220 
NATURE 
[OcToBER 16, 1913 
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 re- 
actions 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, I 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 de- 
finite, 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 foodstuffs, only suffer change after they 
have become in a vague sense a part of such a giant 
molecule or biogen. Such assumptions became un- 
necessary 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 properties 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 re 
actions of which its molecule is normally capable. 
Exactly what sort of material might, in the cours 
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 ceil, in the 
modern phraseology of physical chemistry, is a system 
of coexisting phases of different constitutions. Cor- 
responding 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 equili- 
brium 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 ‘“ meta- 
plasmic’”’ constituents of the cell. These last com- 
prise 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 in- 
sisted upon—to comprise the diverse substances of 
smaller molecular weight and greater solubility, which 
are present in the more fluid phases of the system— 
namely, in the cell juices. It is important to remem- 
ber. that change in any one of these constituent 
phases, including the metaplasmic phases, must 
affect the equilibrium of the whole cell system, 
and because of this necessary equilibrium-relation it 
is difficult to say that any one of the constituent 
3 See in this connection the very able exposition of the views developed by. 
Zwaardemaker and others, by Botazzi in Winterstein’s ‘‘ Handbuch,” vol. i, 
NO. 2294, VOL. 92] 
phases, such as we tind permanently present in a_ 
living cell, even a metaplasmic phase, 1s less essential. 
than any other to the “life” of the cell, at least when 
We view it from the point of view of metabolism. It is 
extremely difficult and probably impossible by any 
treatment of the animal completely to deprive the liver — 
of its glycogen deposits, so long as the liver cells” 
remain alive. Even an extreme variation in the 
quantity is in the present connection without signi-— 
hieance because, as we know, the equilibrium of a 
polyphasic system is independent of the mass of any 
one of the phases; but I am inclined to the bold 
statement that the integrity of metabolic life of a 
liver cell is as much dependent on the coexistence of — 
metaplasmic glycogen, however small in amount, as- 
upon the coexistence of the nuclear material itself; 
so in other cells, if not upon glycogen, at least upon 
other metaplasmic constituents. 
Now we should refuse to speak of the membrane 
of a cell, or of its glycogen store, as living material. 
We should not apply the term to the substances dis- 
solved in the cell juice, and, indeed, would scarcely 
apply it to the highly differentiated parts of the bio- 
plasm if we thought of each detail separately. We are 
probably no more justified in applying it, when we 
consider it by itself, to what, as the result of micro- 
scopic studies, we recognise as ‘undifferentiated ’’ 
bioplasm. On ultimate analysis we can scarcely speak 
at all of living matter in the cell; at any rate, we 
cannot, without gross misuse of terms, speak of the 
cell life as being associated with any one particular 
type of molecule. Its life is the expression of a- 
particular dynamic equilibrium which obtains in a 
polyphasic system. Certain of the phases may be 
separated, mechanically or otherwise, as when we 
squeeze out the cell juices, and find that chemical 
processes still go on in them; but “life,” as we 
instinctively define it, is a property of the cell as a 
whole, because it depends upon the organisation of — 
processes, upon the equilibrium displayed by the 
totality of the coexisting phases 
I return to my main point. The view I wish to 
impress upon you is that some of the most important 
phenomena in the cell, those involving simple re- 
actions of the type which we have been discussing, 
occur in ordinary crystalloid solution. We are 
entitled to distinguish fluid (or more fluid) phases in 
the cell. I always think it helpful in this connection 
to think of the least differentiated of animal cells— 
to consider, for instance, the ameceba. In _ this 
creature a fluid phase comes definitely into view with 
the appearance of the food vacuole. In this vacuole 
digestion goes on, and there can be no doubt, from 
the suggestive experimental evidence available, that 
a digestive enzyme, and possibly two _ successive 
enzymes (a pepsin followed by a trypsin) appear in 
it. It is now generally admitted that digestion in 
the amoeba, though intracellular, is metaplasmic. 
The digestion products appear first of all in simple 
aqueous solution. Is it not unjustifiable to assume 
that the next step is a total ‘‘assimilation” of the 
products, a direct building up of all that is produced 
in the vacuole into the complexes of the cell? If 
there be any basis for our views concerning the speci- 
ficity of, say, the tissue proteins, they mus apis S 
the amceba no less than to the higher animal, and 
we must picture the building-up of its specific com- 
plexes as a selective process. The mixture of amino- 
acids derived from the proteins of the bacteria or 
other food eaten by it may be inharmonious with 
their balance in the amceba. Some have to be more 
directly dealt with, by oxidation or otherwise. If 
the digestive hydrolysis occur outside the complexes, 
we may most justifiably assume that other prepara- 
