TESTS FOR B COLI 299 
tration or evaporation under reduced pressure at low temperatures. 
Decimal dilutions of this concentrated sample shoulu be made and 
1 c.c. quantities added to sterile litinus milk. It is a ggod plan to boil 
the tubes of milk for about five or ten minutes before inoculating in 
order to expel as much air as possible. After the tubes have been 
inoculated they should be heated on a water bath at 80° C. for twenty 
minutes which will kill all vegetative forms. They are then incubated 
under anaerobic conditions either in a Novy jar or made anaerobic by 
the Wright method. 
The Bacillus Colon Test. Escherich isolated Bacillus colon soon 
after the discovery of solid media by Koch. Escherich was attempting 
to find the causal organism of cholera. At first it was thought that he 
had found the specific bacterium which caused cholera because Bacillus 
colon was found to be present in the intestinal tract of each patient. 
This, however, was soon found to be untrue for the bacillus was found 
in the intestinal tract of normal individuals. Later investigations 
indicated that it was always present in the feces and from these facts 
bacteriologists attempted to use it as the indicator of the presence of 
fecal matter in foods even though the amount was very small. For 
some time it was accepted as a reliable factor in bacteriology but as 
knowledge was supplemented with more data it became apparent that 
some limitations had to be placed in interpreting this test. Much of 
our work since this time has been concerned with studies to find out the 
limits in the value of Baczllus colon in this connection. 
Different definitions have been given for the Baczllus colon group. 
Standard Methods (1917) recommended that the B. colt group be con- 
sidered as including all non-spore-forming bacilli which ferment lactose 
with gas formation and grow aerobically on standard solid media. 
The value of the B. coli test has been discredited by some of the prac- 
tical waterworks men. They argue from the several researches which 
have shown that the organism may not at all times be restricted to 
sources which have received sewage pollution. Rogers, Clark and Evans 
(1915), Prescott (1906), Metcalf (1905), Smith (1905), and others have 
reported the organism or B. coli like organisms from grain fields and 
grains which had not received sewage pollution. Their work was of 
such import that it became necessary to distinguish between fecal and 
non-fecal B. cola. The English and American bacteriologists have 
regarded the B. coli test with favor while some German bacteriologists 
have fought its use. Kruse (1894), for instance, believes that B. coli 
may be found in any water no matter from what source, provided a large 
enough sample is taken. Chick, representing the English opinion, believes 
