THE TYPHOID BACILLUS 



281 



then inoculated with a loop of urine or much diluted feces. In this 

 way we are apt to have some plates with just the right amount of 

 colonies. 



Appearance of the Colonies. Capaldi thus describes the differentia- 

 tion : Typhoid Small, glistening, transparent, almost colorless colonies 

 (by reflected light, blue). Colon Large, milky colonies (reflected 

 light, brown). 



In using the medium it was found that even in a pure plate of typhoid 

 the colonies vary much in size and appearance, while different typhoids 

 show individual differences in growth. In general, a medium-sized, 

 gray-white colony, with a few refractive granules, is the typhoid. 

 However, it is often transparent, without the refractive granules; 

 sometimes with a nuclear centre, and sometimes of equal consistency 

 throughout. Streptococci simulate typhoid, but a high-power lens will 

 show the coccus. 



Colon colonies are usually much larger than the typhoid a decided 

 brown color, very large, refractive granules, and in general quite dif- 

 ferent in appearance (Fig. 95). 



FIG. 95 



Colonies of colon bacilli on Capaldi medium slightly magnified. Typhoid colonies of same 

 size usually have no dark granules. 



The best way to work with the Capaldi medium is to make several 

 plates with different typhoid cultures, observe carefully all the varia- 

 tions in the colonies, and bear these in mind when working with the 

 mixed plates. After these precautions have been taken the medium 

 will be found very satisfactory. The colonies, as a rule, appear char- 

 acteristically in twelve to eighteen hours, and thus give a quick method 

 of diagnosis. 



We found that the two media (Capaldi and Hiss) work excellently 

 together, as one is an aid to the other. When many colonies of the 

 typhoid bacilli were present the points of differentiation were usually 



