AIR AND WATER. 61 



microscope. This method is defective in so far as it gives 

 no information on the most important point namely, which 

 and how many of the intercepted germs are actually capable 

 of development. 



In order to determine the number of germs capable of 

 development, and also their nature, Miquel employs the 

 following apparatus (Fig. 15) : The flask A has fused into 

 it a tube, R, tapering below and nearly reaching to the bottom ; 

 the upper end of this is fitted with a ground cap, H, provided 

 with a narrow filter- tube containing sterilised cotton-wool, 

 asbestos, or glass-wool, as. On one side of the flask is a tube, 

 Asp, which is constricted in the middle, and is provided with 

 two cotton-wool plugs, w and w. On the other side is another 



Fig. 14. Acroscope. Fig. 15. Miquel's apparatus for 



air analysis. 



glass tube connected by rubber, k, with the tube B, which is 

 drawn out to a point, and closed by fusing the end. The 

 flask is partly filled with distilled water, and the whole appar- 

 atus sterilised. When the apparatus is to be used, the tube 

 Asp is connected with an aspirator (e.g., a bottle filled with 

 water and provided with an outlet cock) ; the cap H is taken 

 off, and the air then passes, bubble by bubble, through the 

 opening o, through the water g, and out through the cotton- 

 wool plugs of the tube Asp. Since all the germs in the air 

 are not retained by the water when the air-bubbles ascend 

 through the latter, the cotton-wool plug w is intended to catch 

 those which get past the water. When the experiment is 

 finished, the cap H is replaced over the tube JR. By blowing 

 through Asp, the liquid is made to ascend in E, in order that 



