ing a centimeter up the tube lifts a weight of nearly 1,000 grams through 1 centimeter, for the pressure of the atmostphere on a square centimeter of surface is nearly 1,000 grams-that is, it does 1,000 units of work, or ergs. So the work done by a gas in expanding is measured by the change of volume multiplied by the pressure. On the figure, the change of volume is measured horizontally, the change of pressure vertically. Hence the work done is equivalent to the area A B C D on the figure.

If liquid as it exists at A change to gas as it -exists at B, the substance changes its volume and may be made to do work. This is familiar in the steam engine, where work is done by water expanding . to steam and so increasing its volume. The pressure does not alter during this change of volume if sufficient heat be supplied; hence the work done during such a change is given by the rectangular area.

Suppose that a man is conveying a trunk up to the first story of a house; he may do it in two (or, perhaps, a greater number of) ways. He may put a ladder up to the drawing-room window, shoulder his trunk, and deposit it directly on the first floor; or he may go down the area stairs, pass through the kitchen, up the kitchen stairs, up the first flight, up the second flight, and down again to the first story. The end result is the same; and he does the same amount of work in both cases so far as conveying the weight to a given height is concerned, because in going down stairs he has actually allowed work to be done on him by the descent of the weight.

Now, the liquid in expanding to gas begins at a definite volume; it evaporates gradually to gas without altering pressure, heat being, of course, communicated to it during the change, else it would cool itself; and it finally ends as gas. It increases its volume by a definite amount at a definite pressure, and so does a definite amount of work. This work might be utilized in driving an engine.

But if it pass continuously from liquid to gas, the starting point and the end point are both the same as before. An equal amount of work has been done: but it has been done by going down the area stair (as it were), and over the round I described before.

It is clear that a less amount of work has been done on the left-hand side of the figure than was done before, and a greater amount on the right-hand side; and if I have made my meaning clear you will see that as much less has been done on the one side as more has been done on the other-that is, that the area of the figure B E H must be equal to that of the figure A FH. Dr. Young and I have tried this experimentally-that is, by measuring the calculated areas--and we found them to be equal.

This can be shown to you easily by a simple device, namely, taking them out and weighing them. As this diagram is an exact representation of the results of our experiments with ether the device can be put in practice. We can detach these areas, which are cut out in tin,

and place one in each of this pair of scales and they balance. The fact that a number of areas thus measured gave the theoretical results of itself furnishes a strong support of the justice of the conclusions we drew as regards the forms of these curves.

To attempt to explain the reasons of this behavior would take more time than can be given to-night; moreover, to tell the truth, we do not know them. But we have at least partial knowledge and we may hope that investigations at present being carried out by Prof. Tait may give us a clear idea of the nature of the matter and of the forces which act on it, and with which it acts, during the continuous change from gas to liquid.

PRESENT PROBLEMS IN EVOLUTION AND HEREDITY.*

By HENRY FAIRFIELD OSBORN.

In the past decade of practical research and speculation in biology, two subjects have oustripped in interest and importance the rapid progress all along the line. These are, first, the life history of the reproductive cell from its infancy in the ovum onward, and second, the associated problem of heredity, which passes insensibly from the field of direct observation into the region of pure speculation.

As regards the cell it was generally believed that the nucleus was an arcanum into the mysteries of which we could not far penetrate; but this belief has long been dispelled by the eager specialist, and it is no exaggeration to say that we now know more about the meaning of the nucleus than we did about the entire cell a few years ago. At that time the current solution of the heredity problem was a purely formal one; it came to the main barrier, namely, the relation of heredity and evolution to the reproductive cells, and leapt over it by the postulate of Pangenesis. The germ-cell studies of Balfour, Van Beneden, the Hertwig brothers, Weismann, Boveri, and others, have gradually led us to hope that we shall some day trace the connection between the intricate metamorphoses in these cells and the external phenomena of heredity, and more than this, to realize that the heredity theory of the future must rest upon a far more exact knowledge than we enjoy at present of the history of the reproductive cell both in itself and in the influence which the surrounding body cells have upon it.

These advances affect the problem of life and protoplasm, whether studied by the physician, the anthropologist, or the zoologist, thus concentrating into one focus opinions which have been formed by the observation of widely different classes of facts. As each class of facts bears to the observer a different aspect and gives him a personal bias, the discusson is by no means irenical, and it is our privilege to live through one of those heated periods which mark the course of every revolution in the world of ideas. Such a crisis was brought about by

*The Cartwright Lectures for 1892; delivered before Alumni of the College of Physicians and Surgeons, February 12, 19, and 26, 1892. (From the Medical Record for February 20, March 5, April 23, and May 14, 1892.)

the publication of the theory of Darwin, in 1858, and, after subsiding, has again been aroused by Weismann's theory of heredity, published in 1883.

This is the situation I have ventured to present to you as Cartwright lecturer, not, of course, without introducing some conclusions of my own, which have been derived from vertebrate palæontology, but which I shall direct mainly upon human evolution.

So far as theories need come before us now, remember that Lamarck (1792) attributed evolution to the hereditary transmission to offspring of changes (acquired variations) caused by environment and habit in the parent. Darwin's latest view was that evolution is due to the natural selection of such congenital variations as favored survival, supplemented by the transmission of acquired variations. Weismann denies the transmission of acquired variations, or characters, entirely, and attributes evolution solely to the natural selection of the individuals which bear the most favorable variations of the germ or reproductive cells. We must therefore clearly distinguish between “congenital variations" which are part of our inheritance and “acquired variations” which are due to our life habits; the question is, are the latter transmitted?

At the outset I would emphasize the extreme complexity of evolution by a few words upon variation, or in terms of medical science, upon anomalies.

When we speak of a part as "anomalous" we mean that it varies at birth from the ordinary or typical form; it may be minute, as the small slip of a tendon, or large, as the addition of a complete vertebra to the spinal column. Wood has found that in the muscular system alone there are nine anomalies in the average individual. It is clear that the evolution of a new type, so far as the muscular system is concerned, must consist in the accumulation of anomalies in a certain definite direction by heredity. Thus the anomalous condition of one generation may become the typical condition of a very much later generation, and we observe the paradox of a typical structure becoming an anomaly and an anomalous structure becoming typical; for example, the supracondylar foramen of the humerus was once typical, it is now anomalous; the retardation in development of the wisdom tooth was once anomalous, it is now typical.

The same principle applies to races which are in different stages of evolution; an anomaly in the white, such as the early closure of the cranial sutures, is normal in the black. Now the deductions of the Weismann school of evolutionists seem to be founded upon the principle "de minimis non curat lex;" that we need only regard such major variations as can, er hypothesi, weigh in the scale of survival. Against this I urge that we must regard the evolution of particular structures, the components of larger organs, the separate muscles and bones for example, for the very reason that while in some cases they play a most

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humble rôle in our economy we can prove beyond a doubt that they are in course of evolution. Minor variations in foot structure, which are possibly of vital importance to a quadruped whose very existence may depend upon speed, sink into obscurity as factors in the survival of the modern American.

The evolution of man in the most unimportant details of his structure promises, therefore, to afford a far more crucial test of the Lamarckian vs. the pure natural selection theory, than in the domain of his higher faculties, for the reason that selection may operate upon variations in mind, while it taxes our credulity to believe it can operate upon variations in muscle and bone. This is my ground for selecting the skele ton and muscles for the subject of the introductory lecture. Nevertheless, let us review variation in all its forms in human anatomy before forming an opinion. Let us remember, too, that congenital and acquired variations are universal as necessities of birth and life; they are exhibited in the body as a whole-in its proportions, in the components of each limb, finally in the separate parts of each component, as in the divisions of a complex muscle. Thus the possibilities of transformism are everywhere. What is the nature and origin of congenital variations? Their causes? Do they follow certain directions? Do they spring from acquired variations by heredity? These are some of the questions which are still unsettled.

But striking as are the anomalies from type, the repetitions of type as exhibited in atavism and normal inheritance are still more so, aud equally difficult to explain. Therefore our theory must provide both for the observed laws of repetition of ancestral form and the laws of variation from ancestral form, as the pasture-land of evolution. Add to these, that for a period in each generation this entire legislation of nature is compressed into the tiny nucleus of the fertilized ovum, and the whole problem rises before us in its apparent impregnability which only intensifies our ardor of research.

LECTURE I.-THE CONTEMPORARY EVOLUTION OF MAN.

The anthropologists and anatomists have enjoyed a certain monopoly of Homo sapiens, while the biologists have directed their energies mainly upon the lower creation. But under the inspiring influences of the Darwinian theory these originally distinct branches have converged, and as man takes his place in the zoological system, comparative anatomy is recognized as the infallible key to human anatomy.

For our present purpose we must suppress our sentiment at the outset and state plainly that the only interpretation of our bodily structure lies in the theory of our descent from some early member of the primates, such as may have given rise also to the living Anthropoidea. This is also the only tenable teleological view, for many of our inherited organs are at present non-purposive, in some cases even harmful,— as the appendix vermiformis,