166 LABORATORY METHODS OF 



find a few in the isolated state. When we have suc- 

 ceeded in obtaining a pure culture, we have only taken 

 the germ from its mixed state and have it growing on 

 a medium that is suited to its growth and development. 

 These pure cultures are absolutely necessary to a suc- 

 cessful study of the germ in question. 



The Study of the Methods of Sterilization. Heat 

 is the best, whether in the form of dry or moist heat. 

 This is the manner in which we do it : take a platinum 

 wire and heat it to a bright red, then let it cool to a 

 red heat; it is now ready to be inserted into the cul- 

 ture tube. 



All instruments are sterilized in the bunsen before 

 they are used. The glassware is sterilized by a dry 

 heat. This is done by the use of the hot-air oven. 

 Watch the demonstrator use the oven. 



The method of using the oven is simple and will 

 be used a great deal before we are through this work. 

 This method is not used in sterilizing the media as it 

 will evaporate the fluid media and scorch the solid be- 

 fore it will reach the temperature 135 degrees C. 



Sterilizing by Moist Heat. Boil the apparatus for 

 five minutes in a covered vessel, and that will insure 

 sterilizing for almost any variety of bacteria, but will 

 not kill spores; so we boil the material about twenty 

 minutes for three successive days. Steam sterilis- 



