26 



BACTERIOLOGY FOR NURSES 



air thus heated surrounds the inner chamber and escapes through 

 holes in the top of the outer case. The bulb of the thermometer 

 used to record the temperature should pass about to the center 

 of the inner chamber. Heating for one hour at 150 C. is sufficient 

 to insure sterilization. Articles should be placed in the hot air 

 chamber, without crowding, before heating it and should be allowed 



to remain there after sterilization is 

 complete until the temperature falls. 

 Sudden heating or cooling may cause 

 the glass to crack. 



2. Red Heat. Platinum needles are 

 sterilized by flaming in a Bunsen burner 

 until they are red hot. The points of 

 forceps, coverlips, and glass slides may 

 also be sterilized by passing through a 

 Bunsen flame. 



STERILIZATION BY MOIST HEAT 



1. Boiling. The boiling of water for 

 five minutes is sufficient to insure steri- 

 lization if no spores are present. Steel 

 instruments should be placed in a boiling 

 solution of 1 per cent sodium carbonate 

 for at least five minutes. 



2. Steam at High Pres- 

 sure. The most rapid and 

 effective means of steriliza- 

 tion is accomplished by steam 

 under pressure in an autoclave (Fig. 6). The apparatus consists 

 of a metal cylinder supported in an iron case ; it is fitted with a 

 pressure gauge, thermometer, and safety valve ; its cover can be 

 securely fastened down with nuts and screws. The articles to 

 be sterilized are supported on a perforated diaphragm, and heat 

 to generate the steam is supplied by a large Bunsen burner 

 beneath. The temperature usually employed is 115 C. to 120 

 C. In order to obtain a temperature of 115 C. a pressure of 



FIG. 6. Autoclave. 



