Bacilli Resembling the Typhoid Bacillus 613 



from this stock solution by adding glucose, 0.5 per cent.; lactose, i per cent.; 

 cane-sugar, i per cent.; dulcit, 0.5 per cent.; adonit, 0.5 per cent., or inulin, i 

 per cent.; and neutral red (i per cent, solution), 0.25 per cent., distributing into 

 fermentation-tubes and sterilizing in the steamer for fifteen minutes on each of 

 three successive days. 



Bile-salt agar-agar is made by dissolving 2 per cent, of agar-agar in the stock 

 fluid, either in the steamer or in the autoclave. The mixture is cleared with an 

 egg, filtered, neutral red added in the same proportion as for the broth, and dis- 

 tributed into flasks in quantities of 80 cc. When required for use, the fer- 

 mentable substance is added to the agar in the flask, and the whole placed in a 

 water-bath or steamer (care must be taken not to heat either the fluid or solid 

 medium beyond iooC.). When melted, the agar preparation is poured into 

 Petri dishes, allowed to solidify, and then dried in an incubator or warm room, 

 the plate being placed upside down with the bottom detached and propped up 

 on the edge of the cover. It is necessary that the surface of the agar-agar should 

 not be too wet, lest the colonies become confluent, nor too dry, lest the growth 

 be stunted. Inoculations are made by placing a loopful of the material to be 

 examined on the center of one plate, and rubbed over the surface with a bent 

 glass rod; the same rod, without recharging, being used to inoculate the surface 

 of two other plates. The plates are then incubated upside down. The colonies 

 of the colon bacillus appear yellow. 



BACILLI RESEMBLING THE TYPHOID BACILLUS 



Bacillus typhosus is one of a group of organisms possessing a con- 

 siderable number of common characteristics, each member of which, 

 however, can be differentiated by some one fairly well-marked pecu- 

 liarity. At one end of the series is the typhoid bacillus, which we 

 conceive to be devoid of the power to liquefy gelatin, ferment sugars, 

 form indol, coagulate milk, or progressively form acids. At the other 

 extreme stands Bacillus coli, an organism whose typical representa- 

 tives coagulate milk, form indol, ferment dextrose, lactose, sacchar- 

 ose, and maltose with the formation of hydrogen and carbon dioxid 



in the proportion of =^~ = 

 CO 2 i 



Between these extremes are numerous organisms known as " inter- 

 mediates." It is usually a simple matter to differentiate 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 atten- 

 tion 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 bacillus and 

 bacillus of psittacosis proves them, at least, to be important. 

 Buxton* summarizes the main points of difference as follows: 



B. coli com- 

 munis. Intermediates. B. typhosus 



Coagulation of milk. -j- 



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. i, June, 1902, p. 201. 



