400 
THOMPSON YATES LABORATORIES REPORT 
The characteristic decolourization was not seen in fluid glucose media. It was 
strikingly brought out, however, that Neutral-red lactose peptone water would differ- 
entiate B. coli from the other groups far more sharply than Neutral-red glucose media. 
In such a medium the cultures of B coli changed the Neutral-red colour to cherry-red. 
(A similar change of colour was observed on the addition of one drop of acid, mineral 
or organic). For purposes or comparative study this medium proved fully as satis- 
factory as PetruschkyV 0 Neutral litmus whey ; its constitution is certainly more 
constant than that ot the latter medium. Merely as a qualitative medium, Neutral- 
red may be more useful than litmus in the study of these particular groups, because 
of the frequent decolourization of the latter ; but for rapid differential work Neutral- 
red can hardly be considered a valuable adjunct, especially as used by those who have 
recommended it hitherto ; glucose agar will differentiate the groups as well without 
the addition of Neutral-red as with it. 
Lactose litmus agar. First synthesized by Wurtz, 45 and modified later by 
Kashida, 20 this medium has been very recently brought into prominence by von 
Drigalski and Conradi, 6 who have succeeded by its use in isolating B. typhosus from 
the stools of each of fifty typhoid patients examined, as well as from the stools of 
several individuals, attendants in typhoid wards, who had shown no symptoms of 
illness. 
Neutral litmus ivhe\. At Durham's 9 suggestion the whey was neutralized, not 
with HQ, but with 4 per cent, citric acid solution. After six weeks growth at 37°C, 
the reactions, estimated quantitatively, were as follows : — 
B. typhosus : acid (= o - 5 per cent, normal KOH). 
B. enteritidis : alkaline (= 4-25 ,, ,, HC1). 
Bacillus ' L ': acid (=3-25 „ „ KOH). 
B. coli : acid (= fro „ „ KOH). 
Fermentation reactions in sugar media. This method gave very constant results. 
To avoid irregularity of constitution, simple peptone-water media were used in each 
case, the formulae being those recommended by MacConkey and Hill. 27 Durham's 7 
fermentation tubes proved very satisfactory for preliminary determinations as to gas 
production ; all the results were checked later by the use of Theobald Smith's 57 fer- 
mentation tubes, incubation lasting seven days. Determinations at the end of this 
time showed that Bacillus 'L' corresponded very closely with B. enteritidis in its 
fermentative powers. The nature of these fermentative changes in sugar media has 
been recently carefully studied by Harden. 16 
Formation of Indol. Kruse 22 pointed out in 1894 that the presence of 0-25 per 
cent, of glucose in bouillon inhibited indol-production. Theobald Smith, 5? later on, 
showed that a medium entirely sugar-free gave the most reliable results. The tests 
were made, therefore, according to the method outlined by him. A series of tubes of 
