STERILIZATION BY HEAT 87 



this that the temperature and time of exposure of articles 

 sterilized by this process cannot usually be controlled with 

 accuracy. It requires some time to reach a given pressure 

 after the apparatus is closed, and it also requires time for 

 cooling after the desired exposure to such pressure before 

 the apparatus can be opened. 



It is manifest that during these three periods, viz., (a) 

 reaching the pressure desired, (6) time during which the 

 pressure is maintained, and (c) time for fall of pressure 

 before the chamber can be opened, it is difficult to say 

 certainly to what temperature and pressure the articles in 

 the apparatus have, on the whole, been subjected. Clearly, 

 if the desired pressure and temperature have been maintained 

 for ten minutes, one cannot say that that is all the heat to 

 which the articles have been subjected during their stay 

 in the chamber. In this light, while steam under pressure 

 may answer very well for routine sterilization, still it pre- 

 sents insurmountable obstacles to its use in more delicate 

 experiments where time-exposure to definite temperature is 

 of importance. Nevertheless, for general laboratory pur- 

 poses, sterilization by steam under pressure has so much 

 to recommend it in the way of economy of time and cer r 

 tainty of accomplishment that it has practically superseded 

 the older methods of sterilization by streaming or live steam; 

 and in most laboratories the original styles of steam steril- 

 izers are rapidly giving way to some one or another of the 

 modern forms of autoclave. 



For sterilization by live steam the apparatus in common 

 use was for a long time the cylindrical boiler recommended 

 by Koch. (See Fig. 8.) Its construction is very simple, 

 essentially that of the ordinary domestic potato-steamer. 

 It consists of a copper cylinder, the lower fifth, approximately, 



