Bacilli Resembling the Typhoid Bacillus 653 



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 

 distributed 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 ioo°C.) . 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 yeUow. 



Castellani* recommends the following method to facilitate the 

 i'solation of the bacilli of the typhoid-paratyphoid groups : 



I. Inoculate with the fecal matter to be investigated several tubes of tauro- 

 cholate of soda peptone water, or Browning, Gilmore and Mackie's telluric acid 

 peptone water might be used. 



1. Immediately after, or better immediately before, the inoculation, add S 

 drops of polyvalent lactose fermented intestinal bacteria serum (B. proteus 

 group, etc.), taking care to use serums containing only a very small amount of 

 typhoid coagglutinin; or serum can be used from which the typhoid coagglutinin 

 has been removed by absorption. 



3. Incubate for twelve or twenty-four hours, then make plates on MacConkey, 

 Conradi-Drigalsky or similar media, from the most superficial portion of the 

 liquid medium, and further investigate any suspicious colonies that may develop 

 with typhoid, paratyphoid A and paratyphoid B serums, etc. When there are 

 many flocculi of agglutinated bacilli also in the upper part of the tube, these 

 may be got rid of by a short centrifugation with an ordinary electric centrifuge 

 which causes the agglutinated bacilli to fall to the bottom, while it has practi- 

 cally no effect upon the non-agglutinated organisms in young cultures. 



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, saccha- 

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



H 2 

 m the proportion of ^^ = -• 



Between these extremes are numerous organisms known as "inter- 

 mediates." It is usually a simple matter to differentiate these forms 

 from the t3^ical 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 

 *Brit. Med. Jour., 1917, n, P- 477. 



