64 BACTERIOLOGY. 



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 

 forms 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 made in 

 such a way that it can be easily removed, so that by 

 keeping several sets of copper plates on hand a new one 

 can readily be inserted 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 steril- 

 ized stand results not only in destruction of the appa- 

 ratus, but frequently in destruction of the substances 

 undergoing sterilization. 



Since the temperature at which this form of steril- 

 ization is usually accomplished is high, from 150° to 

 180° C, it is well to have the apparatus encased in 

 asbestos boards, to diminish the radiation of heat from 

 its surfaces. 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 



