SULPHIDE PRODUCING ORGANISMS 
427 
Differentiation of Bacteria Isolated 
Glucose, lactose, saccharose, litmus milk and gelatine have mainly served for the 
differentiation of the organisms isolated. Mannite is generally fermented by those 
organisms which ferment glucose ; but in one or two instances it has been of some 
differential value. Glycerine has been of value in distinguishing coli from closely 
related forms. 
The media were constituted as follows : — glucose, -5 per cent, in two per cent, 
peptone water ; lactose, saccharose, mannite, and glycerine, each one per cent, in two 
per cent, peptone water. All these contained litmus as indicator of acid formation, and 
Durham tubes to aid in the detection of gas formation. 
The bacteria are not arranged according to relationship, but as before mentioned, 
according to power of sulphide production, so far as could be indicated by the 
rapidity and intensity of the blackening of media and lead paper, and the strength of 
odour evolved. Nos. 1-9 are very strong, 10-12 are strong in ten per cent, peptone, 
13-14 moderately so, and 1 5-21 are weak. The first nine are capable of blackening a 
favourable medium in twelve hours. 
It will be observed that several of the organisms form very little gas in saccharose. 
It might be suggested that the smallness of the amount is due merely to a variation 
in the fermenting power, and not to be regarded as a distinguishing feature of an 
organism. It can be stated, however, that during the months that these bacteria have 
been under observation, the amount of gas formed has never been greater. The 
weakness of the fermentation is also suggested by the absence of acid formation. 
Another constant and peculiar feature appears in No. 5, viz., rapid fermentation of 
lactose sugar, with formation of acid and gas, side by side with the marked acidifying 
of milk, without the formation of clot — even after two months incubation. Nos. 15 
and 21 are likewise to be distinguished by the more luxuriant growth, and the 
excessive bluish green fluorescence of the former on all forms of media. No. 21 
shows a very little fluorescence on some of the sugar media, and agar. No. 10 and 
No. 13 differ from each other in their growth on plates of MacConkev's taurocholate 
lactose agar ; ,; No. 13 presenting about its colonies the clear rings peculiar to 
Pfeiffer's bacillus capsulatus. No. 10 on the other hand forms colonies like bacillus 
coli of Escherich, and as it also ferments glycerine and saccharose, it is probably 
bacillus lactis aerogenes. No. 8 differs from the B. coli of Escherich in its decoloni- 
zation of saccharose and in its fermentation of glycerine. 
A number of other strong sulphide formers will be observed to be related to the 
coli group in their fermentation of sugars, e.g., 2, 3, 4, 5. 
No organism has been regarded as a form of coli that does not form acid and 
gas with lactose, and acidify and clot milk. 
In conclusion, I have to express my obligation to Professor Boyce, who 
proposed this work, and to whom I am indebted for many kind suggestions, also to 
my laboratory associates and Dr. Titherley for help given. 
