LIQUID MEDIA. 87 



special forms of flasks, bulbs, U tubes, etc. As 

 test-tubes and flasks containing liquid media cannot 

 be inverted, inoculation with a sterilised needle must 

 be carried out as rapidly as possible, with the addi- 

 tional precaution of closed windows and doors. 



Lister's Flasks. These flasks (p. 31) were 

 especially introduced by Sir Joseph Lister as a 

 means of storing liquid nutrient media. They are 

 so constructed that after removal of a portion of 

 the contents, or restoring the vessel to the vertical 

 position, a drop of liquid always remains in the 

 extremity of the nozzle, which prevents the regur- 

 gitation of unfiltered air. 



Sternberg's Bulbs. The method of introducing 

 liquid into the bulbs employed by Professor Stern- 

 berg, and of sterilising and inoculating it, is as 

 follows : The bulb is heated slightly over the 

 flame, and the extremity of the neck, after breaking 

 off the sealed point, is plunged beneath the surface 

 of the liquid. As the air cools the liquid is drawn 

 into the bulb, usually filling it to about one-third 

 of its capacity. The neck of the flask is again 

 sealed up, and the liquid which has been introduced 

 is sterilised by repeatedly boiling the flasks in the 

 water-bath. They should then be placed in the 

 incubator for two or three days, and if the contents 

 remain transparent and free from film, they may be 

 set aside as stock-bulbs, to be used when required. 



To inoculate the liquid in the bulb the end of 

 the neck is heated to sterilise the exterior, the bulb 



