POUCHET'S METHOD OF ANALYSIS 



97 



may also be placed in the incubator, in order to observe the 

 micro-organisms which develop at a higher temperature. 



The method can be simplified by pouring the gelatine 

 into capsules, which, after catching the germs from the air, 

 are closed and kept. Such capsules may be exposed in a 

 glass vessel of cylindrical form, the volume of air in which 

 is known ; after a fixed time the process can be stopped, 

 and the capsules with the gelatine set aside for the organisms 

 to develop. Knowing the volume and the time of exposure, 



Connecting tube 



Aspirator 



FIG. 28. POUCHET'S AEROSCOPE. 



it is possible to gain an approximate idea of the number of 

 micro-organisms contained in the air. 



Pouchet's method. Pouchet employed for the examina- 

 tion of the dust of the air an aeroscope consisting of a glass 

 cylinder, capable of being closed air-tight by means of a 

 screw and clamps ; it is placed vertically upon a stand and 

 perforated above and below. In the upper aperture is a 

 glass tube with a very narrow exit, the lower one communi- 

 cates with an aspirator through an indiarubber pipe, and 

 in the centre of the cylinder is a little table supporting a 



n 



