1020 BACTERIA IN AIR, SOIL, WATER, AND MILK 



find favorable conditions for growth and such a sample would not 

 represent fairly the supply to be tested. When the water is taken 

 from a pond, lake, or cess-pool, the bottle may be lowered into the 

 water by means of a weight, or may be plunged in with the hand, 

 great care being exercised not to permit contamination from the 

 fingers to occur. 



After the water has been collected it is important to plate it 

 before the bacteria in it have a chance to increase. The changes 

 taking place during transportation, even when packing in ice has 

 been resorted to, have been found by Jordan and Irons 6 to be 

 considerable. It is imperative, therefore, that plating of the water, 

 if possible, shall not be delayed for longer than one or two hours 

 after collection. 



Bacteriological Examination of Water. In describing the 

 methods of bacteriological examinations of water, we adhere strictly 

 to the recommendations of the Committee on Standard Methods of 

 the American Public Health Association, 7 taking the following 

 paragraphs with slight changes from their report of 1915 : 



It should be remembered that quantitative estimations of bacteria 

 in water are of most value when repeatedly done and a " normal" 

 for the particular water supply has been established, so that devia- 

 tion from this "normal" can be easily recognized. Single isolated 

 determinations may easily lead to error. 



The following paragraphs are taken without change from the 

 Public Health Association 's report : 



"Since gelatine does not give the total number of bacteria in the water, 

 the committee has thought it wise to use agar incubated at 37 C. as a 

 standard medium. This admits of counts in one day instead of two, and 

 gives results on the kind of bacteria growing at blood temperature and 

 therefore more nearly related to pathogenic types'. 



"Media. The standard medium for determining the number of bacteria 

 in water shall be nutrient agar. All variations from this medium shall be 

 considered special media. If any medium other than standard agar is used, 

 this fact shall be stated in the report. 



"For general work the standard reaction shall be +1 per cent, but for 

 long continued work upon water from the same source the optimum reaction 

 shall be ascertained by experiment and thereafter adhered to. If the reaction 

 used, however, is different from the standard, it shall be so stated in the 

 report. 



Jordan and Irons, Eeports of the Amer. Pub. Health Assn., xxv, 1889. 

 7 Amer. P. H. A., Stand. Meth. Exam. Water and Sewage, 1915. 



