662 TRANSACTIONS OF SECTION I. 
metabolism in compartments. It is from the behaviour of simple molecules we 
are learning our most significant lessons. 
Now interest in the chemical events such as those we have been dealing with 
may still be damped by the feeling that, after all, when we go to the centre 
of things, to the bioplasm, where these processes are initiated and controlled, 
we shall find a milieu so complex that the happenings there, although they 
comprise the most significant links in the chain of events, must be wholly obscure, 
when viewed from the standpoint of structural organic chemistry. I would 
like you to consider how far this is necessarily the case. 
The highly complex substances which form the most obvious part of the 
material of the living cell are relatively stable. Their special characters, and in 
particular the colloidal condition in which they exist, determine, of course, 
many of the most fundamental characteristics of the cell: its definite yet mobile 
structure, its mechanical qualities, including the contractility of the protoplasm, 
and those other colloidal characters which the modern physical chemist is studying 
so closely. For the dynamic chemical events which happen within the cell, these 
colloid complexes yield a special milieu, providing, as it were, special apparatus, 
and an organised laboratory. But in the cell itself, I believe, simple molecules 
undergo reactions of the kind we have been considering. These reactions, being 
catalysed by colloidal enzymes, do not occur in a strictly homogeneous medium, 
but they occur, 1 would argue, in the aqueous fluids of the cell under just such 
conditions of solution as obtain when they progress under the influence of 
enzymes in vitro. 
There is, I know, a view which, if old, is in one modification or another still 
current in many quarters. This conceives of the unit of living matter as a 
definite, if very large and very labile molecule, and conceives of a mass of living 
matter as consisting of a congregation of such molecules in that definite sense 
in which a mass of, say, sugar is a congregation of molecules, all like to one 
another. In my opinion, such a view is as inhibitory to productive thought as 
it is lacking in basis. It matters little whether in this connection we speak of 
a ‘molecule’ or, in order to avoid the fairly obvious misuse of a word, we use 
the term ‘biogen,’ or any similar expression with the same connotation. 
Especially, I believe, is such a view unfortunate when, as sometimes, it is made 
to carry the corollary that simple molecules, such as those provided by food- 
stuffs, only suffer change after they have become in a vague sense a part of 
such a giant molecule or biogen. Such assumptions became unnecessary as soon 
as we learnt that a stable substance may exhibit instability after it enters the 
living cell, not because it loses its chemical identity, and the chemical pro- 
perties inherent in its own molecular structure, by being built into an unstable 
complex, but because in the cell it meets with agents (the intracellular 
enzymes) which catalyse certain reactions of which its molecule is normally 
capable. 
Exactly what sort of material might, in the course of cosmic evolution, have 
first come to exhibit the elementary characters of living stuff, a question raised 
in the Presidential Address which so stirred us last year, we do not, of course, 
know. But it is clear that the living cell as we now know it is not a mass of 
matter composed of a congregation of like molecules, but a highly differentiated 
system ; the cell, in the modern phraseology of physical chemistry, is a system of 
co-existing phases of different constitutions.° Corresponding to the difference in 
their constitution, different chemical events may go on contemporaneously in the 
different phases, though every change in any phase affects the chemical and 
physico-chemical equilibrium of the whole system. Among these phases are 
to be reckoned not only the differentiated parts of the bioplasm strictly defined 
(if we can define it strictly) the macro- and micro-nuclei, nerve fibres, muscle 
fibres, &c., but the material which supports the cell structure, and what have 
been termed the ‘metaplasmic’ constituents of the cell. These last comprise 
not only the fat droplets, glycogen, starch grains, aleurone grains, and the like, 
but other deposits not to be demonstrated histologically. They must be 
held, too—a point which has not been sufficiently insisted upon—to comprise 
the diverse substances of smaller molecular weight and greater solubility, 
° See in this connection the very able exposition of the views developed by 
Zwaardemaker and others, by Botazzi in Winterstein’s Handbuch, vol. i. 
