APPENDIX 167 



agar add 2 c.c. of a O'l per cent, watery solution of brilliant 

 green (extra pure) and 2 c.c. of a ro per cent, watery solution of 

 picric acid. The resulting clear bright green agar is poured 

 without further heating into Petri-dishes. After solidification 

 the plates are dried uncovered and upside down in the 

 incubator and after two to three hours are ready for use. The 

 medium should not be kept in flasks ready made. The most 

 convenient plan is to distribute the bile-salt lactose agar into 

 flasks about 150 c.c. into each. When required for use one 

 of these is melted and 3 c.c. of each of the solutions of the 

 brilliant green and the picric acid added and well mixed. The 

 finished agar contains O'$ per cent, bile-salt, I in 50,000 brilliant 

 green and I in 5000 picric acid. 



Colonies of B. typhosus and Gaertner group bacilli are round 

 and quite transparent. B. coli colonies have a dark green 

 opaque spot in the centre. 



Neutral Red Lactose Bile Salt Agar (L.B.A.}. Sodium 

 taurocholate 5 grammes, Witte's peptone 20 grammes, and 

 distilled water I litre, are boiled up together, 20 grammes of agar 

 are added and dissolved in the solution in the autoclave in the 

 ordinary way. The medium is cleared with white of egg and 

 filtered. After filtration, 10 grammes of lactose and 5 c.c. of 

 recently prepared one per cent, neutral red solution are added. 

 The medium is then tubed and sterilized for 15 minutes on three 

 successive days. 



L.B.A. Crystal Violet. Some workers use L.B.A. to which is 

 added crystal violet (i in 100,000). The crystal violet acts also 

 as an inhibiting agent. 



Fuchsin Agar. Introduced by Endo. The following modified 

 method of preparation has been found by the writer more satis- 

 factory and uniform than the original : 



Peptone, 10 grammes ; Liebig's extract of beef, 10 grammes ; 

 sodium chloride, 5 grammes, are boiled up in an enamelled 

 dish with i litre of distilled water. The mixture is then poured 

 into a flask, 30 grammes of powdered agar added, and the whole 

 heated in the autoclave at 115 C. for one hour. The flask 

 is removed, and, after cooling to about 60 C., the white of one 



