DIFFERENTIATING TYPHOID BACILLI 21 



creasing the amount of the upper layer and slanting it, a streak 

 culture can be made before stabbing, as in the case of the Rus- 

 sell medium, and material will thus be available for agglutina- 

 tion tests without further transplantation. The medium is 

 readily prepared, and is inexpensive. It has been preserved for 

 one month in the ice-box without deterioration; by adding two 

 drops of sterile liquid paraffine to prevent evaporation, it can 

 probably be kept indefinitely. 



I next attempted to prepare a medium that would differen- 

 tiate between B. paratyphosus B and B. enteritidis, as well as 

 between these organisms and B. paratyphosus A, B. typhosus, 

 and B coli. The following represents the best combination 

 obtained for this purpose. Sugar-free agar is used for both the 

 lead acetate and the china blue; 1 per cent lactose, 1 per cent 

 inosite, and 0.1 per cent arabinose are added to the china blue 

 agar. With this medium the lead acetate layer behaves toward 

 the different organisms as in the preceding medium, and all of 

 the organisms produce gas in it, except B. typhosus. The shade 

 of blue produced in the upper layer after twenty-four hours' 

 incubation may be indicated as follows: 



B. typhosus + 



B. paratyphosus A + 



B. paratyphosus B. sub. 1 -\ — 1- 



B. paratyphosus B. sub. 2 — or trace 



B. enteritidis — or trace 



B. coli + + + 



B. paratyphosus B has been divided into two groups by Weiss, 

 according to whether the organism does or does not ferment 

 inosite; most of the strains ferment inosite, and so fall into his 

 sub 1 group. Therefore, the medium just described differen- 

 tiates sharply between most paratyphoid B strains and B. enter- 

 itidis but not between paratyphoid B sub 2 and B. enteritidis. 

 Fourteen of our paratyphoid B. strains belong to the sub 1 group, 

 and only five to the sub 2 group. The medium differentiates 

 quite sharply, — B. enteritidis and B. paratyphosus sub 2 remain- 

 ing colorless or producing a mere trace of blue; B. typhosus 

 and B. paratyphosus B showing pale blue; B. paratyphosus B 



THE JOURNAL OP BACrERIOLOGY, VOL. Ill, NO. 1 



