MEDIA FOR SEPARATING BACTERIAL GROUPS 49 



Conradi's Picric Acid Brilliant Green Method. Applying his principle 

 of seeking for anilin bodies which while inhibiting the action of ordinary 

 intestinal bacteria rather favour the growth of b. typhosus and b. para- 

 typhosus, Conrad i in 1908 used for this purpose crystalline brilliant 

 green (Hoechst, extra pure), acting along with picric acid (Griibler). The 

 medium is made as follows : 900 c.c. water, 20 grins. Liebig's meat extract 

 and 100 c.c. of a 10 per cent, watery solution of Witte's peptone are 

 mixed and filtered ; 30 grms. agar in threads are dissolved in the Huid, and 

 the whole filtered. The reaction is then adjusted with normal sodium 

 hydrate or normal phosphoric acid to an acid content of 3 per cent, 

 (phenol-phthaleine being the indicator), i.e. the finished medium is 

 such that to make it neutral would require the addition to each 100 

 c.c. of 3 c.c. of normal sodium hydrate. The acid medium is then 

 sterilised, and kept in bulk in this form. For use the remaining 

 substances are added in the proportions of 10 c.c. of 1-1000 watery 

 solution of the brilliant green and 10 c.c. of 1 per cent, watery picric 

 acid to 1^ litres of the peptone-agar, and the finished medium is poured 

 in large Petris and allowed to stand at 37 C. till the surface is firm. 

 The capsules are inoculated in the waj r already described. Typhoid 

 colonies appear sharp-edged, round, flat-surfaced but slightly thicker 

 in the middle, transparent, and of light green colour. Colonies of the 

 paratyphoid bacillus are similar, but tend at the same age to be slightly 

 larger and have a somewhat yellowish green tint. 



Fawcus's Picric Acid and Brilliant Green Medium. This is a 



modification of Conradi's medium which has been used with great 

 success at the Royal Army Medical College in the investigation of 

 typhoid carriers. It is made as follows : To 900 c.c. tap water add 

 5 grms. sodium taurocholate (which is commercially prepared from ox 

 bile), 30 grms. powdered agar, 30 grms. Witte's peptone, 5 grms. sodium 

 chloride ; steam for three hours, clear with white of egg, filter through 

 cotton wool, and bring to a reaction of + 15 with normal lactic acid or 

 caustic soda, and sterilise. Dissolve 10 grms. lactose in 100 c.c. sterile 

 distilled water, and add to melted agar. Mix and filter through Chardin 

 paper, sterilise carefully, and store in 100 c.c. flasks. For use, add to 

 each 100 c.c. flask 2 c.c. of a 1-1000 watery solution of brilliant green 

 and '2 c.c. of a 1 per cent, watery solution of picric acid. Pour into 

 large Petri dishes, and leave these to stand inverted at 37 C. till the 

 surface hardens. Inoculate as usual. Colonies of b. typhosus of twenty- 

 four hours' growth are of about 1 mm. in diameter, transparent and re- 

 fracting - those of b. coli, on the other hand, have a deep green centre, 

 though later typhoid colonies may also present a pale green centre. 



In the case of several of the special media used for the isolation of 

 typhoid bacilli under circumstances where other bacteria are present, a 

 difficulty arises from the fact that the agglutinability of the strains 

 isolated appears to be affected by substances present in the media. 

 The application of this important confirmatory diagnostic method is thus 

 interfered with. This is said not to occur with the Conradi brilliant 

 given method, and we have found with this medium that, if typhoid 

 colonies do not at once clump with typhoid serum, daily sub-culture on 

 ordinary agar yields in a few days a culture to which the agglutination 

 test can be applied. 



Endo's Medium. This is another of the modern media introduced for 

 facilitating the separation of the b. typhosus from stools, etc. It is 

 made as follows: A litre of 3 per cent, agar is prepared with the usual 



