CHAPTER XVIII. 



SPECIAL 

 BACTERIOLOGICAL EXAMINATIONS. 



BACTERIOLOGICAL EXAMINATION OF WATER. 

 IN all natural unfiltered waters, except when derived 

 from deep wells and springs (in which case nitration has 

 already taken place through the strata) numbers of bacteria 

 are found. The actual content is determined by the 

 accumulated action of the following factors, namely : 



1. Presence or absence of local pollution. 



2. Presence or absence of natural purification. 



3. The season of the year. 



4. The rainfall at any particular period. 



The bacteria found in water may likewise be classed 

 under four heads, as 



1. Harmless : the natural water bacteria. Such are the 

 B. fmorescens liquefaciens, B. fluorescens non-liquefaciens, 

 B. prodigiosus, B. violaceus, sarcinae, and spirilla. These 

 all grow best at room temperature. 



2. Unobjectionable : those present from soil washings, 

 as B. subtilis, B. mycoides, and B. megatherium. 



3. Objectionable : those derived from sewage, either 

 directly or from sewage-polluted soil. Such are : (a) The 

 B. proteus group ; (b) B. coli communis and its allies ; 

 (c) Streptococci ; (d) Staphylococci ; (e) B. enteritidis 

 sporogenes. 



4. Dangerous : those capable of causing infection by the 

 alimentary canal. Such are the B. typhosus, B. para- 

 typhosus, B. dysenteriae, and Sp. choleras. 



Samples. Stoppered sterile glass bottles should be 

 used for sampling, each of at least 250 c.c. capacity (8 to 

 10 oz.). The bottle should be thoroughly cleansed with 

 soap and water, well rinsed with clean water, and sterilized 

 (inverted and with stopper out) in steamer for one hour. 



