15 



CHAPTEK II 



PRELIMINARY PROCESSES APPARATUS AND REAGENTS 



Sterilisation is the process by which both instruments 

 and culture-media are freed from hving germs, and is 

 carried out in different ways. 



Sterilisation by heat. — Articles capable of withstanding 

 a very high temperature are best sterilised by being held 

 in the flame of a Bunsen burner or spirit-lamp until a 

 red or white heat is reached, a method which is especially 

 applicable to small platinum wires or plates. 



Bodies which have no great power of resistance, and 

 instruments which could not be exposed to so intense a 

 heat without impairing their efficiency and sharpness, are 

 subjected for a longer time to a temperature of 150° C, by 

 which both the micro-organisms and also their spores are 

 destroyed. For this purpose a box made of sheet iron, 

 with double walls, is best employed, which has thus a 

 layer of air between the walls {hot-air steriliser). It must 

 be put together with rivets, not with solder. By means of 

 a single powerful burner or a number of small ones placed 

 beneath, the temperature of the interior is rapidly brought 

 to 160°- 170°, after which half an hour suffices for sterilisa- 

 tion. In the top of the box are openings for two ther- 

 mometers, one of which extends into the interior, while 

 the other registers the temperature of the space between 

 the inner and outer walls ; and there is also a valve for 



