BACILLUS TYPHOSUS. 439 
medium will be found very satisfactory. The colonies, 
as a rule, appear characteristically in twelve to eigh- 
teen hours, and thus give a quick method of diagnosis. 
The two media together (Capaldi and Elsner) work 
excellently, as one is an aid to the other. When 
many colonies of the typhoid bacilli were present the 
Fig. 57. 
Colonies of colon bacilli. Capaldi medium slightly magnified. 
differentiation was usually easily seen upon both media, 
and the two together made diagnosis almost certain. 
The bacilli from the suspected typhoid colonies can be 
quickly tested sufficiently for practical purposes on the 
Hiss tube medium and by the reaction between the 
bacilli and the serum from an immunized horse. 
As to the comparative merits of these three media, 
it is probably safe to say that any one of them will, in 
the hands of one accustomed to them, reveal the typhoid 
bacilli, if they are present, except perhaps when they 
