128 DR. A. J. EWART ON THE EVOLUTION OF 
movement, even though a small drop containing only a hundred 
or two of Bacteriwm Termo is used, from which no appreciable 
trace of CO, is evolved. 
It appeared at first as if the coloured Bacteria evolved oxygen 
more rapidly in an atmosphere of H containing a little CO, 
than in an atmosphere of pure H. The experiments were 
performed in the following manner :—The time which it takes for 
the B. Termo which have been brought to rest by a current of 
H to recommence to move, when the tubes leading to and from 
the chamber containing the coloured Baeteria are clamped, is 
determined. Then a mixture of H and CO, is passed through 
the chamber, when, on closing, the B. Termo recommence to 
move in a shorter time than they did alone. Further examination 
showed, however, that this difference was due to the presence of 
traces of oxygen in the CO, employed. To remove this oxygen 
the CO, was passed over tubes of pyrogallol and KHO. Theo- 
retically, owing to the absorption of the CO, by the potash, this 
arrangement should be unworkable, but practically it was found 
possible to obtain CO, in this manner perfectly free from all 
traces of oxygen. The evolution of oxygen can now be demon- 
strated to take place with equal rapidity in an atmosphere of H 
alone, as in one composed of H with a little CO,. 
A possibility not as yet excluded is, however, that a process 
of assimilation might be carried on at the expense of the CO, 
provided by the respiration of the Bacteria themselves or by the 
decomposition of organie acids or other organie substances. 
That oxygen ean be evolved by chlorophyllaceous assimilation 
without any external CO, being present has been shown to be 
the case by Meyer * and others in all fleshy plants. 
By means of the gas-chamber and hanging-drops of B. Termo 
and of a very weak alkaline solution (0'5 °/, Na,CO,) of phenol- 
phthalein, it can readily be demonstrated that green alge, leaves 
of mosses, &c., exposed to optimal illumination in an atmosphere 
of H, evolve both traces of oxygen and traces of CO, simul- 
taneously. The same is the case with the coloured Bacteria, 
but here the evolution of oxygen and more especially the 
evolution of CO, are with fresh preparations under such con- 
ditions much stronger. Thus the green alge exposed to light 
in H evolve sufficient CO, to decolorize a drop of phenolphthalein 
* A. Meyer, Landwirthschaftliche Versuchs - Stationen, xxi. p. 227 et seg: 
E. L. M. Aubert, in Rey. gén, de Bot. 1892, pp. 421 & 558. 
