112 BACTERIOLOGICAL LABORATORY TECHNIC 



jacket, and the interior air chamber, where the cultures are kept, 

 is thus heated to the required temperature. The amount of heat 

 is automatically regulated by a thermo-regulator, which dimin- 

 ishes the gas supply if the temperature runs too high, or increases 

 it if it runs too low. The Roux regulator is the simplest and most 

 efficient one. 



FIG. 25. Blood serum coagulating apparatus. 



A serum coagulating apparatus is needed in laboratories in 

 order to coagulate the tubes of blood serum (Fig. 25). 



Serum tubes are coagulated in it at a temperature of about 7oC. 

 They are then sterilized by heating them either by the fractional 

 method or in the autoclave. 



The separation of bacteria from the bouillon in which they 

 grow for the preparation of toxins requires the use of a bacteria 

 or germ proof filter, the best type of which is the Chamberland or 

 Pasteur unglazed porcelain filter. These filters are of varying 

 grades of fineness, and are so made as to be easily sterilized. The 

 common pathogenic bacteria cannot pass through the pores of 

 the ordinary filter, but toxic agents are known to pass through the 

 finest filters, though they cannot be discovered, as they are 

 submicroscopic. 



To operate the porcelain filter it must fit into the neck of a 



