56 



MICROBIOLOGY 



to be very satisfactory. Such tubes are used for the ordin- 

 ary a gar, gellatin and bouillon cultures. Larger tubes 10 

 to 12 mm. in diameter and 10 to 12 cm. in length are com- 

 monly employed for 

 storing agar and gela- 

 tin. For plate cultures, 

 Petri dishes are usually 

 employed instead of the 

 Koch plate formerly 

 used. They are simply 

 round, double glass 

 dishes. For inoculat- 

 ing media or making 

 cultures, platinum wires 



Fig. 18. Erlenmeyer flasks, show- 

 ing different sizes and shapes; 1, 250 cc. ; 

 2, 500 cc. capacity. 



or loops attached to 

 glass rods are em- 

 ployed. A gas burner or alcohol lamp is used for steriliz- 

 ing the needle or loop. For determining the quantity of 

 gas produced by the growth of certain bacteria, the fermen- 

 tation tube of which there are several forms is used. The 

 more convenient size holds from 15 to 20 cc. The open 

 bulb should have a capacity of fully three-quarters that of 

 the closed branch. A large variety of apparatus has been 

 devised to meet the requirements of the different methods for 

 cultivating bacteria in the absence of atmospheric oxygen. 



In the preparation of culture 

 media agate iron basins and cups 

 varying in size from 0.5 to 2.0 liters 

 have been employed. Scales for 

 weighing the peptone etc. ; litmus 

 paper; one or more burettes and 

 small dishes, porcelain, for titrating 

 the media; steam and hot water cookers; water baths; 

 steam sterilizers; and autoclave for sterilizing media 

 under superheated steam are also necessary. A large 

 variety of autoclaves, steam sterilizers and water baths 

 have been made. In some laboratories the autoclave 



Fig. 19. Petri dish 

 with cover tipped. 



