EXAMINATION OF WATER AND SEWAGE 79 



Isolation of the Typhoid Bacillus. So many difficulties attend 

 the search for the typhoid bacillus in water that it is rarely at- 

 tempted except in experimental research. Under ordinary cir- 

 cumstances the organisms do not multiply in water ; they rarely 

 live longer than seven days in cold water and even a shorter period 

 when it is warm. 



Several methods have been devised for the isolation of the 

 typhoid bacillus, one of which is the addition of large quantities 

 of water to the same volume of double-strength broth containing 

 a substance known to inhibit the growth of saprophytic organisms 

 without having an injurious effect on the typhoid bacillus. After 

 twenty-four hours pour plates are made, employing one of the 

 special media, such as the Conradi-Drigalsky. It is exceedingly 

 rare, however, that the organism is isolated. Water is more often 

 condemned on circumstantial evidence than on the actual finding 

 of the typhoid bacillus. 



Cholera Spirillum. The isolation of the cholera spirillum from 

 water is somewhat less difficult. It occurs in much greater num- 

 bers in the excreta of cholera patients than does the typhoid 

 bacillus in the feces of those suffering from typhoid fever. Koch, 

 the discoverer of the cholera spirillum, suggested a practical method 

 which has proved of value. The water to be examined is itself 

 converted into medium by dissolving in each liter ten grams of 

 peptone and sufficient sodium carbonate to make it slightly alka- 

 line. The mixture is incubated at 37 C. from sixteen to twenty 

 hours, after which gelatin or agar plates are streaked with the 

 surface growth. If cholera spirilla are present characteristic 

 colonies with irregular margins will develop which will agglutinate 

 with specific cholera serum. 



Purification of Water. Nature has various methods of her own 

 for the purification of water. Enormous quantities of sea water 

 and marsh water are being constantly evaporated and then returned 

 in the form of rain in a practically pure state. Streams tend to 

 become purer in their flow ; organic matter is gradually oxidized, 

 thus diminishing the bacterial food supply. Microscopic animals 

 such as protozoa feed upon bacteria, and they in turn serve as 



