Bacilli Resembling the Typhoid Bacillus 623 



It is a speculation whether the colon bacilli were originally micro- 

 organisms of the soil that accidentally found their way into the con- 

 genial environment of the intestine and there took up permanent 

 residence, or whether they have always been intestinal parasites and 

 have been discharged with the excrement of animals until the soil 

 has become generally infected with them. However this may be, 

 they are at present found in the intestinal canals of all animals, and 

 in pretty much all soils, their number being greatest in manured soils. 

 From the soil it is inevitable that the organisms shall pass into the 

 surface waters, which with few exceptions will be found to contain 

 them. The numbers, however, can be made use of to indicate the 

 quality of the water, a few organisms indicating that the water is 

 pure, many that it is freely mixed with surface washings. 



As sewage contains as many as 1,000,000 colon bacilli per cubic 

 centimeter and pure water very often o per cubic centimeter (only 

 i cc. being examined at a time), the number of bacilli per cubic 

 centimeter can be expressed as indicating the amount of sewage 

 pollution. The number of colon bacilli in the water is, therefore, of 

 importance in determining its potability, and in cases in which 

 the quality of the water is doubtful, should always be employed. 

 There is no infallible criterion for judging the quality of water, but 

 most American bacteriologists are in accord in concluding that when 

 the repeated examination of i cc. samples shows the presence of 

 numerous colon bacilli, the water is seriously polluted and doubtfully 

 potable, but when samples of i cc. are without colon bacilli or contain 

 very few, the water is safe. 



Another important matter in regard to the colon bacillus in water is 

 the presence or absence of certain characters by which one can judge 

 how recently it has ended its intestinal parasitism and taken up a 

 saprophytic life. The chief of these characters is the ability to fer- 

 ment lactose. Only recently isolated organisms manifest this fer- 

 mentative power in the laboratory, so that when organisms capable 

 of fermenting lactose are found, one can suppose that they result 

 from recent sewage pollution. 



Many media have been recommended for the rapid detection of the 

 colon bacilli in water, the favorite at the present time probably be- 

 ing the litmus-lactose-agar plate (q.v.) of Wlirtz. * This depends upon 

 the fermentative and acid-producing power of the bacillus, which is 

 shown through the presence of red colonies (acid producers) on the 

 elsewhere blue plate. These red colonies are then fished up and trans- 

 planted to appropriate media for further study. 



Kline | substitutes lactose for the glucose in this medium, pointing 

 out that by so doing one at once differentiates between typical colon 

 bacilli which ferment lactose and atypical varieties which do not. 



* "Archiv. de m6d. Experimentale," 1892, iv, p. 85. 

 t "British Medical Journal," Oct. 27, 1906, p. 1090. 



