52 
COLOUR IN NATURE 
CHAP. 
coloured Bacterium found in stagnant river-water, 
in which the peculiar pigment was confined to the 
protoplasm of the individuals and did not extend 
into the jelly surrounding the colonies. Mr. Slater 
has similarly described a form producing a bright 
red pigment which is confined to the cells. On the 
other hand, in the case of Micrococcus prodigiosus, 
the red pigment is confined to the masses of 
mucilage surrounding the colonies and does not 
occur within the cells at all, while in yet other cases 
the pigment may be found only in the substance in 
which the colonies are living. 
As to the conditions under which the pigments 
are produced, it is well known that Micrococcus pro¬ 
digiosus loses its power of producing pigment at high 
temperatures, while light is necessary for the produc¬ 
tion of the purple pigment of Beggiatoa roscopersicina. 
This pigment is of especial interest because, according 
to Engelmann (1888), its presence in the organism is 
associated with the power of breaking up carbonic 
acid and setting free oxygen, therefore it has a 
function equivalent to that of the chlorophyll of 
green plants. In the case of Bacillus pyocyaneus , 
according to Gerrard, the power of pigment produc¬ 
tion is dependent upon the nature of the medium, as 
well as upon the particular race of the microbe. 
As a point of interest with regard to the chemical 
nature of the pigments, we may notice that in 1889 
Zopf described a yellow pigment formed by Bacterium 
egregium as a lipochrome, and stated that this was the 
first time that lipochromes had been described as 
products of bacterial action ; he has since described 
other cases. The bright red Micrococcus pigment is 
