CHEMICAL STERILIZATION AND DISINFECTION. 81 



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 had constructed some years ago 

 a sterilizer in all respects similar to the old form except 

 in the arrangement of the copper bottom. This latter 

 is made in such a way that it can easily be removed, so 

 that by keeping several sets of copper plates on hand a 

 new plate 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 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 dimmish 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. 



THERMAL DEATH-POINT OF BACTERIA. By " ther- 

 mal death-point of bacteria " is meant the temperature 

 necessary to kill them in a given time. As this varies 

 with different species, it is an aid to identification. For 

 the practical purposes of the sanitarian the knowledge is 

 of fundamental importance. The thermal death-point of 



