PRESIDENTIAL ADDRESS. 663 
which are present in the more fluid phases of the system—namely, in the 
cell juices. It is important to remember that changes in any one of these 
constituent phases, including the metaplasmic phases, must affect the equili- 
brium of the whole cell system, and because of this necessary equilibrium- 
relation it is difficult to say that any one of the constituent phases, 
such as we find permanently present in a living cell, even a metaplasmic phase, 
is less essential than any other to the ‘life’ of the cell, at least when we view 
it from the standpoint of metabolism. It is extremely difficult and probably 
impossible by any treatment of the animal to completely 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 significance 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 co-existence 
of metaplasmic glycogen, however small in amount, as upon the co-existence 
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 
dissolved in the cell juice, and, indeed, would hardly apply it to the highly 
differentiated parts of the bioplasm 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 microscopic studies, we recognise as ‘ undifferentiated ’ 
bioplasm. On ultimate analysis we can hardly 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 poly- 
phasic system. Certain of the phases may be separated, mechanically or other- 
wise, 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 co-existing 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 
reactions of the type which we have been discussing, occur in ordinary crystal- 
Icid 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 differen- 
tiated of animal cells—to consider, for instance, the ameba. 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 sugges- 
tive 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 ameba, though intracellular, is meta- 
plasmic. 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 must apply to 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 pro- 
teins of the bacteria or other food eaten by it may be inharmonious with their 
balance in the ameeba. 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 preparative processes also occur outside them. 
We need not think of a visible vacuole as the only seat of such changes. Similar 
fluid phases in the cell may elude the microscope, and the phenomena would be 
just as significant if reactions occur in the water imbibed by the colloids of the 
cell or present in the intra-micellar spaces of the bioplasm. It is always impor- 
tant to remember that 75 per cent. of the cell substance consists of water. 
All of these considerations we may apply to the tissue cells of the higher 
animal. To my mind, at least, the following considerations appeal. It is note- 
worthy that all the known complexes of the cell—the proteins, the phosphorous 
complexes, the nucleic acids, &c.—are susceptible to hydrolysis by catalytic 
