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A MANUAL OF BACTERIOLOGY 



air are rapidly deposited within the tube, and on the 

 surface of the gelatine give rise to colonies. Fig. 

 52 represents Hesse's aeroscope. At D is an india- 

 rubber stopper, perforated to admit a small glass 



Fig. 52. HESSE'S AEROSCOPE. 



tube, plugged with cotton-wool ; and at the opposite 

 end is a perforated indiarubber cap, which is 

 covered by an imperforated cap (C) of the same 

 material. The aspirator consists of two like flasks 

 (A B); one of which is filled with water. These 

 flasks are reversible ; but the one containing the 



