250 Prof. M. C. Potter. Bacteria as [Jan. 18, 
ment of any rise of temperature was a better means for testing oxidation 
than the collection and determination of the carbonic anhydride. 
The thermopile was therefore relied upon in order to determine whether 
coal sterilised by discontinuous boiling gives out any heat, and whether any 
thermal changes occur consequent upon the addition of bacteria. Small 
fragments of coal obtained as described were placed in a flask and immersed 
in distilled water, the aperture being covered with a small beaker, as cotton 
wool was inadmissible as a plug. The flask was steamed for five hours on 
two consecutive days, and on the third day the excess of water was partially 
driven off by boiling. The coal so treated was then introduced into a 
sterilised double-walled vacuum-flask, and placed in the incubator, a 
thermopile was inserted as before, and the connections made with the 
galvanometer according to the method previously recounted for charcoal. 
Immediately after setting up the apparatus, the thermopile indicated a 
temperature of the coal considerably above that of the incubator, this being 
due to its retaining some heat after boiling; but after 26 hours the research- 
flask had cooled down to the temperature of the incubator. Following this 
interval, the temperature of the coal gradually descended, which may be 
explained by the evaporation continuously taking place from the damp 
fragments of coal. Then for some three days it remained at 0°2 below 
that of the incubator, and it was quite clear that the coal thus sterilised 
generated no heat. 
This point being determined, the coal was inoculated with bacteria by 
pouring in distilled water containing these organisms, care being taken that 
the temperature of this added water was below that of the research-flask. 
The reduction of temperature was at once indicated by the thermopile, the 
spot of hght moving off the galvanometric scale in the direction opposite to 
the movement when the warm coal was first put in. Twenty-four hours 
after inoculation the temperature of the research-flask had not only risen to 
that of the incubator, but it had increased to 0°08 C. above it, and afterwards 
a marked rise of temperature amounting to 0°18 C. was steadily registered 
for 11 days. 
In the experiment just described, one terminal of the thermopile was 
inserted in the research-flask, and the other in a glass jar packed with cotton 
wool placed in the incubator, and in this manner any difference of tempera- 
ture between the research-flask and the incubator could be measured. But 
the experiment would not be complete without a control, and a second double- 
walled vacuum-flask, containing fragments of coal from the same source and 
treated in a precisely similar manner, was also placed in the incubator with 
a second thermopile, one terminal in each flask. The coal, however, in this 
