EXAMINATION OF AIR, SOIL, AND WATER 223 



Varieties Found. The usual kinds found are non-patho- 

 genic, but, as is well known, typhoid, cholera, and dysen- 

 tery are principally spread through drinking-water, and many 

 other germs may find their way into the water. Some of the 

 common varieties give rise to fluorescence or produce pigment. 



Eisenberg gives 100 different varieties as ordinarily found. 

 Other intestinal diseases also are supposed to be water borne, 

 and the presence of the Bacillus coli communis means sewage 

 contamination. Ice supplies require the same supervision as 

 water supplies, for many bacteria, like the typhoid bacillus, 

 retain their vitality for weeks after freezing. 



Methods of Examination. Since the germs rapidly mul- 

 tiply in stagnant water, an examination must not be delayed 

 longer than possible after the water has been collected. Every 

 precaution must be taken in the way of cleanliness to prevent 

 contamination; sterilized flasks with glass stoppers, pipets, and 

 plugs must be at hand, and the gelatin tubes be inoculated on 

 the spot. If this cannot be done, the sample should be packed 

 in ice until it arrives at the laboratory. If it is necessary to 

 send the sample by rail, the bottle containing the sample should 

 be wrapped in sterilized cloth or the neck covered with tin- 

 foil and the bottles placed in tin boxes (about 4 ounces 100 

 c.c. is sufficient for bacterial analysis), and then packed in 

 cotton or paper to prevent breakage and surrounded by plenty 

 of ice until it reaches its destination. As soon as it arrives at 

 the laboratory the sample is placed in a sterilized glass flask, 

 and the flask then closed with a sterile cotton plug. A sterilized 

 pipet is then dipped into the flask, and i c.c. of the water with- 

 drawn and added to a tube of gelatin, the gelatin being in a 

 fluid condition. To a second tube, J c.c. is added. The tubes 

 are then shaken so as to thoroughly mix the water with the 

 gelatin, and then poured upon wide glass plates or porous 

 covered Petri dishes, one plate for each tube; the plates are 

 then placed in the moist chamber and in two or three days 

 examined. A temperature of 18 to 20 C. is best. Many 

 water-bacteria are hindered by higher degrees of heat. If the 

 germs are equally divided, there should be one-half the number 



