406 TYPHOID FEVER 



from the intestine of newly-born infants in connection with the 

 first appearance of bacteria in the alimentary tract. About the 

 same time, an organism now known as the bacillus neapolitanus 

 was obtained by Emmerich in an outbreak of choleraic disease 

 in Naples, and this organism was looked upon as identical with 

 Escherich's bacillus, but it ferments saccharose, on which 

 Escherich's has no effect. The bacillus acidi lactici of Hiippe 

 was stated by this observer to be the chief cause of the souring 

 of milk. It is now known that a large number of organisms of 

 the same type, but differing slightly in cultural characters, are 

 concerned in this process, and, as a matter of fact, MacConkey 

 found the presence of the classical strain to be relatively infre- 

 quent in milk. The bacillus lactis aerogenes was originally 

 described by Escherich, in connection with his work on the 

 bacteriology of the intestine in children, as an organism differing 

 from the ordinary milk-souring bacteria by its producing gas 

 from milk in the absence of air. Although it is a free gas- 

 producer, this property is not specific for it, and within recent 

 years it has attracted attention chiefly from its apparently being 

 closely allied to the bacillus pneumoniae of Friedlander. Like 

 the latter, this organism is stategl when injected into animals to 

 appear in a capsulated form. Another member of this group is 

 bacillus oxytocus perniciosus, which is said originally to have 

 been isolated from milk. This organism, along with the bacillus 

 vesiculosus and an organism denominated No. 71, were found 

 by MacConkey to be of^very common occurrence in human and 

 animal faeces. 



In work of the kind with which we are dealing, two other 

 organisms are not infrequently observed which morphologically 

 belong to the coli-typhoid group, but neither of which is a 

 lactose fermenter. These are the bacillus fsecalis alcaligenes, 

 and the bacillus coli anaerogenes. The reactions of these will be 

 found in the Table opposite. The latter bacillus somewhat 

 resembles the typhoid bacillus, but produces acid in lactose 

 and can be distinguished by agglutinating reactions. 



When any question arises regarding the relationships of an 

 organism isolated under saphrophytic conditions and resembling 

 some definite pathogenic type, important information can often 

 be obtained by studying its agglutinating reactions. In such a 

 case the effect of sera produced by the pathogenic type upon 

 the unknown organism, and of sera produced by injection 

 into animals of the pathogenic type in question, ought to be 

 studied. 



The Question of Mutation. It is becoming more and more 



