114 BACTERIOLOGICAL METHODS 



13. Biological Water Analysis 



The complete biological analysis of water supplies is, as a rule, 

 not a regular routine of the food and drugs bacteriologist, yet he 

 should be prepared to make such analysis when occasion makes 

 it necessary. The food bacteriologist will have to do more with 

 the analysis of sewage contaminated water supplies and with 

 foods and other substances which have come in contact with such 

 contamination. 



The complete biological analysis of water supplies may be out- 

 lined as follows the fuller details of which may be found in special 

 text-books, bacteriological journals and reports on water analysis. 



Securing the sample. 

 Bacteriological examination. 



Quantitative. 



Qualitative; the presumptive colon bacillus test. 

 Algae; significance of. 



Diatoms. 



Desmids. 



Nostoc and oscUlaria. 



Other algae. 

 Molds and spores; significance of. 

 Ova and larvae of higher parasites; significance of. 

 Sand, dirt, etc. 



The water supply of a city or community should be watched 

 at all times, but perhaps more particularly in the early spring when 

 the melting snows and the heavy rains bring in materials accumu- 

 lated and held back during the winter months. Furthermore, the 

 rise in temperature encourages the rapid multiphcation of various 

 organisms, such as algae and bacteria. In late summer and early 

 fall the drinking water often becomes vitiated, through a reduction 

 in supply, perhaps as the result of lack of rainfall. In the early 

 spring, after the first days of warm weather, the water supply often 

 becomes murky due to dirt washed in, green in tint due to the 

 enormous development of algas and generally accompanied by a 

 decidedly disagreeable odor which is traceable to the presence of 



