BNDO’S MEDIUM 53 
II. Preparation of the indicator. 
(a) Prepare a 10 per cent basic fuchsin solution in 96 per cent 
alcohol. This solution is fairly stable if kept away 
from the light. 
(b) Prepare a 10 per cent solution of chemically pure anhydrous 
sodium sulphite. (1 gm. in 10 c.c. water.) This solu- 
tion does not keep. 
(c) Add 1 c.c. of II(a) to 10 c.c. of II(b) and heat in the Arnold 
sterilizer for twenty minutes. The color of the solution 
should be nearly discharged. This solution must be 
prepared each day. It does not keep. 
IIJ. Preparation of medium. 
(a) Add 1 gm. of c.c. lactose to 100 c.c. of the agar and place 
in the autoclave until melted and lactose is dissolved. 
(b) Add enough of II(c) to impart a pink color (about I e.c.). 
(c) Pour into sterile Petri dishes and allow to harden. In the 
above medium Kendall has reduced the agar content 
to 1.5 per cent. The original formula of Endo called for 
a 3 per cent solution which was supposed to prevent 
diffusion of the acid and prodistinct colonies. 
Endo’s Medium (Hygienic Laboratory Method). Hasseltine (1918) 
has described the preparation of this medium as follows: It consists 
of a 3 per cent agar which is titrated and corrected to +0.5 to phenol- 
phthalein, to which is added 3.7 ¢.c. of a 10 per cent solution of anhy- 
drous sodium carbonate. For convenience it is flasked, sterilized and 
stored in 200 c.c. quantities. When ready to use the following ingredi- 
ents are added to 200 c.c. of agar as follows: 
(a) Dissolve 2 gms. chemically pure lactose in 25 to 30 c.c. of distilled 
water, with the aid of gentle heat. 
(b) Dissolve 0.5 gm. of anhydrous sodium sulphite in 10 to 15 c.c. 
of distilled water. 
(c) To the sulphite solution add 1 c.c. of saturated solution of basic 
fuchsin in 95 per cent alcohol. 
Add the fuchsin sulphite solution to the lactose solution and then 
add the whole to the agar. Pour plates at once, and after hardening 
dry for fifteen minutes in the incubator. 
Teague (1918) has shown that a 10 per cent solution of sodium 
sulphite may be heated for twenty minutes at 15 lbs. with practically 
