OXYGEN FROM COLOURED BACTERIA. 147 
all remains available for respiration, and only when it is used 
up does true intramolecular respiration commence. 
A further discussion of this point is at present inadvisable, 
but there can be no doubt that, just as in the case of intra- 
molecular respiration, when in the absence of free oxygen an 
evolution of CO, takes place at the expense of the combined 
oxygen held by the plasma, so in certain cases a special kind of 
respiration may take place for a short time after all external free 
oxygen has been removed—the oxygen contained in the CO, 
evolved being derived from a store of merely occluded oxygen, 
held either by the organism itself or by some product excreted 
by it. 
Evolution of Oxygen by other Coloured Bacteria. 
In these the pigment forms an integral part of the bacterial 
plasma, the oxygen being produced only by a process of assimi- 
lation, which requires an absorption of energy and ceases when 
the supply of radiant energy is cut off. 
Van Tieghem * has described two green Bacteria, Bacterium 
viride and Bacillus virens. In the latter the formation of 
colourless spores and germination of these in light to form 
greenish Bacillus-rods was noticed. Van Tieghem concluded 
that th e pigment was chlorophyll, and that the Bacteria could 
assimilate as green plants do, but did not produce any direct 
experimental proof whatever. The assumption that a green 
acterium must contain chlorophyll and be able to assimilate is 
quite unjustifiable, for certain pathogenic, undoubtedly sapro- 
phytic or parasitic Bacteria can produce a green pigment; and 
Gayon has shown that it is possible to extract from a small 
‘acterium Termo-like form growing on milk a green crystallizable 
ni insoluble in water and soluble in ether, alcohol, 
W (' &c. In these last forms, however, the pigment seems 
n excrete product, and not to form part of the bacterial 
Plasma, 
Engelmann + has 
bact , however, described an actively motile green 
o vem Which has the power of evolving in light minute traces 
“yen. The evolution of oxygen is extremely weak, and 
* . 
: = Tieghem, in Bull. Soc. Bot. France, xxvii. (1880) p. 174. 
W. Engelmann, in Bot. Zeit. 1882. 
