132 DR. A. J. EWART ON THE EVOLUTION OF 
4° C. a fairly active evolution of oxygen is shown, which after 
5 hours is still present but weak. Preparations kept at 4° C. 
which have just ceased to evolve oxygen may, on being brought 
to 20° C. in light or in darkness, or on a hot water-bottle being 
placed before the mirror, again show a weak evolution of oxygen 
continuing for a short time. At 4? C. the dark radiant heat-rays 
exercise a distinct accelerating effect upon the evolution of 
oxygen, causing it to be for a time more active but also to be of 
shorter duration. 
Altogether the foregoing results form a conclusive proof that 
the oxygen evolved is not the product of any assimilatory process 
involving an absorption of radiant kinetie energy and the con- 
version of this into potential ehemical energy. Two other 
explanations of the phenomenon alone remain, namely, that 
either the oxygen evolved is a by-product of some unknown 
katabolie process induced by the bacterium in the nourishing 
medium or taking place in its own plasma; or that the oxygen is 
simply absorbed oxygen taken from the air and held in a state 
of loose combination and at a lower partial pressure than that of 
the atmosphere being slowly given off again. 
The fact that at 4° C. the evolution of oxygen continues fairly 
actively, although at this temperature none of the coloured 
Bacteria mentioned can grow or multiply, and the fact that the 
Bacteria taken from agar-cultures 2-3 months old, in which by 
far the greater number of the Bacteria must be dead, may show 
a quite active evolution of oxygen on examination, form almost 
conclusive objections to the first hypothesis. Conclusive proof 
that the phenomenon is not connected with the vitality of the 
bacterium itself is given by the fact that old cultures, or cultures 
kept for many hours over ether-vapour, or cultures heated to 
80° C. for an kour, from which on re-inoculation no new growth 
takes place may show on examination an active evolution of 
oxygen, though frequently weaker than normal *. Thus agar 
cultures of Bacillus brunneus, Micrococcus agilis, Sarcina auran- 
tiaca, killed by heating to 80° C. for 1i hours, showed after ? 
* If the Bacteria are heated to 60? C. or 70? C. or exposed to ether-vapou 
for a time, but not long enough to kill them entirely, or inoculating in fresh 
agar-tubes, a slight and very slow growth may take place and the pigment ¥ 
formed as usual, though not abundantly. The colonies, however, soon cease to 
grow, and now, as a general rule, on re-inoculating in fresh tubes no new growth 
takes place, The vegetative vigour has been so weakened that the powe" of 
growth is finally completely lost. 
