452 
The monograph is not merely a reprint of the 
numerous papers from Liebig’s Annalen, but 
starts, in the first chapter, with a useful summary 
of all the results obtained up to the date of issue, 
and the relationship of the various substances iso- 
lated during the course of the researches is clearly 
indicated in tabular form. The book concludes 
with a description of some researches, most of 
which receive their first publication in this volume, 
on the pigments of the blood and their derivatives, 
and throw further light on the chemical relation- 
ship between the green pigment of plants and the 
red pigment of the blood, amplifying in a striking 
manner the earlier investigations of Hoppe-Seyler, 
Schunck, Nencki, and others. 
It is difficult to select from such a mass of new 
material points for special mention in a short re-. 
view. As an example, however, of the immense 
amount of patience and skill required in the pre- 
paration of chemically-pure preparations, the 
separation of chlorophyll into its components a 
and b, described on p. 163 et seq. may be cited; 
to obtain only a preliminary separation of the two 
substances contained in 8 grams of a mixture, no 
fewer than fourteen extractions of the solution in 
light petroleum with methyl alcohol were required, 
and 2 litres of the alcohol were employed for each 
extraction. Experimental details of this character 
are of interest, in that they illustrate the great 
technical difficulties of modern biochemical re- 
search, and the necessity of a somewhat costly 
equipment for laboratories devoted to this object; 
it is doubtful, indeed, whether the talent of a Will- 
statter would have availed in accomplishing what 
is described in this monograph, had there not 
been, in the first place, ample funds for the supply 
of the necessary material and apparatus, and in |! 
the second place, the cooperation of several ac- 
complished students. The book contains many 
other examples of brilliant experimental technique, 
and for this reason alone it is well werthy cf 
perusal by all chemists whose work entails large- 
scale laboratory operations. 
Of the results of scientific interest, attention 
may, in the first place, be directed to the confirma- 
tion of the statement of Stokes, published in 1864, 
based on spectroscopic examination, that the 
chlorophyll of land-plants contains no fewer than 
four pigments. To this investigator and to 
Kraus and Sorby are due the principles of the 
method which, in the hands of Willstatter and his 
pupils, has finally led to the isolation of all the 
four pigments in a chemically-pure form. 
Of great interest also, is the discovery of the 
fact that magnesium is an essential part of the 
chlorophyll molecule, just as iron forms an_ in- 
NO: 233 Taal Ot 
NATURE 
_ presence of chlorophyll still 
[JuLy 2. 2@r4 
tegral part of the molecule of the blood-pigment. 
No less interesting is the discovery of the alcohol, 
phytol, and of the enzyme phytase, an example of 
a new species of ferment capable of acting in 
alcoholic solutions. Mention must also be made 
of the mysterious change, designated by Will- 
statter ‘“‘allomevisation,” which takes place, ap- 
parently under the influence of some catalyst in 
alcoholic solution the exact nature of which has 
not yet been explained. . 
Although the results so far obtained do not 
warrant the assignment of a definite formula to 
the two chlorophylls, the general character of these 
pigments and of hemin appears to be fairly well 
established. The recent valuable work of Piloty, 
Hans Fischer, and others on the synthesis of 
various pyrrole derivatives has also materially 
aided in the elucidation of the complex formule 
of these pigments. It is to be hoped that the 
publication of the researches on chlorophyll in 
their present form will afford a stimulus to re- 
search on plant physiology. The vexed question 
as to the mechanism of the sugar synthesis in the 
remains unsolved, 
and the fact that it is now possible to obtain the 
separate pigments of the leaf free from all con- 
taminations should materially assist in the solution 
of this problem. Certain interesting suggestions 
as to the relationship of the pigments to one an- 
other, and as to their biological functions, are 
made in this monograph, which opens great vistas 
of future research. 
(2) It is now nine years since the first edition 
of Prof. Czapek’s two bulky volumes on the 
general chemistry of plants was issued, and it 
may be regarded as a favourable sign that a com- 
plete new edition of a work of this magnitude 
should be called for so soon. The first 240 pages 
of the present issue deal chiefly with general bio- 
logical problems, including those relating to the 
physical structure of the cell, a subject which has 
received much attention from plant physiologists 
in recent times as a result largely of Prof. Cza- 
pek’s own researches. The remainder of the 
volume is devoted to the special biochemistry of 
the sugars, fats, and lipoids, which are treated 
both from the more nurely chemical and the 
physiological point of view. Books of reference 
of this description are indispensable nowadays to 
workers on biological chemistry, when the results 
of recent investigations are dispersed amongst so 
many journals. We owe, therefore, a great debt 
of gratitude to Prof. Czapek for his labours in 
collecting together a heterogeneous mass_ of 
material and issuing it in a form in which it can 
be readily reviewed. Ss: Be 
