ISOLATION OF BACILLUS TYPHOSUS 597 



teristic offshoots resembling a bone-corpuscle or the body of an 

 acarus. By using this 15 per cent, gelatin, which can be incubated 

 at 25 C., there is the double advantage of speedy growth and 

 formation of very characteristic colonies. 



Houston recommends S.D.S. rebipelagar (p. 592) with the addi- 

 tion of malachite -green to the extent of 1 in 5000 (0-2 grm. to the 

 litre). On this medium B. typhosus forms colourless colonies ; 

 most other bacteria do not grow, or appear as blue-black colonies. 



9. Werbitzlci's China green agar. For this 3 per cent, nutrient 

 agar (reaction +13) is used, and to every 100 c.c. of the agar 

 1-4-1-5 c.c. of a 0-2 per cent, aqueous solution of china green 

 (Griibler's) are added. 



10. Brilliant green agar. Conradi devised an agar containing 

 brilliant green and picric acid, and this has been modified by Fawcus * 

 as follows : To 900 c.c. of tap-water are added sodium taurocholate, 

 5 grm. ; powdered agar, 30 grm. ; peptone, 20 grm. ; and sodium 

 chloride, 5 grm. Dissolve the constituents by steaming for three 

 hours, filter through wool, and bring to a reaction of + 15 (by 

 means of lactic acid or NaOH, as the case may be). In 100 c.c. of 

 distilled water dissolve 10 grm. lactose and add this to the former 

 filter, distribute in flasks (100 c.c. in each), and sterilise. At time 

 of using, melt and add to each 100 c.c., 2 c.c. of a 1-1000 aqueous 

 solution of brilliant green and 2 c.c. of a 1-100 aqueous picric acid 

 (extra-pure, Griibler's). Typhoid forms round, transparent refrac- 

 tile colonies of a light pale green colour by transmitted light, B. colt 

 dark green colonies with an opaque spot at the centre. 



CONCLUSION. The writer would suggest for the isolation 

 of B. typhosus from water : (1) Concentration of the 

 organism by precipitation with alum (Willson's method) 

 or iron oxychloride, followed by plating of the precipitate 

 on Conradi-Drigalski agar, or, better, on malachite green 

 agar (Loffler's or Houston's, No. 8 above), or brilliant- 

 green agar (No. 10 above) ; (2) enrichment by Loffler's 

 method and subsequent plating. In all cases the organism 

 isolated must be examined as to its morphological, cultural, 

 and biological characters, and should have its agglutination 

 and Pfeiffer reactions tested with a high-grade typhoid 

 serum. Two organisms which are likely to be mistaken 



1 Journ. Roy. Army Med. Corps, February 1906, p. 147. 



