GENERAL BACTERIOLOGY 
109 
On such a medium the typhoid colonies are colorless, 
while those of colon bacilli are red. 
13. Russell's Double Sugar Medium 
Russell’s double sugar medium is used for the differen¬ 
tiation of the typhoid, paratyphoid and colon bacilli. 
(a) Prepare ordinary meat extract agar (25 grams 
of agar per 1,000 c. c. of medium, 0.8 per cent acid) and 
keep it in flasks. When needed, melt it. 
(b) Add enough of sterile 5 per cent aqueous solu¬ 
tion of litmus (usually about 30 c.c.) to give the medium 
a distinct violet color. 
(c) Add 0.1 per cent glucose (grape sugar) and 1 per 
cent lactose (milk sugar) dissolved in 50 c.c. of water, 
tube and sterilize in Arnold’s sterilizer for fifteen min¬ 
utes on three successive days. Slant. When inoculations 
are made smear the surface and also stab. 
On such a medium typhoid growth will show a par¬ 
tial red color formation and no gas bubbles. The para¬ 
typhoid A and B will show a partial red color formation 
and gas bubbles in the red area, while the colon growth 
will turn the entire tube red and gas bubbles all over. 
14. The Double Sugar—Lead Acetate—China Blue 
Medium 
This medium is the most complete differentiating me¬ 
dium, as it tells at a glance whether the growth is one of 
typhoid, paratyphoid A, paratyphoid B, colon or B. en- 
teritidis. 
(a) Prepare ordinary meat extract agar, 0.3 per cent 
acid, and flask it. 
(b) Heat some 2 per cent neutral lead acetate in sterile 
distilled water, at 100° C. for one hour in water-bath, 
5 c.c. of this is added to 100 c.c. of agar (which has been 
