Bacillus Coli Communis 573 



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 i ,000,000 colon bacilli per 

 cubic centimeter and pure water very often o per cubic 

 centimeter (only i cubic centimeter 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 examina- 

 tion of i c.c. samples shows the presence of numerous colon 

 bacilli, the water is seriously polluted and doubtfully potable, 

 but when samples of i c.c. 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 intes-\ 

 tinal parasitism and taken up a saprophytic life. The 

 chief of these characters is the ability to ferment lactose/ 

 Only recently isolated organisms manifest this fermentative 

 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 detec- 

 tion of the colon bacilli in water, the favorite at the present 

 time probably being the litmus-lactose-agar plate (q. v.) of 

 Wiirtz.* 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 else- 

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



