49 SECTIONAL ADDRESSES. 
continuously, and in health unerringly, completing a series of chemical 
changes so numerous and so diverse, must produce in every thoughtful 
mind a sensation of humble amazement. The aspect of this miraculous 
organisation which requires most to be emphasised, however, is that an 
appreciation of its complex beauty can be gained only by those to whom 
at least the elements of a training in chemistry have been vouchsafed. 
Such training has potential value from an ethical standpoint, for 
chemistry is a drastic leveller; in the nucleic acids man discovers a kin- 
ship with yeast-cells, and in their common failure to transform uric 
acid into allantoin he finds a fresh bond of sympathy with apes. The 
overwhelming majority of people arrive at the grave, however, without 
having had the slightest conception of the delicate chemical machinery 
and the subtle physical changes which, throughout each moment of life, 
they have methodically and unwittingly operated. 
Chlorophyll and Hemoglobin. 
To those who delight in tracing unity among the bewildering 
intricacies of natural processes, and by patient comparison of super 
ficially dissimilar materials triumphantly to reveal continuity in the 
discontinuous, there is encouragement to be found in the relationship 
between chlorophyll and hemoglobin. Even the most detached and 
cynical observer of human failings must glow with a sense of worship 
when he perceives this relationship, and thus brings himself to acknow- 
ledge the commonest of green plants among his kindred. Because, justi 
as every moment of his existence depends upon the successful 
performance of its chemical duties by the hemoglobin of his blood 
corpuscles, so the life and growth of green plants hinge on the trans- 
formations of chlorophyll. 
The persevering elucidation of chlorophyll structure ranks high in 
the achievements of modern organic chemistry, and in its later stages 
is due principally to Willstatter and his collaborators, whose investiga- 
tions culminated in 1913. Eliminating the yellow and colourless 
companions of the substance by a regulated system of partition among 
solvents, they raised the chlorophyll content to 70 per cent. from the 
8 to 16 per cent. found in the original extract, completing the separation 
by utilising the insolubility of chlorophyll in petroleum ether. By 
such means, 1 kilogram of dried stinging-nettles gave 6.5 grams of the 
purified material, representing about 80 per cent. of the total amount 
which the leaf contains, and application of the process to fresh leaves 
has established the identity of the product from both sources. Thus 
the isolation of chlorophyll from plants is now no more difficult than 
that of alkaloids or of sugars, and may actually be demonstrated as a 
lecture-experiment. 
As a consequence of these operations the dual nature of leaf-green 
was brought to light in 1912. The focus of main phytochemical action 
is thus revealed as a system composed of chlorophyll-a, bluish-green 
in solution, and of the yellowish-green chlorophyll-b, representing 
different stages of oxidation as indicated by the formule, 
(a) CyoHy9ON«Mg(CO.CHg) (COs.CopHyo) = Cs5H720;NyMg 
(6) CxoHy402NyMg(CO2CHg) (COo.CopH go) = Css OgNaMg 
