THE BACTERIA OF SOIL, AIR, WATER, ETC. 131 



in a good water-supply, any sudden variation above that num- 

 ber is to be looked upon with suspicion as indicating a pos- 

 sible surface contamination. 



The bacteriological examination should always be accom- 

 panied by a chemical examination, and by an inspection of 

 the surroundings. A large number is to be expected when 

 the water has been subjected to unusual agitation from winds 

 or currents which stir up the bacteria which have settled. 



The detection of pathogenic bacteria in water * involves 

 great difficulties, and our knowledge in this direction is very 

 meagre. Koch and several others have reported finding the 

 spirillum of Asiatic cholera in water. The examination of 

 water-supplies for this organism has disclosed the fact that 

 bacteria resembling the organism of cholera in many respects 

 are not uncommon in water. This adds to the difficulty of 

 detecting the cholera germ in water. 



The bacillus of typhoid fever has many times been de- 

 scribed as occurring in water-supplies suspected of being con- 

 taminated with the excreta of cases of the disease. The inter- 

 pretation of these observations is at present doubtful.f It is 

 now known that several forms of bacteria exist which closely 

 resemble the bacillus of typhoid fever, and which make its 

 recognition in an unknown specimen very difficult. J 



It will at once be appreciated that the number of cholera 

 and typhoid organisms necessary to contaminate a consider- 

 able body of water, and sufficient to cause an outbreak of the 

 disease among some of the people drinking the water, may 

 still be so small that many different cubic centimeters of the 

 water might be studied before a single one of the specific organ- 

 isms would be encountered. Anyone who has examined plates 



* See also articles in Part IV. on the bacillus of typhoid fever, bacillus coli 

 communis and spirillum of cholera. 



f Consult editorial. Journal American Medical Association. Dec. 5, 1903. 

 J For methods of detection see under Typhoid Bacillus, p. 301. 



