Chapter III The Chemical Unity of Living Beings
The varieties and essential unity of the protoplasm—Its affinity for oxygen—The chemical composition of protoplasm—Its characteristic substances.—§ 1. The different categories of albuminoid substances—Nucleo-proteids—Albumins and histones—Nucleins.—§ 2. Constitution of nucleins.—§ 3. Constitution of histones and albumins—Schultzenberger’s analysis of albumin—Kossol’s analysis—The hexonic nucleus.
The chemical unity of living beings corresponds to their morphological unity.
The Varieties and Essential Unity of the Protoplasm.—One essential feature of the living being is that it is composed of matter peculiar to it, which is called living matter, or protoplasm. But this is a somewhat incorrect way of expressing the facts. There is no unique living matter, no single protoplasm; their number is infinite, there are as many as there are distinct individuals. However like one man may be to another, we are compelled to admit that they differ according to the substance of which they are constituted. That of the first offers a certain characteristic personal to the first, and found in all his anatomical elements; similarly for the second. With Le Dantec we shall say that the chemical substance of Primus is not only of the substance of man, but in all parts of his body and in all his constituent cells it is the exclusive substance of Primus; and, in the same way, the living matter of another individual Secundus will carry everywhere his personal impress, which differs from that of Primus.
But it is none the less true that this absolute specificity is based with certainty only on differences which from the chemical point of view are exceedingly slight. All these protoplasms have a very analogous composition. And, if we regard as negligible the smallest individual, specific, generic, or ordinal variations we may then speak in a general manner of protoplasm or living matter.
Experiment shows us, in fact, that the real living substance—apart from the products it manufactures and can retain or reject—is in every cell tolerably similar to itself. The fundamental chemical resemblance of all protoplasms is certain, and thus we may speak of their typical composition. We may sum up the work of physiological chemistry for the last three quarters of a century by affirming that it has established the chemical unity of all living beings—that is to say, a very notable analogy in the composition of their protoplasm.
This living matter is essentially a mixture of the proteid or albuminoid substances, to which may be added other categories of immediate principles, such as carbohydrates and fatty matters. But the latter are of secondary importance. The essential element is the proteid substance. The most skilful chemists have tried for more than half a century to discover its composition. Only during the last few years—thanks to the researches of Kossel, the German chemist, following on those of Schultzenberger and Miescher—we are beginning to know the outer walls or the framework of the albuminoid molecule; in other words, its chemical nucleus.
Physical Characters of Protoplasm.—About 1860 Ch. Robin thought that he had defined living matter sufficiently—or, at least, as perfectly as could be expected at that time—by attributing to it three physical characteristics. They were:—Absence of homogeneity, molecular symmetry, and the association of three orders of immediate principles—albuminoids, carbohydrates and fats. These characteristics assist, but do not suffice, to define the organization.
No doubt the characteristics must be completed by the addition of a certain number of more subtle physical features.
One of them refers to the structure of protoplasm as revealed by the microscope. Throughout the whole of the living kingdom, from the bacteria studied by Kunstler and Busquet to the most complicated protozoa, protoplasmic matter presents the same constitution, and in consequence, this structure of the protoplasm must be considered as one of its distinctive characters. It is not homogeneous; it is not the last term of the visible organization: it is itself organized. Experiment shows that it does not resist breaking up or crushing. Mutilations cause it to lose its properties. As for the kind of structure that it presents, it may be expressed by saying that it is that of a foamy emulsion.
We saw above that our knowledge as to the physical condition of protoplasm has been completed by the theories of Bütschli’s micellæ or Pfeffer’s tagmata.
Properties of the Protoplasm. Its Affinity for Oxygen.—From the chemical point of view, living matter presents a very remarkable property—namely, a great affinity for oxygen. It absorbs it so greedily that the gas cannot remain in a free state in its neighbourhood. Living protoplasm, therefore, exercises a reducing power. But it does not absorb oxygen in this way for its own advantage; oxygen is not absorbed, as was supposed thirty years ago, to supply fuel wherewith to burn the protoplasm. The products are not those of its oxidation, of its own disintegration. They are the products of combustion of the reserve-stuff which is incorporated in it. These substances have been supplied to it from without, like the oxygen itself, with the blood. This was proved by G. Pflüger in 1872 to 1876. The protoplasm is only the focus, the scene, or the factor of combustion. It is not its victim, it does not itself furnish the fuel. It works like the chemist, who obtains a reaction with the substances that are given to him.
As for the reducing power of protoplasm, A. Gautier in 1881 and Ehrlich in 1890 have given fresh proofs. A. Gautier in particular has insisted that the phenomena of combustion take place, so to speak, outside the cell, and at the expense of the products which surround it; while on the contrary the really active and living parts of the nucleus and of the cellular body, work protected by the oxygen, as in the case of anaerobic microbes.
This result is of great importance. Burdon Sanderson, the late learned professor of physiology at the University of Oxford, has not hesitated to compare it to the discovery of respiratory combustion by Lavoisier. There is no doubt some exaggeration in the comparison; but there is, on the other hand, no less exaggeration in supposing that it is not of great importance. We may no longer in these days speak without reservation of the vital vortex of Cuvier, and of the incessant twofold movement of assimilation and dissimilation which is ever destroying living matter and building it up again. In reality, the living protoplasm varies very little; it only undergoes oscillations of very slight extent; it is the materials, the reserve stuff on which it operates, which are subject to continual transformations.
Chemical Composition of Protoplasm.—One of the the three characters attributed by Ch. Robin to living matter was its chemical composition, of which little was known in his time. He insisted on the constant presence in the living elements of three orders of immediate principles—proteid substances, carbohydrates, and fatty bodies. In reality the proteid substances, or albuminoids, alone are characteristic. The two other groups, carbohydrates and fatty bodies, are rather the signs and the products of the vital activity, than constituents of the matter on which it is exercised.
It is therefore on the knowledge of the proteid substances that all the sagacity of biological chemists has been exercised. Their efforts for thirty years, and particularly in the last few years, have not been barren; they enable us to give a first rough sketch of the constitution of these substances.