90 PHARMACEUTICAL BACTERIOLOGY 



F. Bacteria of Liquid Substances. The bacteria of water, milk, tinc- 

 tures, fluid extracts, aquae, aerated waters, mineral waters, distilled water, 

 broth, and liquids generally, can be studied quantitatively in a compara- 

 tively simple manner. By means of a sterile i cc. graduated pipette, 

 run o.i cc. to 0.5 cc. of the liquid into the center of a sterilized petri dish, 

 pour upon this enough (about 10 cc.) 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 37 C., as may be 

 required. 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 following general suggestions should be observed in making bac- 

 teriological determinations of liquids : 



FIG. 38. Aerobioscope after Sedgwiek- Tucker, plugged with cotton. The larger end 

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



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. 



b. Every sample should be thoroughly mixed before making cultures. 

 Shake well, about twenty times. This is very important. 



c. All glassware, pipettes, etc., must be thoroughly sterilized by wash- 

 ing, rinsing, wiping, hot air or steam sterilization, etc. 



d. The methods of making dilutions, the amounts to be planted or 

 tubed, the culture media to be used, etc., etc., cannot be given in detail in 

 a work of this kind. All will depend upon the kind of analysis to be 

 made, the results to be attained, etc. The special methods to be em- 

 ployed in special cases must be looked up in suitable text-books and 

 carefully followed. The following general suggestions are in order at this 

 time. 



e. Thus far there are no standards for the bacteriological testing of 

 Pharmaceuticals. Tinctures and fluidextracts should show only few 

 colonies per cc., not over 30 to 60. Sera should show none. Well pre- 

 pared and properly ripened small-pox vaccine should show only a few 

 colonies, from 20 to 500, per ivory point or per tube. 



