Methods of Determination of Pathogenic Microbes. 117 



for the sterilization of culture media, and for objects 

 which can not sustain a temperature of 150°. 



d) Papin's steamer — The Chamherland autoclave. — 

 Sterilization of objects in fluid media is much more 

 rapid and certain when they are subjected during ten 

 to fifteen minutes to a temperature of 120°. To 

 realize these conditions the objects are inclosed in a 

 Papin steamer, which admits of obtaining, under 

 pressure, the temperature indicated. 



Chamherland has recently devised an autoclave or 

 steamer specially adapted for sterilization. It is now 

 found in all laboratories. It is merely a Papin 

 steamer modified for this particular use. 



e) Discontinuous heating. — Some media, such as 

 blood serum and milk, can not endure a temperature 

 of 100° without undergoing considerable modifica- 

 tions. For the sterilization of these substances we 

 have recourse to the method of Tyndal, which con- 

 sists in killing the germs in full vegetation, an ope- 

 ration which only requires a temperature of 58°, 

 maintained during two hours. For blood serum the 

 temperature should not exceed 58°, for this medium be- 

 comes coagulated at a higher temperature. The first 

 heating not having killed the spores, the substance is 

 then brought to the ordinary room temperature, or 

 better, to 37°; the spores then quickly vegetate and 

 the bacteria to w^hich they give birth will be killed 

 by a second heating on the following day. This ope- 

 ration, repeated four or five times, ends in the certain 

 sterilization of the liquid. 



The apparatus employed in this method of steril- 

 ization consists of water baths maintained at a con- 

 stant temperature by a regulator. 



