CHAPTER III. 

 BACILLI RESEMBLING THE TYPHOID BACILLUS, 



BACILLUS typhosus is one of a group of organisms pos- 

 sessing a considerable number of common characteristics, 

 each member of which, however, can be differentiated by 

 some one fairly well-marked peculiarity. At one end of 

 the series is the typhoid bacillus, of which we conceive as 

 devoid of the power to ferment sugars, form indol, coagulate 

 milk, or progressively form acids. At the other extreme 

 stands Bacillus coli communis, an organism whose typical 

 representatives coagulate milk, form indol, ferment dextrose, 

 lactose, saccharose, and maltose with the formation of hydro- 

 gen and carbon dioxid in the proportion of ^ = \. 



Between these extremes are numerous organisms known 

 as "intermediates." It is usually a simple matter to dif- 

 ferentiate these forms from the typical species at the two 

 ends of the series, but it is quite difficult to differentiate 

 them from one another. Whether they are of sufficient 

 importance to make it worth while to pay much attention 

 to them is, as yet, uncertain ; and, indeed, we do not know 

 whether they are to be regarded as variations from the 

 type species or separate and distinct organisms. The fact 

 that some of them are associated with serious and fatal 

 disorders paracolon and psittacosis suggests that they 

 have an importance that is just becoming recognized. 



In his careful review of the intermediate forms thus far 

 described, Buxton * summarizes the main points of difference 

 as follows : 



B. COLI INTER- B. TY- 



COMMUNIS. MEDIATES. PHOSUS. 



Coagulation of milk 



Production of indol -j- 



Fermentation of lactose with gas + 



Fermentation of glucose with gas + + 



Agglutination by typhoid serum + 



* "Journal of Medical Research," vol vm, No. 1, June, 1902, 

 p. 201. 



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