124 LABORATORY BACTERIOLOGY 



EXERCISE LVI 



THE QUALITATIVE EXAMINATION OF WATER 



178. The qualitative examination of water consists in deter- 

 mining the species of bacteria present. From a sanitary stand- 

 point it consists in finding, if present, those species which may 

 be the cause of disease among people or animals consuming it. 

 The pathogenic bacteria which may be in the water will depend 

 upon the conditions ; but usually in this country water is exam- 

 ined for typhoid and hog-cholera bacilli i^B. coli communis and 

 Ps. pyocyaneus) . 



In India the spirillum of Asiatic cholera may be found in the 

 water. Occasionally anthrax may be suspected. It should be 

 stated that Ps.fiii07-escens liquefaciens, pseudo- typhoid, and the 

 transitional forms of the colon group are to be carefully dif- 

 ferentiated from Ps. pyocyaneus and B. typhosus. Owing to 

 imperfect descriptions many of the common soil and water 

 bacteria cannot be readily identified. The genera are all that 

 is expected here. 



References. Frankland, Micro-organisms in Water. Fuller, 

 Report Am. Public Health Asso., 1899, p. 580. See recent edi- 

 tions of text-books and reports of the Laboratory Section of the 

 Am. Public Health Association since 1900. 



179. Work for this exercise. Examine the cultures made 

 in Exercise LV, count the colonies on the plates, and estimate 

 from them the number of bacteria in a cubic centimeter of the 

 water ; that is, if there are 40 colonies on the plate containing 

 o.i cc. of water, there are 400 bacteria in i cc. of it. 



From the cultures in the grape-sugar media estimate the 

 number of gas-producing bacteria present. 



Describe the appearance of the different colonies and indi- 

 cate the approximate number of each kind. 



