74 BACTERIOLOGY. 



fine precipitates are said to result, and some believe 

 the reaction undergoes a change. In the experience 

 of those who have used steam under pressure not ex- 

 ceeding one atmosphere for ten to fifteen minutes these 

 obstacles have rarely been encountered. There is one 

 point to be borne in mind, however, in using steam 

 under pressure, viz., it is not possible to regulate the 

 time of exposure to the same degree of nicety as where 

 ordinary live steam is used. The reason for this is 

 that if the apparatus be opened to remove the objects 

 being sterilized while the steam within it is under 

 pressure, the escape of steam will be so rapid that all 

 fluids within the chamber, thus suddenly relieved of 

 pressure, will begin to boil violently, and, as a rule, 

 will boil quite out of the tubes, flasks, etc., containing 

 them. For this reason the apparatus must be kept 

 closed until cool, or until the gauge indicates that press- 

 ure no longer exists within the chamber, and even then 

 it should be opened very cautiously. It is patent from 

 this that the temperature and time of exposure of arti- 

 cles sterilized by this process cannot usually be con- 

 trolled 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 press- 

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

 say certainly to what temperature and pressure the arti- 

 cles 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 



