physicist, the same power of reproduction which we encountered when we were dealing with nerve substance, but under such far more complicated conditions. And what is known thus certainly from muscle subStance holds good with greater or less plainness for all our organs. More especially may we note the fact, that after increased use, alternated with times of repose, there accrues to the organ in all animal economy an increased power of execution with an increased power of assimilation and a gain in size.

This gain in size consists not only in the enlargement of the individual cells or fibres of which the organ is composed, but in the multiplication of their number; for when cells have grown to a certain size they give rise to others, which inherit more or less completely the qualities of those from which they came, and therefore appear to be repetitions of the same cell. This growth and multiplication of cells is only a special phase of those manifold functions which characterize organized matter, and which consist not only in what goes on within the cell substance as alterations or undulatory movement of the molecular disposition, but also in that which becomes visible outside the cells as change of shape, enlargement, or subdivision. Reproduction of performance, therefore, manifests itself to us as reproduction of the cells themselves, as may be seen most plainly in the case of plants, whose chief work consists in growth, whereas with animal organism other faculties greatly preponderate.

Let us now take a brief survey of a class of facts in the case of which we may most abundantly observe the power of memory in organized matter. We have ample evidence of the fact that characteristics of an organism may descend to offspring which the organism did not inherit, but which it acquired owing to the

special circumstances under which it lived; and that, in consequence, every organism imparts to the germ that issues from it a small heritage of acquisitions which it has added during its own lifetime to the gross inheritance of its race.

When we reflect that we are dealing with the heredity of acquired qualities which came to development in the most diverse parts of the parent organism, it must seem in a high degree mysterious how those parts can have kind of influence upon a germ which develops itself in an entirely different place. Many mystical theories have been propounded for the elucidation of this question, but the following reflections may serve to bring the cause nearer to the comprehension of the physiologist.

any

The nerve substance, in spite of its thousandfold subdivision as cells and fibres, forms, nevertheless, a united whole, which is present directly in all organsnay, as more recent histology conjectures, in each cell of the more important organs-or is at least in ready communication with them by means of the living, irritable, and therefore highly conductive substance of other cells. Through the connection thus established all organs find themselves in such a condition of more or less mutual interdependence upon one another, that events which happen to one are repeated in others, and a notification, however slight, of a vibration set up in one quarter is at once conveyed even to the farthest parts of the body. With this easy and rapid intercourse between all parts is associated the more difficult communication that goes on by way of the circulation of sap or blood.

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It is from such passages as this, and those that follow on the next few pages, that I collect the impression of Professor Hering's meaning which I have endeavoured to convey in the preceding chapter.

We see, further, that the process of the development of all germs that are marked out for independent existence causes a powerful reaction, even from the very beginning of that existence, on both the conscious and unconscious life of the whole organism. We may see this from the fact that the organ of reproduction stands in closer and more important relation to the remaining parts, and especially to the nervous system, than do the other organs; and, inversely, that both the perceived and unperceived events affecting the whole organism find a more marked response in the reproductive system

than elsewhere.

We can now see with sufficient plainness in what way the material connection is established between the acquired peculiarities of an organism, and the proclivity on the part of the germ in virtue of which it develops the special characteristics of its parent.

The microscope teaches us that no difference can be perceived between one germ and another; it cannot, however, be objected on this account that the determining cause of its ulterior development must be something immaterial, rather than the specific kind of its material constitution.

The curves and surfaces which the mathematician conceives, or finds conceivable, are more varied and infinite than the forms of animal life. Let us suppose an infinitely small segment to be taken from every possible curve; each one of these will appear as like every other as one germ is to another, yet the whole of every curve lies dormant, as it were, in each of them, and if the mathematician chooses to develop it, it will take the path indicated by the elements of each segment.

It is an error, therefore, to suppose that such fine distinctions as physiology must assume lie beyond the limits of what is conceivable by the human mind. An

infinitely small change of position on the part of a point, or in the relations of the parts of a segment of a curve to one another, suffices to alter the law of its whole path, and so in like manner an infinitely small influence exercised by the parent organism on the molecular disposition of the germ' may suffice to produce a determining effect upon its whole farther development.

What is the descent of special peculiarities but a reproduction on the part of organized matter of processes in which it once took part as a germ in the germ-containing organs of its parent, and of which it seems still to retain a recollection that reappears when time and the occasion serve, inasmuch as it responds to the same or like stimuli in a like way to that in which the parent organism responded, of which it was once part, and in the events of whose history it was itself also an accomplice?? When an action through long habit or continual practice has become so much a second nature to any organization that its effects will penetrate, though ever so faintly, into the germ that lies within it, and when this last comes to find itself in a new sphere, to extend itself, and develop into a new creature-(the individual parts of which are still always the creature itself and flesh of its

'That is to say, "an infinitely small change in the kind of vibration communicated from the parent to the germ.”

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It may be asked what is meant by "responding." I may repeat that I understand Professor Hering to mean that there exists in the offspring certain vibrations, which are many of them too faint to upset equilibrium and thus generate action, until they receive an accession of force from without by the running into them of vibrations of similar characteristics to their own, which last vibrations have been set up by exterior objects. On this they become strong enough to generate that corporeal earthquake which we call action.

This may be true or not, but it is at any rate intelligible; whereas much that is written about "fraying channels" raises no definite ideas in the mind.

flesh, so that what is reproduced is the same being as that in company with which the germ once lived, and of which it was once actually a part)-all this is as wonderful as when a grey-haired man remembers the events of his own childhood; but it is not more so. Whether we say that the same organized substance is again reproducing its past experience, or whether we prefer to hold that an offshoot or part of the original substance has waxed and developed itself since separation from the parent stock, it is plain that this will constitute a difference of degree, not kind.

When we reflect upon the fact that unimportant acquired characteristics can be reproduced in offspring, we are apt to forget that offspring is only a full-sized reproduction of the parent-a reproduction, moreover, that goes as far as possible into detail. We are so accustomed to consider family resemblance a matter of course, that we are sometimes surprised when a child is in some respect unlike its parent; surely, however, the infinite number of points in respect of which parents and children resemble one another is a more reasonable ground for our surprise.

But if the substance of the germ can reproduce characteristics acquired by the parent during its single life, how much more will it not be able to reproduce those that were congenital to the parent, and which have happened through countless generations to the organized matter of which the germ of to-day is a fragment? We cannot wonder that action already taken on innumerable past occasions by organized matter is more deeply impressed upon the recollection of the germ to which it gives rise than action taken once only during a single lifetime.1

'I interpret this, "We cannot wonder if often-repeated vibrations gather strength, and become at once more lasting and requiring less accession of vibration from without, in order to become Strong enough to generate action."