244 BACTERIOLOGY. 
entirely useless for bacteriological investigations. It 
cannot be too much emphasized that materials which 
are not immediately used should be sent to the labora- 
tory as quickly as possible, for in such substances as 
feces, where enormous numbers of various kinds of 
bacteria are present, those which we seek most, such as 
the typhoid bacilli, frequently succumb to the delete- 
rious products of the other bacteria present. Even 
when abundantly present living typhoid bacilli may 
entirely disappear from the feces in the course of even 
twelve hours, while at other times they may remain 
present for weeks. These differences depend on the 
associated organisms present, the chemical constitution 
of the feces or urine, and the conditions under which 
the material is obtained. 
