BACTERIOLOGICAL ANALYSIS OF AIR. 613 



A sterilized aerobioscope is now to be fixed in the 

 upright position and its small end connected by a rubber 

 tube with a stopcock on the cylinder, or to a glass tube 

 tightly fixed in the neck of an aspirating-bottle by 

 means of a perforated rubber stopper. The cotton plug 

 is then moved from the upper end of the aerobioscope, 

 and the desired amount of air is aspirated through the 

 sugar. Dust-particles and bacteria will be held back 

 by the sugar. During manipulation the cotton plug is 

 to be protected from contamination. 



When the required amount of air has been aspirated 

 through the sugar the cotton plug is replaced, and by 

 gently tapping the aerobioscope while held in an almost 

 horizontal position the sugar, and with it, the bacteria, 

 are brought into the large part (e) of the apparatus. 

 When all the sugar is thus shaken down into this part 

 of the apparatus about 20 c.c. of liquefied, sterilized 

 gelatin is poured in through the opening at the end c, 

 the sugar dissolves, and the whole is then rolled on ice, 

 just as is done in the preparation of an ordinary Esmarch 

 tube. 



The gelatin is most easily poured into the aerobio- 

 scope by the use of a small, sterilized, cylindrical funnel 

 (Fig. 100), the stem of which is bent to an angle of 

 about 110 with the long axis of the body. 



The larger part of the aerobioscope is divided into 

 squares to facilitate the counting of the colonies. 



By the employment of this apparatus one can filter 

 the air at any place, and can then, without fear of con- 

 tamination, carry the tubes to the laboratory and com- 

 plete the analysis. Aside from this advantage, the filter 

 being soluble only the insoluble bacteria are left im- 

 bedded in the gelatin. 



