420 
THOMPSON YATES LABORATORIES REPORT 
great to be accounted for in this way. Concentration of meat extract does 
not cause increase of sulphide formation ; two per cent, and ten per cent. Liebig's 
extract are alike unfavourable media. Perhaps this may be due to an extent to a 
deficiency of sulphur in the extract. 
Flowers of sulphur in minute quantity, added to two per cent, peptone, clearly 
contributes to the amount of sulphide formed. This is quite equal to the amount 
foi -med in five per cent, peptone, although very much less than in ten per cent. 
The addition of sodium thiosulphate makes little difference. Sodium sulphite, 
except in very minute quantity, inhibits sulphide formation. 
Glucose added to the medium renders it more favourable for production of hydrogen 
sulphide by most of the tabulated organisms. This was determined as follows : — 
To a part of a solution of two per cent, peptone, containing T c.cm. tartrate of iron 
per litre, was added a minute quantity of flowers of sulphur ; to a second part, the same 
amount of sulphur and one-half per cent, glucose, with a quantity of calcium carbonate 
to neutralize acid formed ; the remainder was left unaltered. Each of these three media 
was inoculated as usual in tubes with the various organisms, lead paper being intro- 
duced, and incubated at 37 0 C. New sterile lead papers were introduced from day 
to day. 
Jt was observed that the medium containing the glucose was generally less 
darkened by the sulphide formed, at least by the more active organisms, than the non- 
glucose containing media. But on the other hand the amount of hydrogen sulphide 
escaping from the tubes was with some organisms much greater with the glucose 
containing medium ; for the lead papers introduced from day to day immediately 
became black in these instances, whereas this did not occur with the non-glucose 
containing media. 
The less degree of blackness in the glucose media was probably due to the fact 
that the insoluble calcium carbonate in the bottom of the tubes did not sufficiently 
neutralize the medium to permit of the ready deposit of the sulphide of iron. 
Organism No. 12 (see table appended) affords one of the best illustrations of the 
favouring action of glucose. In two per cent, peptone with or without free sulphur its 
powers of hydrogen sulphide formation are very slight. After seven days incubation 
the liquid of these media was scarcely at all darkened, the main evidence of sulphide 
formation being a slight black deposit in the bottom of the tubes, and a very moderate 
blackening of the lead papers. But in the glucose medium all of the fluid soon darkened, 
and each lead paper introduced from day to day blackened immediately. That intro- 
duced on the seventh day became blacker in a few minutes than any of those which 
had been suspended for days over the non-glucose containing media. Nos. 8, 10, 1 1, 
13, also show very marked increase in glucose medium. 
Such increase continues only so long as calcium carbonate remains in the tube. 
With its exhaustion the fluid loses what blackness it possessed, and new lead papers 
