ium from the
chlorophylls,

H HC===CH
| | |
CH_{3}-C--C C---C
| \\ // |
| N N |
| / . . \ |
C_{2}H_{5}-C--C . . C---CH
\ . . //
C------------C
/ . . \
C_{2}H_{5}-C==C . . C==C-C_{2}H_{5}
| \ .. / |
| N-----Mg-----N |
| / \ |
CH_{3}-C==C C==C-C_{2}H_{5}
| |
CH_{3} CH_{3}

AEtiophyllin

H HC===CH
| | |
CH_{3}-C--C C---C
| \\ // |
| N N |
| / \ |
C_{2}H_{5}-C--C C---CH
\ //
C------------C
/ \
C_{2}H_{5}-C==C C==C-C_{2}H_{5}
| \ / |
| N N |
| / \ |
CH_{3}-C==C C==C-CH_{3}
| |
CH_{3} CH_{3}

AEtioporphyrin

The COOH groups which are attached to these compounds to form the various
phyllins and porphyrins, as well as the original chlorophylls, are supposed
to be attached to the C_{2}H_{5} groups in the above formulas, the
different modifications, or compounds, depending upon the position in which
one or more of these attachments are made.

SIMILARITY OF CHLOROPHYLL AND HAEMOGLOBIN

It seems to be desirable, at this point, to call attention to the
remarkable similarity in the chemical composition of chlorophyll, the most
important pigment of plants, and haemoglobin, t