234 



NA TURE 



[July 5, 1888 



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Fir:. 1. — Glass tube through which the air is aspirated: about the original size, a, aperture of tube through which the aspirated air enters; B, exit of 

 aspirated air ; a, first filter-plug, consisting of glass-wool ; i, second filter-plug, consisting of glass-wool and powdered glass or sugar ; c, cotton- 

 wool plug to protect plug b. 



Fig. 2.— Arrangement of the apparatus for taking a sample of air. a, n, the filter tube; c, lead tubing, about 10 feet in length; d, mercury pressure- 

 gauge ; b, air-pump. 



Tig. 3.— Flasks after incubation, showing colonies on film of gelatine with which the inner surface is coated, 



