II 
THE PIGMENTS OF ORGANISMS 
33 
when exposed to sunshine can decompose carbonic 
acid and set free oxygen, and that it is by virtue of 
their chlorophyll that they can do this, but beyond 
this we have nothing but a host of rival theories. 
The most interesting of these is perhaps that of 
Schunck, who considers that chlorophyll carries 
carbonic acid from the air to the assimilating proto¬ 
plasm, just as hsemoglobin carries oxygen. Macallum 
holds that chlorosis in plants and animals is due 
to the same cause, the absence or deficiency of 
iron in the nuclear chromatin ; and this in spite of 
the fact that it is improbable that chlorophyll con¬ 
tains iron. Thus the absence of chlorophyll in a 
plant grown without iron is only one of the con¬ 
sequences of the general unhealthiness. In reference 
to this view of Macallum’s, it is interesting to note 
that according to Nencki there is a close relation 
between haematoporphyrin, a derivative of haemo¬ 
globin, and one of the derivatives of chlorophyll 
green. 
As is well known, chlorophyll is, at any rate in 
solutions, an extremely unstable pigment, fading in 
light with great rapidity. In natural conditions 
it is associated with one or more pigments belonging 
to a widely spread group of pigments—the lipo- 
chromes, characterised by their colour, which varies 
from red to yellow, as well as by other properties. 
It is uncertain whether these subsidiary pigments 
exercise any influence in the process of assimilation, 
or whether it is not the true chlorophyll or chloro¬ 
phyll green which is alone active. Lipochromes are 
not the only pigments which occur in association 
with chlorophyll, but the subject will be treated 
D 
