct application of the heat to the sheet-iron plate 

 upon which the substances to be sterilized stand results 

 not only in destruction of the apparatus, but frequently 

 in destruction of the substances undergoing sterilization. 



Since the temperature at which this form of steriliza- 

 tion is usually accomplished is high — 150° to 180° C. 

 — it is well to have the apparatus encased in asbestos 

 boards, to diminish the radiation of heat from its sur- 

 faces. This not only confines the heat to the apparatus, 

 but guards against the destructive action of the radiated 

 heat on woodwork, furniture, etc., that may be in the 

 neighborhood. 



CHEMICAL STERILIZATION AND DISINFECTION. 



As has already been stated, it is possible by means 

 of certain chemical substances to destroy all bacteria 

 and their spores that may be within or upon various 



