722 A MANUAL OF BACTERIOLOGY 



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. Browning, Gilmour and 

 Mackie's method might also be employed (p. 441). 



Houston recommends S.D.S. rebipelagar (p. 717) with the 

 addition of malachite -green to the extent of 1 in 5,000 (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. 



Werbitzki used china green cigar ; 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. 



Conradi devised an agar containing brilliant green and picric 

 acid, and this has been modified by Fawcus l 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 1-1,000 aqueous 

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

 (extra-pure, Griibler's). B. typhosus forms round, transparent 

 refractile colonies of a light pale green colour by transmitted light, 

 B. coli dark green colonies with an opaque spot at the centre. 



Houston found malachite green agar a better medium for the 

 isolation of the typhoid bacillus than a liquid brilliant green fluid 

 medium (see p. 441). 



CONCLUSION. The writer would suggest for the isola- 

 tion 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), or brilliant green agar ; 

 (2) enrichment by Loffler's or by Browning, Gilmour 



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



