362 
NATURE 
[AucusT 17, 1899 
Inulase, which decomposes inulin ; Cyz¢ase, which hydro- 
lyses cellulose. 
(2) Those which transform more complex sugars into 
simpler compounds of the same class—e.g. Jnuvertase, 
which attacks cane-sugar ; G/ucase, which splits up 
maltose, and others. 
(3) Those which break up glucosides into some sugar 
and an aromatic body—e.g. Emulsin, which decomposes 
the amygdalin of almonds into sugar and prussic acid ; 
Myrosin, which breaks up the sinigrin of mustard into 
a sugar and the pungent substance so well known. 
(4) Proteolytic enzymes, such as Pepsin and Trypsin, 
which decompose insoluble and indigestible proteids 
into soluble and digestible peptones and other bodies, 
and play so important a part in digestive processes 
generally. 
(5) The clotting enzymes which bring about coagul- 
ations—e.g. Rennet, so important in converting milk into 
cheese ; Zhrombase, the enzyme concerned in the co- 
agulation of blood ; Pectase, the chief agent in forming 
vegetable jellies. ; 
(6) The ZLzfases, concerned in decomposing oils and 
fats. 
(7) The Oxydases, a curious class of enzymes recently 
shown to be active in carrying oxygen and bringing about 
the oxidation of certain vegetable juices—e.g. Laccase, 
concerned in the formation of lacquer varnish. 
(8) A number of enzymes as yet unclassified—e.g. 
Urease, which induces the formation of ammonium car- 
bonate from urea, and the newly discovered “‘zymase ” of 
Buchner—the alcohol producing enzyme. 
It is, of course, impossible in a review to go far into 
particulars concerning these numerous forms, of which, 
moreover, there are many varieties. On reading Dr. 
Green’s admirable and exhaustive account of them, the 
student will be struck with the prominent position which 
the study of plants occupies in the elucidation of the 
properties of enzymes. It has been far too fashionable 
in this country to regard enzymes and the study of 
fermentation as if they were in some way specially ac- 
credited to the domain of the chemist, whereas inasmuch 
as any such specialisation can be insisted upon, the study 
is far more within the domain of the botanist and the 
physiologist, a fact very clearly brought out in this book ; 
as are also many of the important bearings of the study 
on the numerous applications of botanical science in 
the arts. 
Secondly, it is worth remarking, in full view of the 
industrious and valuable work done by able continental 
botanists and physiologists, how conspicuous are the 
researches of English investigators in this department of 
science during the last few years, denoting a phase of 
activity on the part of our physiologists and botanists 
which promises well in the future. The author has 
collected a long list of authorities, and since he has made 
the study of fermentations peculiarly his own for some 
years, we may accept the literature as practically com- 
plete. At the same time, in view of the remarks on 
p- 75, we should have expected some quotation of Mr. 
Parkin’s recent and important paper on the inulins in 
monocotyledons. 
In view of the modernity of the study of enzymes, we 
NO. 1555, VOL. 60] 
can hardly be surprised at the lack of any complete 
deductive explanation of their action, though one of the 
most interesting sections of the book is that discussing 
the various hypotheses raised. Our ignorance of the 
constitution of enzymes no doubt stands at the bottom of 
this, and it is not at present clear what is meant by a 
soluble enzyme or by solution. But the fatal blocks to 
progress in the study of their constitution so far have 
been their instability during separation, and the un- 
certainty as to their purity ; consequently the analyses 
so far attempted cannot be relied on, and we do not even 
know of any enzyme that it is proteid in nature. All we 
can be sure of is that a given watery extract washes out 
from living protoplasm a something—which we term an 
enzyme—which is capable of converting enqrmous 
masses of some other body—e.g. sugar—and can itself 
be mechanically precipitated, re-dissolved and so on. 
This precipitate may even be dried and retain its specific 
powers on re-solution. Whether the precipitate consists 
principally of the enzyme itself or of some body or 
bodies to which it is attached, is an unsolved question. 
But when active and in solution, it is significant that 
the properties of an enzyme can be destroyed ina few 
moments by raising the temperature beyond a (relatively 
low) maximum, and that the activity rises and falls 
with a scale of temperature between the limits; on the 
other hand, it differs from a living organism in being 
capable of exerting its specific power in presence of an 
antiseptic. 
In the discussion regarding fermentation as a chemical 
process, these facts should not be overlooked, and it is 
as true to-day as it was in Pasteur’s time, that you can- 
not have fermentation without life. 
No matter how “ dead” an enzyme may be ; no matter 
whether its remarkable energy consists in surface-actions 
or in vibrations propagated through the solution, in tem- 
porary chemical unions and disunions or in electrical 
hydrolysis ; and no matter what its chemical analyses 
may imply as to its proteid nature—the fact must be 
maintained that enzymes are built up by living proto- 
plasm, and normally exert their best actions in con- 
nection with the living cell. In many respects, indeed, 
they suggest essential bits of the protoplasm, and in many 
ways remind us that we have not yet done with the 
physiological or “ vital” theory of fermentation, and this 
will, we think, strike most readers, though perhaps Dr. 
Green’s summing up inclines more to the view that 
fermentation is a purely chemical process. Not the least 
important prop to the chemical theory of enzyme-action 
is furnished by Croft Hill’s recent work on the action of 
maltase or glucase on malt-sugar, and his remarkable 
discovery that a reversal of the enzyme-action may 
occur, reminding us of the reversals occurring in certain 
chemical processes. 
Here, however, we must stop. It is not necessary to 
recommend the perusal of the book to all interested in 
the subject, since it is indispensable to them, and we 
will merely conclude by congratulating the Cambridge 
Press on having added to their admirable series of 
Natural Science Manuals an eminently successful work 
on so important and difficult a theme, and the author 
on having written a treatise cleverly conceived, indus- 
