Читать книгу The Body at Work: A Treatise on the Principles of Physiology онлайн

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If it were possible by a process of elimination to ascertain the substances which must be present in protoplasm, the physiologist might formulate a reasonable hypothesis as to the nature of this “basis.” But there is no part of any living thing, or, at any rate, no part which is not microscopic in its dimensions, which can be pointed out as protoplasm and nothing besides. It is impossible to isolate anything which can be described as pure protoplasm. Nor is it possible, by comparing various tissues which are acknowledged to be rich in protoplasm, to ascertain what chemical substances are common to them all.

If it were feasible, by analysing a number of specimens of protoplasm, to make sure that, although x is absent from one, y from another, and z from a third, some one thing, P, is always present, then P might be regarded as the physical basis, even though it were evident that P alone was not protoplasm. Protoplasm would be P combined with either x, y, or z. Globulins and albumins and other proteins are always present, but in varying proportions; but it is impossible to make certain that either of these chemical substances is more important than the rest. Nor is it possible to assert of either that it is essential.