176 MICROBIOLOGY 



Objects of water analysis. Water is analyzed bacteri- 

 ologically to determine : ( 1 ) the number of bacteria per cubic 

 centimeter and (2) the kinds of bacteria. In addition to the 

 soil, water and fecal organisms certain pathogenic bacteria 

 may be present. These are largely the bacteria that produce 

 intestinal disorders, the most common of which are the bacillus 

 of typhoid fever, the microspira of Asiatic cholera and Pseudo- 

 monas pyocyaneus. Sometimes those of other diseases such 

 as anthrax may gain access to water. Water is often the 

 channel through which many pathogenic bacteria gain en- 

 trance to the human and animal body. 



Methods of water analysis. In making water analyses 

 great care must be taken in carrying out the details in: (1) 

 collecting the samples and (2) the water must be collected in 

 clean, sterile vessels such as sterilized bottles. Various de- 

 vices are used for collecting it at different levels. The cul- 

 ture media to be used and the time for observing cultures 

 before counting colonies are important. The media and 

 methods vary according to the conditions and specific purpose 

 of the examination. 



Chamot and Redfield 3 recommend the following respect- 

 ing cultures, temperatures and time for examination. They 

 give many other media for the determination of special prop- 

 erties and identification of species. 



"Gelatin plates at 20 C. in air. At least two with 1 cc. 

 each ; two with 0.1 cc. each and if the water is believed to be 

 very bad, two with 0.01 cc. each." 



" Agar plates kept at 20 C. At least two with 1 cc. each, 

 two with 0.1 cc. each. 



"Agar plates kept at 38 C. Two with 1 cc. each; two 

 with 0.1 cc. each. 



"Agar lactose litmus, incubated at 38 C. Two tubes with 

 1 cc. each; two tubes with 0.1 cc. each. This consists in 

 adding from 3 to 5 drops of sterile litmus solution to the warm 

 liquefied lactose agar just before pouring into the Petri dishes. 



3 Chamot and Redfield. Analysis of Water for Household and 

 Municipal Purposes. Ithaca, 1911. 



