124 DR. A. J. EWART ON THE EVOLUTION OF 
bacterial plasma. If, however, the oxygen were held in a loose 
and readily available form, occluded or in loose chemical com- 
bination, it should be possible to detect the presence of such 
oxygen by chemical, physical, or biological methods. 
The fact that certain coloured Bacteria can, when exposed to 
light, evolve traces of oxygen has now for some time been 
known. Engelmann * has described a motile green bacterium, 
which possesses a faint power of assimilation, and also states 
that the same power may be shown by the “ Purpur-Bakterien," 
in which not chlorophyll but a different pigment, “ Bakterio- 
purpurin,” having a totally different absorption spectrum to 
that of chlorophyll, is present. The main absorption of bacterio- 
purpurin takes place in the ultra-red; and Engelmann has 
succeeded in establishing the fact that the red Bacteria are 
capable of relatively fairly active assimilation when exposed to 
the invisible ultra-red heat-rays. 
Since Engelmann no other author has published anything 
bearing directly on this question, though such epoch-making 
researches are naturally always in need of confirmation and 
corroboration. Many other Bacteria also are coloured or have 
the power of forming pigments; but the question as to what the 
utility of these pigments may be has never been answered 
satisfactorily, and has only in a very few cases even been 
attempted. 
Thus Beyerinck t considers that in what he terms parachromo- 
phoric Bacteria the pigment is to be regarded as an excrete 
waste or by-product of destructive metabolism. The same is 
probably the case with the chromoparie Bacteria (Bacillus 
cyaneo-fuscus, B. cyanogenus, B. pyocyaneus, B. virescens, 
B. prodigiosus). On the other hand, in chromophoric Bacteria, 
in which Beyerinek includes the green, red, yellow, and brown 
Bacteria, which do not fluidify gelatine, the pigment, since 1t 
forms an integra] part of the bacterial plasma so long as this p 
living, must have an important biological meaning. One poss 
bility is that the pigments in these cases are assimilatory 
pigments like chlorophyll, etiolin, and  bacterio-purpurin. It 
was with the intention of determining this point, and also 0 
* T. W. Engelmann, in Bot. Zeit. 1882 and Oct. 1888. t 
t M. W. Beyerinck, in Bot. Zeit. 1891 : “ Die Lebensgeschichte einer Pigmen” 
Bakteri.” 
