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man's comfort and health, during my lifetime have been marvellous.

The shrill whistle of the locomotive had been barely heard before 1837, but few there were who foresaw what a revolution in transportation and in industry steam was to produce. Steamships, depending wholly on steam, first ventured across the Atlantic when I was a year old.

The early staccato of the telegraph had also made itself heard, but its future growth and possibilities on land, and under the sea, and in the air could not have been even imagined.

The typewriter, the telephone and the automobile have tripled the efficiency of the doctor. Possibly the airplane in time may quadruple it.

May I venture here to digress for a moment to let you enjoy the recent experience of one of my London scientific friends. In writing a letter he dictated to his secretary, an ardent suffragette, the phase, "When Plancus was Consul," alluding to the friend of Horace to whom he addresses the seventh in the first What was his amazement book of his Odes. to read in the letter presented for his signature, "When Pankhurst was Consul." He was so appreciative of the joy that this variant reading would give his friend, that he signed the letter unchanged.

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Science has progressed by leaps and bounds. "The most fruitful periods of Science," says Duclaux, in his recent Life of Pasteur, those in which dogmas are shaken," that is to say when every postulate is ruthlessly reexamined. This "shaking of dogmas" has given us radio-activity, and has divided the "atom"-that supposed ultimate particle of matter, whose very name means "indivisible" -in some cases into hundreds of electrons.

By the Spectroscope which, in my university days at Brown, existed only in embryo as the curious "Fraunhofer lines" of the solar spectrum, we now analyze the chemical elements of suns many millions of times larger than our own and so distant that the light now reaching our eyes from them started on its earthward journey hundreds of thousands

of years ago. Even light itself has measured and weighed, and Einstein's lation of the doctrine of relativity i claimed as the most fundamental dis since the days of Sir Isaac Newton.

elec In 1876, scarcely 45 years ago, had progressed but little beyond the where Franklin had left it at the time death in 1790, just eighty-six years bef Centennial Exposition. Now, the sloga it is not electric, it is not modern" is literally true.

At the Centennial Exposition, moder tricity was represented by Professor F one arc light on the roof of the main of a might ing, the "avant courier The dynamo-appropriately named. Force, Power-had been slowly develop the brains of Faraday and his suc Within the last two score years, tha has been harnessed and has becor obedient slave in heat, light and pow land and on sea, in mine and in m fact, the catalogue of the things t dynamo can not as yet do would be than the things it is actually doingend is not even yet in sight.

My professional life covers sixty-on of study, active practise, writing and ing. At its very outset occurred th fortunate event in my professional life under the spell of Dr. S. Weir Mitc have met many eminent medical men : and abroad, but I do not hesitate to s he was by far the most alert, origin stimulating mind with which I ha been in contact. I have often called "yeasty man " for he leavened and fermentation every mind which touc own. He gave me my first scientific and set congenial tasks for my mind a For over 53 years we worked toge many activities of the profession, wit a cloud between us.

Close upon making his acquaintan the Civil War. By a curious acciden came an assistant surgeon in the A

1 Keen's "Addresses and Other Papers,

July 1, 1861, before I was a graduate in medicine. I knew but little medicine but I replaced a predecessor who demonstrably knew still less, for, at the end of my first year, I coached him for graduation at the end of his second year. I am in doubt whether I ought to be commended or condemned for the result, for he actually succeeded in achieving his diploma.

As to myself, my very ignorance was a safeguard to those under my care for I was inidsposed to take any serious risk by heroic treatment. After this service with a regiment of "three months' men," we were honorably discharged August 1, 1861. I then completed my studies and obtained my M.D. in March, 1862. After a real examination, I reentered the service, fortunately for me not in the regulars to which I was entitled, but as an Acting Assistant Surgeon.

Again Mitchell's inspiring touch was vouchsafed to me. At his request, I was assigned, by Surgeon General Hammond, to the neurological ward under Mitchell and Morehouse. I became the junior in what might be called a neurological "firm." "Mitchell, Morehouse & Keen" became very widely known to the profession because Mitchell made it so. His generosity to me when my diploma was hardly dry, in associating my name with his own, already widely known as that of a distinguished physiologist, was as fortunate for me as it was generous upon his part. Our studies, especially in the Turner's Lane Hospital, Philadelphia, laid the foundations of modern Neurological Surgery.

Returning from study in Europe in 1866, I took over the Philadelphia School of Anatomy -founded by Lawrence in 1820-and taught anatomy and operative surgery to large private olasses of medical students (1866-1875) when the government took the property for the use of the present postoffice.

From 1866 to 1875, I taught surgical pathology in the Jefferson Medical College. In doing this, I learned ten times as much as my most studious pupil. From 1876 to 1890, I lectured on artistic anatomy in the Pennsylvania Academy of the Fine Arts.

From 1884 to 1889, I was professor of surgery at the Women's Medical College, and from 1889 to 1907, I was professor of surgery in the Jefferson Medical College, a total service as a teacher of 41 years (1866-1907). No one, not himself a teacher, can imagine the joy of that long service. To meet daily scores of earnest, alert minds, greedy for knowledge, was a daily inspiration and developed the most intense desire to give of one's very best.

In 1901-02, with two of my daughters, I made a tour around the world. We penetrated into Java and beyond the Caspian into Turkestan, almost to the western border of China. It is no wonder that, having taught many thousands of students, I was heartily welcomed by some of them in country after country. From the Golden Gate, all the way to Russia, traveling over westward, in Hawaii, Japan, China, the Philippines, India, Egypt, Greece and Palestine, in every land save Java and Turkestan, I had old students. In Korea, also, several were and still are doing splendid service as medical missionaries and others again as teachers in the Medical College in Siam. Even in Persia, there was one-a Persian who returned to his native land as a Christian Medical Missionary. Early in the World War, when the Turks captured Urumiah, where he was dispensing health and happiness to his fellow countrymen, they seized him and gave him the fearful choiceMohammedanism or the stake and Joseph Shimoon, the martyr, was burned alive for his faith, by the unspeakable Turk!

The nine epoch-making medical events in the last century and a quarter are:

1. Vaccination against smallpox (1796). 2. Anesthesia (1846).

3. Pasteur's researches were the foundation of the new science of bacteriology (1850 to 1884).

4. Pasteur's chief claim to fame is his further and "fundamental discoveries in immunology, or the science of the specific prevention of disease" (Flexner).

5. Pasteur's and Lister's researches resulting in antiseptic and aseptic surgery and obstetrics.

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6. The discovery that insects carry disease (1889).

7. The discovery of radio-activity and especially for medical use, the X-rays (1895). 8. The development of a medical literature written by American authors (18591920).

9. The founding of great laboratories of research.

With the exception of the first, every one of these wonderful discoveries has occurred during my own lifetime.

The first research laboratory was founded in 1884 by Andrew Carnegie, in connection with the Bellevue Hospital Medical College in New York. Others, larger and more elaborate, soon followed, usually in connection with other medical schools. The greatest and most useful of them all is the wonderful Rockefeller Institute for Medical Research, an independent institution in New York City. From that busy center has come one beneficent discovery after another, the last being the discovery by that remarkable genius, Hideyo Noguchi, of the germ of yellow fever, and the preparation of a vaccine which in case of exposure, has proved to be not only a means of protecting those who have never had an attack, but to be actually curative of the fever if administered very early.

In my student days, practically all of our important medical text books were of European, and especially of British origin. The sole exception was the elder Gross's two-volume Surgery (1859) and, twenty years later, Agnew's Surgery in three volumes. Now, there is hardly any department of medicine in which there are not several American text-books of great merit, and our medical journals rival those of Europe.

The first text-book of Surgery in the English language, founded upon bacteriology, the corner stone of modern surgery, was the "American Text-book of Surgery," which I organized, and later, with the assistance of Dr. J. William White, as co-editor, and eleven other American surgeons-published in 1892. It passed through four large editions. I have just finished a still larger work by about 100

American and British authors in eigh
It to
umes, averaging 1,000 pages each.
years of labor ere I could write "Fini
1921 was ushered in.

Every intelligent person knows of th
tual revolution in surgery, medicine,
rics and all the specialties, which has
Anesthesia has
place of late years.
surgical operations of nearly all their
Antiseptic, and later, aseptic methods,
made the old operations safe, as shown
unparalleled diminution of the mortalit
has made possible, also, a vast numb
operations which were absolutely prohibi
the first twenty years of my professiona
because of their fatality. "Noli me tan
was writ large on the head, the chest a
abdomen. To-day, we invade these
sacrosanct cavities with a free hand an
glorious life-saving results.

Medicine has progressed equally far know the causes of various diseases, wh were fighting in the dark until bacteriol vealed to us the realm of the almost in little, but they put the multiplication t shame by the incredible rapidity of growth. It is Lilliput versus Gulliver. • Medical science, however, girded up it in our laboratories of research and at t side, and resolutely attacked the enem has won victory after victory. We soon not only the cause but the mode of mission of these various diseases, especia remarkable discovery that insects-th quito, the louse, the tick, the flea and -and some of the lower animals, especia dog and the rat, were the means of sp disease.

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The results of these combined eries are seen in the imminent bani from the whole earth of yellow fev immense diminution of typhoid, tetanus theria and other germ diseases, and th ing of tuberculosis and other diseases, b of course, the results of the war.

Maternity, which nature surely inter be a normal and a safe physiological was very dangerous for years after I ated. The usual death rate in the '6

'70's

's was from three to five mothers in every hundred, and sometimes childbed fever raged in epidemic form and killed at the rate of 20, 40 and even 55 mothers in every hundred! , Now, this most beautiful of all human relations has been made safe-mark my wordsmade safe by the researches, especially of Pasteur and his successors. Bacteriology has won this splendid victory. Within the last decade, series of 6,000, 7,000 and even over 8,000 cases have been reported without the death of a single mother from infection. Is not that a cause for a Te Deum?

But I must call a halt though I have not told even a small fraction of the fascinating story, of what, remember, I have been an enthusiastic living witness.

And what of the future? Have we any reason to expect other astonishing and beneficent discoveries? I answer with an unqualified affirmative. And it may well be still greater and still more beneficent discoveries.

With this word of cheer, I face the coming year or, if it so please God, the coming years, with a confidence which is enhanced by your wonderful tribute of affection.

THE RELATION OF MENDELISM AND THE MUTATION THEORY TO NATURAL SELECTION1

Two marked tendencies are evident in the history of any important theory after its publication.

First. The followers of the discoverer carry the theory too far and attempt too universal an application. This is manifestly true of Wallace and Weismann who out-Darwined Darwin in their claims for natural selection; of the followers of Mendel, such as Morgan and Pearl; and of many mutationists who make much greater claims for that theory than does De Vries himself.

Second. Each generation of biologists is so occupied with its own work and contemporary theories that it makes no real effort to understand preceding theories.

1 Read before the American Society of Naturalists at Chicago, December 31, 1920.

This second tendency seems to me most marked in the attitude of present workers along genetic lines towards natural selection. They reveal an apparent lack of understanding of what Darwin really meant and of what he claimed; and when criticising that theory they are often engaged in the classic, but unprofitable, exercise of "fighting windmills,"

In view of these facts I hope you will pardon me if I present in as few words as possible just what I believe to be the main factors which Darwin presented as resulting, in their actions and reactions, in natural selection. These factors are three in number: First. Heredity, by which the progeny tend to resemble their parents more than they do other individuals of the same species. Second. Individual variation, by which the progeny tend to depart from the parental type and sometimes from the specific type. Third. Geometrical ratio of increase, by which each species tends to reproduce more individuals than can survive.

Each of these factors is practically axiomatic, so little is it open to argument.

No one doubts the fact of heredity, whether pangenesis, Weismannism or Mendelism be the correct expression of the mechanism involved. These do not affect the fact of heredity nor invalidate it as a factor in natural selection.

No one doubts the fact of variation; whether it is the "individual variation" of Darwin, the "fluctuating variety" or the "mutation" of De Vries. All that is necessary for Darwin's purpose is that there be heritable variations. That there are such things all parties agree and it matters little what you call them. They are adequate to act as a factor in the Darwinian scheme.

No one doubts the fact of geometrical ratio of increase. It is a proposition easily capable of mathematical demonstration, and that it is is sufficient for Darwin's purpose.

These three factors, then, are not debatable as facts, whatever their mechanism or causes. A moment's reflection will show that geometrical ratio of increase is a quantitative factor, giving an abundance of individuals

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SCIENCE

from which to select; that individual variation is a qualitative factor, giving the differences which make a selection possible; and that heredity is a conservative factor, holding fast those characters which better fit the organism to its environment.

Now it seems to me that there is no possible outcome of the necessary action and interactions of these three factors that would not be a selection of some sort. Darwin thought it comparable in a large way to the selection by which the stock-breeder improves his herd, and therefore called it "natural selection," carefully guarding the phrase from misinterpretation from the teleological angle as well as from a too close parallelism between artificial and natural selection. And I believe no one has suggested a more acceptable term for the process of selection resulting from the interplay of natural laws.

Three outstanding theories have been advanced since the publication of the "Origin," each involving an advance in our knowledge of the mechanism of heredity on the one hand and of the origin of variations on the other. Weismann's theory of the continuity and stability of the germplasm was of immense importance in its discussion of the mechanism of heredity, and his amphimixis gave a plausible explanation of the origin of variations. His results were almost universally regarded as confirming and greatly extending the scope of natural selection.

Mendel's theory regarding the purity of the gametes, their segregation in the sex cells, and the whole complex Mendelian mechanism so admirably described by Morgan; all of these, fascinating and important as they are, deal with the mechanism rather than the fact of heredity. In my opinion their acceptance or rejection does not affect the status of natural selection as a theory of organic evolution.

But it is the theory of mutation that has furnished most of the ammunition for the opponents of natural selection; and this in spite of the fact that De Vries, the originator of the mutation theory, expresses himself with great clarity as follows:

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My work claims to be in full accord w principles laid down by Darwin and to give ough and sharp analysis to some of the i and variability, inheritance, selection which were necessarily vague in his time.

In 1904, when these words were pul there did seem to be a sharp distinct tween the ideas of Darwin and those Vries. The former believed that selection acted upon many small var and accumulated them until the diff were sufficient to constitute new species De Vries claimed that new specie formed by the sudden appearance by tions of forms specifically distinct fr parents. That mutants were new spec It seems evident that Darwin did as the c gard "saltatory evolution" method, while De Vries did.

Darwin believed that individual, small, variations furnished the mate which selection acts; while De Vries that mutants, usually large variation nished the material. Both, however, thoroughly that natural selection was causa of evolution.

But things have changed greatly sin The work of Morgan, Castle, Jenning host of others has shown that many m

are so small, from a phenotypic sta that they are quantitatively no great the individual variations of Darwin; & they are heritable in the mendelian w

Castle produced a perfectly graded hooded rats which exhibits almost ide steps by which a new form might be p by natural selection. He says:

If artificial selection can, in the brief s man's lifetime, mould a character stead particular direction, why may not natural in unlimited time also cause progressive in directions useful to the organism?

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