56 BACTERIOLOGY. 



tured appendix. Occasionally it causes a general in- 

 fection. The poisons of the colon bacillus are con- 

 tained within the body of the organism and are 

 liberated only when it disintegrates. The knowledge 

 of this fact has made it possible to immunize against 

 colon infections by injecting the dead cultures, or 

 vaccine, in slowly increasing doses. (See Immunity.) 

 On account of its constant presence in the intes- 

 tine of man and animals, the presence of the colon 

 bacillus in water or milk leads to the assumption that 

 they have become infected with intestinal discharges, 

 and so not' safe for consumption. On account of the 

 wide distribution of the colon bacillus in nature, this 

 view has been modified to some extent, and now, 

 unless they are present in excessive number, the water 

 or milk is not condemned. 



THE BACILLUS TYPHOSUS. 



The typhoid bacillus is the cause of typhoid fever. 

 In recent years we have come to* recognize that there 

 are a number of other micro-organisms closely related 

 to the typhoid bacillus which produce a fever and other 

 symptoms that make a clinical picture identical with 

 typhoid fever. It is more accurate therefore to look 

 upon the clinical condition of typhoid as being clue to 

 any one of a group of micro-organisms the chief 

 members of which are the typhoid, paratyphoid, and 

 paracolon bacilli, with forms intermediate between 

 each. 



