RUSSELL'S MEDIUM 319 
above methods for identifying members of the colon-typhoid group. 
Russell has deseribed the preparation and use of this medium in the fol- 
lowing manner: 
‘““ Enough 5 per cent aqueous solution of litmus (3 to 5 per cent) is 
added to plain agar (2 to 3 per cent) which usually has a reaction of 
about .8 per cent to phenolphthalein, to give it a distinct purple violet 
color, the amount of the litmus depending on the original’ color of the 
agar; dark requiring more than light, and the reaction then adjusted 
by adding sodium hydrate until the mixture is neutral to htmus. Next, 
and last, 1 per cent of lactose and 75 of 1 per cent of glucose dissolved in 
a small amount of hot water is added and the medium tubed for slants. 
The sterilization is done in the Arnold and, because of the danger of 
breaking down the lactose, must not be carried too far; if the tubes are 
packed loosely in the sterilizer basket to allow good circulation of steam, 
ten minutes on the first and fifteen on the second day has been time 
enough. The tubes are then slanted and stored in small quantities in 
a dark place. 
“On this double sugar tube, the typhoid bacillus gives, after an 
incubation period of from eight to eighteen hours, an extremely char- 
acteristic appearance; the surface growth is filiform and colorless, the 
upper part of the tube is unchanged in color but the lower part, the butt, 
is a brilliant uniform red. The entire point of the medium rests upon 
the difference in the changes produced by the growth of the typhoid 
bacillus under aerobic and under the imperfect anaerobic conditions 
found in the butt of the tube, where the bacillus obtains its oxygen by 
breaking down the glucose with the liberation of considerable acid; on 
the surface, however, in the presence of free oxygen, no acid is formed. 
‘The colon bacillus, which is often slow in producing acid on the 
Endo plate, shows abundant gas and acid formation on this medium. 
The tube is reddened throughout, both above and below, and since the 
abundant lactose is attacked equally with the glucose there is exuberant 
gas formation... . 
“The bacillus fecalis alkaligenes and other alkali formers leave 
the medium unchanged or slightly bluer. The staphylococcus reddens 
the tube above but leaves it blue below; the streptococcus intestinalis, 
when it grows well, gives a beaded growth and reddens the tube slightly 
throughout. B. subtelis, which is commonly found in feces, usually 
leaves the medium unchanged but may redden it below without pro- 
ducing gas, yet the heavy, rough surface growth suffices for its differ- 
entiation. B. pyocyaneus gives a greenish blue surface growth and leaves 
the color of the medium unchanged. 8B. proteus produces small gas bub- 
