SULPHIDE PRODUCING ORGANISMS 
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Nature of the Sulphur Compounds 
It would be most difficult to determine what combinations of the sulphur are 
effected by the bacteria from the various sulphur-containing bodies. It is clear that 
the blackening of the media does not indicate necessarily the formation of sulphide of 
hydrogen. It means simply that the sulphur is liberated in the free state or in com- 
bination with some element or radicle, double decomposition occurring thereafter with 
the formation of the black sulphide. There is no doubt, however, that sulphide of 
hydrogen is the preponderating compound formed. This is evidenced by its powerful 
odour, and the rapid blackening of the lead paper. After one or two days it may be 
evolved in such quantity by several of the bacteria that the medium is densely black, 
and the gas passing off in such quantities as to be detected by its odour throughout 
a large room. Lead paper held over the openings of the tubes is instantly blackened. 
A single stab of No. 1 in ten per cent, ferro-peptone agar caused, in thirty-six hours, 
such excessive gas formation that the densely black medium was split apart and driven 
upwards in the tube. 
The odour of sulphide of hydrogen is always mingled with a number of other very 
disagreeable odours. Among these may be distinctly detected the sharp penetrating 
odour of mustard oils. 
Mercaptans were detected after several days' incubation by their reaction with 
isatine. A drop of one-quarter per cent, solution of isatine in concentrated sulphuric 
acid, deposited in the necks of tubes inoculated with organisms No. 1 and No. 5, 
was changed in several minutes, or even less, from a yellowish red to a deep clear 
green. With several of the other active forms a reaction was less definite ; the 
yellowish red colour disappeared and was succeeded by a faint faded green. 
One form (No. 15) caused some darkening of the iron-containing media, but 
never was observed to blacken the lead paper, whether iron were present or not. 
The sulphide here cannot be sulphide of hydrogen. It must be of non-volatile 
character. 
The remaining bacteria caused blackening of the lead paper too quickly to be 
accounted for without hydrogen sulphide. In every instance there was also some 
black deposit in the bottom of the tubes of media. 
Method of Formation of Sulphide of Hydrogen 
It has been widely accepted, 6 ' + ' s ' that the formation of sulphide of hydrogen 
by bacteria is due to the action of nascent hydrogen, evolved through the activity of 
the bacteria, upon free sulphur or its compounds, organic or inorganic. 
Debraye and Legrain s found that a number of bacteria fermenting maltose, 
with the formation of hydrogen, were capable of forming hydrogen sulphide when 
