The commonwealth of cells

by H. G. F. Spurrell

Having now roughly sketched out the scheme upon which such a body works, we can go on to a more detailed examination of the division of the labour, and the way in which each department supplies, and is dependent upon, the others. If we were to do this thoroughly, it would take a great deal of time and space, for the physiology of a potato plant, though essentially the same, presents many differences from that of a horse; but the physiology of the great human interest is also that of the most complicated animal, namely, man, so it is on him that we shall focus our attention.

Protoplasm is more easily studied the more specialized is the animal it composes. When all the events of life are taking place in a speck of matter, invisible without a microscope, it is impossible to analyze the changes which it is working in its surroundings, or to infer those which are going on in itself. But when large numbers of cells are examined collectively, we can deal with what they take in and what they give out in sufficient bulk to arrive at a fairly accurate determination. The study is rendered still easier in an animal with extremely specialized organs, like man, in which food is nearly all taken in by the mouth, and thus kept quite distinct from what is eliminated; the latter, again, being mostly given off by the kidneys is kept equally distinct. Moreover, the intermediate changes being performed in different organs still further simplifies investigation of the vital process; for the physical effects are also more easily studied when exaggerated in a particular part of the animal. The electrical changes in a single cell might long have remained unsuspected had we not been able to observe those in a muscle with the galvanometer.

Now, while the cells which make up the body of man differ very greatly owing to the different tasks which they have to perform in obtaining food and getting rid of refuse, they all require very much the same fuel to enable them to live, and having got it, they all treat it in very much the same way; therefore our first business is to consider what the body wants, and what it does with it. Afterwards we can try to find out how it gets it, and where.

The first and most indispensable requirement of protoplasm is water. The next is probably nitrogen, compounds of which seem to form the framework of the protoplasmic structure. The next is probably carbon, and the next free oxygen. The two last-mentioned combine with a release of energy. This happens in the grate when coal burns, and the result is heat. In the tissues of a body the result may be heat, growth, or movement, all three being present in the phenomenon of muscular activity. Finally there are mineral salts, the most important being sodium chloride, which is placed on the table at every civilized meal.

But though these elements are given here in order, their importance is really equal, for all are necessary. That is about as much as it is wise to say here. The chemistry of the living cells—their anabolism, or how fresh material is built into their structure; their katabolism, or how the same structure is broken down that work may be done; in fact, the general metabolism—is so complicated, and so little understood as yet, and requires so extensive a knowledge of chemistry to follow, that it is best left alone by people who do not want to go into it deeply. At best, such a discussion resolves itself into an exposition of different observers’ theories, with the reasons why they hold them—reasons based on laborious and technical studies. Pages might be written on the various theories, backed by pages more of chemical formulæ, to show why this view deserves deep consideration, while that, in spite of the obstinacy with which it is upheld, is absurd; but though such discussions take one nearest the secret of life, the general public is not unnaturally apt to stigmatize this side of physiology as dry. It is a matter which interests experts, not the casual reader.

Quite a different affair is the question of diet. That is everybody’s business, as the number of faddist societies and blatantly advertised ‘foods’ attest. And though the preparation of the food in the body up to the point where it merges into living matter and is lost sight of—in a word, ‘digestion’—is again a question of chemistry, it is one which may be approached without such an exhaustive knowledge of that science as the previous considerations would have required. It is, moreover, to judge from the way it is discussed, a topic of universal interest.

A casual glance at the animal kingdom will show that diet is a wide subject. A pigeon will eat peas; a tiger would not know what to do with the peas if he got them; while a monkey will eat almost anything he can lay hands on. A plant takes us still further afield, for it can use the atoms of substances with an extremely simple molecule—carbonic acid gas, for instance.

Our task, however, is simplified by our having only man to consider; and although most of the higher animals are so much alike that they might be considered in general and contrasted in detail, it is a great thing to get rid of the whole vegetable kingdom with bacteria and parasitic animals.

One of the first requisites for the maintenance of life, as was mentioned above, is nitrogen. Now, nitrogen is one of the commonest elements in the world, but it is the hardest to supply to the body. Four-fifths of the air is pure nitrogen, but pure nitrogen is useless as a food. We draw it into our lungs at every breath, and are none the better for it, for we breathe it out again unchanged; and if it were completely absent from the air we should not be so very much the worse. The Ancient Mariner exclaimed, ‘Water, water everywhere, and not a drop to drink’; a starving man might exclaim, ‘Nitrogen, nitrogen everywhere, and not an atom to assimilate.’