ii4 



LIQUID CULTIVATING MEDIA. 



the flame of a Bunsen burner. The test-tube is now tilted so that 

 its liquid contents come in contact with the seed material deposited 

 on its wall, and the inoculation is thus ingeniously provided for, with 

 absolutely no fear of contamination. There is no tendency for germs 

 to be wafted in from the outside atmosphere during the inoculation, 

 as the sieve-like action of the cotton wool plug provides for the 

 atmospheric pressure being equal within and without the test-tube. 



Sternberg's Bulb. 



64. Sternberg has invented another method of making pure cultiva- 

 tions in liquid media. It consists in the use of a very small glass 

 bulb with a tube opening into it. The bulb (see Fig. 59) is charged 



Fig. 59. — Sternberg's Bulb. 



by first heating it ; the tip of the tube is then broken off, and the end 

 of the tube immersed in the culture liquid. As the bulb cools the 

 liquid is drawn up into it, and usually fills about one-third of its cavity. 

 The tube is now sealed up again in the flame of a Bunsen burner, and 

 several bulbs thus charged are sterilised by intermittent heat in a water 

 or sand bath. They are then incubated for several days, and if they 

 then show no signs of contamination, they may be used in carrying on 

 cultures. In inoculating them the bulb is heated, the tip of the tube 

 broken off, and its end immersed in the material that it is desired to 

 cultivate. A trace of this at once enters the tube, and becomes 

 mingled with the liquid in the bulb. The tube is again carefully 



