62 PHARMACEUTICAL BACTERIOLOGY. 



Granulated sugar is loosely packed into the narrow end and aU is then 

 sterilized in a hot-air sterilizer (not over 120° C). Pass a given quantity of 

 air through the aerobioscope by, attaching an aspirator bottle to the narrow 

 end and allowing a given volume of water to run out of the bottle. The 

 volume of air drawn through equals the volume of water run from the botde. 

 Of course the cotton plug is removed from the larger end of tubeTvhile the 

 water is running. The bacilli and spores are caught in the sugar, while the 

 air passes through. Replace cotton plug and shake the sugar into the 

 larger end of tube. Remove cotton plug again and pour in about 10 to 15 

 c.c. of liquefied (40° C, not hot) gelatin. Roll the tube held horizontally. 

 The gelatin dissolves the sugar and mixes with it. Roll on ice to hasten the 

 hardening of the gelatin. Set aside in incubator, at room temperature 

 (20° C, about). The number of colonies which appear indicates approx- 



FiG. 38. — Aerobioscope after Sedgwick- Tucker, plugged with cotton. The larger 

 end in which the cultureing is done is ruled to facilitate the counting of colonies. 



imately the number of microbes in the volume of air aspirated. Let us 

 suppose that the number of colonies was 125, the volume of air aspirated 10 

 liters, from which we would get 1250 bacteria per cubic meter of air. 



F. Bacteria of Liquid Substances. — The bacteria of water, milk, tinctures, 

 fluidextracts, aquas, aerated waters, mineral waters, distilled water, broth, 

 and liquids generally, can be studied quantitatively in a comparatively simple 

 manner. By means of a sterile i c.c. graduated pipette, run o.i c.c. to 

 0.5 c.c. of the liquid into the center of a sterilized petri dish, pour upon this 

 enough (about 10 c.c.) melted, (sterile) agar or gelatin and mix by tilting 

 the dish slightly from side to side. Set aside for the medium to harden 

 and incubate at the room temperature, or at 25° C, if quicker results are 

 desired. This method is satisfactory if the number of bacilli present is 

 comparatively small. If very abundant, dilutions must be made in the 

 manner already described. 



The follovidng general suggestions should be observed in making bacterio- 

 logical determinations of liquids: 



a. Containers for samples (other than the original containers) must be 

 sterile and closed with sterile corks or cotton plugs. If the samples are to 

 be carried any distance they should be packed in ice. In no case is it wise to 

 keep a sample longer than forty-eight hours before culturing it. If the 

 sample is to be examined within two or three hours after collecting it, 

 placing on ice is not absolutely necessary. 



