The commonwealth of cells

by H. G. F. Spurrell

To say, however, that an animal’s body consists of cells is to take an entirely wrong starting-point. A cell is complete in itself, and can live if properly fed, even though separated from its neighbours. Many whole animals consist of only one cell. A cell is, moreover, capable of growing and dividing, thus giving rise to two cells with two nuclei, and it is only because cells find that it pays better not to separate, but to form masses and specialize at different kinds of work, that we have large animals composed of millions of cells like ourselves.

Given a cell, it is necessary to keep that cell under favourable conditions. Otherwise the unstable protoplasm breaks up. It must have the elements necessary to keep up its cycle of changes in the proper form, which we may now call food, and many cells have to go and find this requisite. It must keep away from injurious influences, and it must race other cells for localities favourable to its growth and multiplication; in fact, the cell must work.

That a cell can, in virtue of its chemical affinities alone, move about, seeking favourable conditions, showing discrimination and doing work, seems incomprehensible. In the first place, how can it move? There is only one way: it must effect a redistribution of its substance, and contrive that those parts of the cell whose activity is applied to this end shall be so situated as to produce definite changes in its shape according to the cause which evokes them. Of the way in which different cells move we shall have a good deal more to say later.

Why protoplasm should be influenced to move still requires explanation. Yet the gap between protoplasm and other substances is really not so great, after all. Heat and magnetism cause movement in inanimate matter, and the response of protoplasm as exemplified by some of the minute unicellular animals is almost as mechanical. Some kinds which swim in water move to the positive pole of a galvanic battery, others to the negative, if the wires are dipped into the vessel containing them. Some move towards light, others away from it, with unvarying regularity. Temperature and chemical substances also cause a definite effect upon these micro-organisms. And all these movements are wholly involuntary, absolutely invariable, and, in fact, reactions evoked by fixed causes.

Nevertheless, it will be seen that protoplasm can only continue to exist in the form of a cell, since, unless thus organized, it can neither keep itself among favourable surroundings nor prepare fresh ingredients to make good its waste. If a cell be cut up into several pieces, these detached bits of protoplasm will live for a time; but death overtakes them as soon as they have used up their reserve material. When this is gone, they have to consume their own substance, a process which quickly proves fatal. Should a fragment contain a small part of the nucleus cut away with it, it will live a little longer; but it is only the piece which contains the nucleus more or less intact—in other words, the cell, damaged though it be—which can survive and recover from such mutilation.

The specialization of protoplasm to form a cell is perhaps its most remarkable peculiarity. Not only is protoplasm differentiated to form different structures, but it devotes the energy evolved in its ceaseless change to different purposes. The protoplasm of the motor organs of the cell expends itself wholly in producing the physical movements necessary to approach and capture food. When this has been passed into the cell, protoplasm of another variety works to refine and dissolve it, and then passes it on to the nucleus. The protoplasm of the nucleus, again, has different work to do. It devotes its energy to producing chemical changes in the raw material, and converting it into new compounds which the various parts of the cell can assimilate. Some of these it retains for its own needs; the rest it dispenses to the motor and other organs to repair their waste, and supply them with energy to obtain more food.

Thus do the different varieties of protoplasm which compose a cell supply one another’s needs, and enable one another to live; and thus does a cycle of chemical changes form the foundation upon which the whole fabric of life rests. But into details we cannot yet go, for our investigations of the material basis of life have not yet carried us beyond these general conclusions.

At present we know nothing definite about the first causes of life, and, though we have hopes, perhaps we never shall. Meanwhile we are observing, analyzing, and classifying the phenomena in which life is manifested, in the hope that at last light may break through upon our researches, and we may be able, if not to synthesise protoplasm in a test-tube, at least to demonstrate its workings in equations.

In the meantime, our actual knowledge of living matter can still be compressed into the words in which Professor Huxley summed it up years ago:

‘Carbon, hydrogen, oxygen, and nitrogen are all lifeless bodies. Of these, carbon and oxygen unite, in certain proportions and under certain conditions, to give rise to carbonic acid; hydrogen and oxygen produce water; nitrogen and hydrogen give rise to ammonia. These new compounds, like the elementary bodies of which they are composed, are lifeless. But when they are brought together under certain conditions they give rise to the still more complex body, protoplasm, and this protoplasm exhibits the phenomena of life.’