18 



fish and the water, and that by this method we were enabled 

 to determine the number of B. typhostis introduced into 

 the shellfish or into the surrounding water. 



Now, what are the characters by which the B. typhosus 

 can be readily recognised by the Drigalski-Conradi plate 

 method ? 



A given small amount of water or of substance of shell- 

 fish up to O'l c.c.* containing a limited number of B. 

 typhosus is uniformly rubbed, after the Drigalski method, 

 over the surface of the medium (Nutrose, litmus, lactose, 

 crystal violet, agar), previously set about quarter-inch 

 depth in a flat plate dish the plate dish which I use is 

 four-and-a-half inches in internal diameter and seven- eighths 

 of an inch deep and the plate is then placed in the incu- 

 bator at 37 C. 



Inspecting the plate after 24 hours, the typhoid colonies 

 are at once recognised as isolated round translucent blue dots ; 

 when inspected with a glass in semi-reflected light, they are 

 violet-blue, and well differentiated from the purple medium ; 

 the colonies are moist looking, thin at their margin, a little 

 thicker in the centre ; after 48 hours, and better still after 

 72 hours, the colonies are several millimetres in breadth, bluish 

 in the middle, violet at the thin margin, which latter at the 

 same time has lost its regularly circular outline, being slightly 

 irregular ; in transmitted light the substance is distinctly 

 but finely granular, and, owing to the prominent thicker 

 centre, the colonies look more or less Hke limpets, being low 

 conical. When a trace of the colony is distributed in a little 

 sterile bouillon, the bacilli which constitute the substance of 

 the colony are seen to be shorter or longer cylindrical rods, 

 many of them actively motile. When tested according to 

 Koch-Drigalski's method, by mixing a few drops of the bouillon 

 emulsion with a trace a small platinum loop of blood 

 serum of a typhoid-prepared animal, it will be seen that 

 arrest of motility and distinct agglutination into large 



* This amount can be easily spread out and rubbed over the plate 

 surface, without leaving any excess fluid even 0-15 c.c. can be so dealt 

 with ; more than that cannot be satisfactorily managed. 



