19 



compact clumps occur within a minute or two. As wo 

 shall point out later in detail, colonies may be blue or bluish 

 or blue-violet, without being those of B. typhosus, but the 

 above differential characters, viz., conical in shape, with 

 prominent centre, flat thin margin, violet-blue in the middle 

 part, violet in the margin when viewed in reflected light on 

 black ground, finely granular, moist or glistening in aspect ; 

 the individual bacilli short cylindrical in shape (not fila- 

 mentous and not in chains), motile and quickly clumping 

 and in marked manner with typhoid serum, are sufficient 

 presumptive indications * of the colonies beiog those of B. 

 typhosus. Subcultures in the different media are made as a 

 matter of routine, so as to confirm the diagnosis. 



We proceed now to describe in detail the experiments 

 which we made with oysters, cockles, and mussels. 



In all our experiments with oysters, the method used 

 was this : the oyster, after the outside of the shell had been 

 thoroughly washed and brushed under the tap, was opened 

 with a sterile knife, the liquor was drained off as completely 

 as possible, the body of the fish with its mantle and branchiae 

 was then transferred to a sterile glass dish and herein cut up 

 (minced) with sterile scissors as finely as possible; after 

 thoroughly mixing the minced material, the fluid (thick 

 turbid) is removed with sterile glass pipette and measured. 

 From this fluid a definite amount, in no case more than 

 O'l c.c. or 0*15 c.c. (generally the former quantity), was 

 either directly transferred to a Drigalski plate, or, as in those 

 cases in which the presence of a large number of B. typhosus 

 in the oysters could be supposed, -fa c.c. of the oyster-mince 

 was first diluted by a measured amount of sterile sea water, 

 and of this dilution -fa c.c. was used and dealt with on 

 the Drigalski medium in the plate. If the number of 



* Flat colonies, deep blue in reflected light, fringed at margin, dry 

 looking, are not B. typhosus; colonies bluish or pale blue in reflected 

 light, with greenish margin, uniformly raised, moist looking, are not B. 

 typhosus ; colonies bluish violet, strongly granular, with thin margin, but 

 composed of filamentous bacilli, are not B. typhosus, they do not grow on 

 Drigalski plate at 37 C. Very small, blue, uniformly-raised, colonies may 

 be those of streptococci or vibrios. 



c 2 



