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One of the strongest criticisms of the experiments of Schultze and of Schwann was advanced against the use of caustic chemicals and heat in filtering the air. In a series of communications published in the "Annalen" Schröder and von Dusch described a method of filtering air through cotton-wool to remove the suspended matters. This overcame the argument that heating air or subjecting it to drastic chemical treatment had devitalized it and had removed from it some vague physicochemical catalyser which was said to be responsible for the initiation of fermentation. It was now almost certain that yeast was the cause of fermentation, and that yeast cells did not arise spontaneously in fermentations but entered from the air or were present in the fermentable liquid.

It is difficult to say just what was the status of affairs at this time, but it is certain that belief in the sponaneous generation of living things was being weakened. And in the period between 1857 and 1875 Louis Pasteur sounded the death knell of spontaneous generation. He succeeded in firmly establishing his thesis-no fermentation without life: living things, for so microscopic forms were now recognized, do multiply in the putrescible or fermentable liquid and cause putrefaction or fermentation in the course of their metabolism. Pasteur also laid the real foundations of one of the newest branches of biological science, Bacteriology, and made possible the tremendous advances which the Science of Medicine has made since he placed on a sound and accurate basis the knowledge of the etiology of infectious diseases.

In the last fifty years the advances in the biological sciences have been made at a steadily accelerating rate. Since 1898, the year in which Eduard Buchner succeeded in preparing from yeast cells a non-living substance (zymase) which ferments sugar, biologists have felt that though they could imitate the actions and reactions of living things, the question of the origin of life was probably one which they were not in position to analyze successfully. Thus it was agreed twenty years ago that living things did not appear in the manner in which the Greeks or even the Middle Age scientists had declared they did. While Huxley's dictum omne vivum ex ovo as applied to higher forms of living things had become omne vivum ex vivo and was applied to

include the lowest organisms, yet no further light had been thrown upon the origin of the first forms of life. Nor had any reason been advanced why men should not believe that living things are continuously being created in a form so simple that we do not recognize them as living organisms.

Let us turn aside now from historical treatment and consider in the first place the status of the sciences in the philosophy of life and in the second place let us attempt to attain a theory which shall at least be in harmony with established facts. It is perhaps fitting to point out that such a point of view cannot allow of agreement with all or even several of those theories which have been proposed in recent times. It may perhaps lead to some development beyond these and to a crystallization of the philosophies of others.

Since Pasteur established the true nature of microscopic forms tremendous advances have been made in all the branches of science. It is probably true that the natural philosopher of Aristotle's time would have been more at home in the scientific world of England and France in 1840 than the thinker of that date would be in our day. This statement may appear somewhat paradoxical at first sight. That it is borne out after more careful consideration may be evidenced by the great advances in recent years of chemistry, physics, experimental biology and medicine, and the border-line science of physical chemistry. No one science is attaining more interesting phases and assuming greater importance than the last named. Astronomy, geology and paleontology, too, are showing no sluggard's pace. The greatest tendency is to focus from the infinitely large to the infinitely small, and with this there has appeared a trend of interest away from the planets and solar systems down to the researches on the microscope, the molecular, the atomic, the subatomic-the electronic. How have these affected our philosophies?

Years ago attention was being brought by the earliest astronomers upon the extra-terrestrial. These pioneers met with but scant attention from the world until the churchmen recognized the danger inherent in permitting this parasite to grow. It was making people question one of the canons of the Church. It was compelling people to recognize that our earth is hardly the

centre of the universe and that if this world was created it could hardly have been prepared especially for man; scarcely with him. as its nucleus. Man, such a wee mite, was hardly a fitting ruler of the mighty expanses which the telescope was revealing. From the days of Galileo the important advances of science-important in so far as they have influenced the thoughts of mankind may be traced through the naturalists Buffon, Lamarck, Cuvier, Darwin, Huxley, Weisman, DeVries, and the physicists Van't Hoff, Helmholtz, Rutherford, Ramsay, and Thomson (Lord Kelvin). It would make too long a story to follow all the influences involved; nor is it likely that a single individual could do it. It is sufficient to point out that out of the melting pot two great conceptions of life have crystallized, the one termed the vitalistic and the other the mechanistic.

The vitalistic conception of life first considers matter on the earth as divided into two great classes, the living and the nonliving. The latter is to be distinguished from the dead and is restricted to that which existed previous to the appearance of life. It proposes that in the world of the living there are forces or energies of specific and distinctive natures. These do not appear nor have they ever existed in the realms of the nonliving. This conception necessarily precludes the origin of life on the earth and points either to the earlier existence of life on other planets and transmission to our own or to the fashioning hand of God. To the agnostical or atheistical philosopher who is seeking the origin of life, the former of these appears hopeless and pushes the answer farther away. Furthermore it does not explain how life originated on other planets. The latter, it is almost needless to say, can be accepted by inquisitive minds only as a last resort and only after every other explanation capable of proof or disproof has been exhausted.

The so-called theory of panspermia according to which lifegiving seeds are drifting about in space and are established upon planets after accidental encounters received a fresh impetus about ten years ago. As early as 1871 in a popular lecture on the growth of the planetary system Helmholtz said: "It seems to me a perfectly just scientific procedure, if we, after the failure. of all our attempts to produce organisms from lifeless matter, put the question, whether life has had a beginning at all, or whether

it is not as old as matter, and whether seeds have not been carried from one planet to another and have developed everywhere where they have fallen on a fertile soil." The only criticism which may be appended to this assertion is that it is scarcely accurate to state that many attempts to create living things have been made. Further than this, one is compelled to give the Scotch verdict, "I hae me douts." Sir William Thomson (later Lord Kelvin) presented the same conception in a modified form. He professed that there are probably many worlds besides our own and that seed-bearing meteoric stones, moving about through space, might serve to transport life.

In 1907 the great Swedish scientist Arrhenius presented his modification of the hypothesis of panspermia. He pointed out first that Lord Kelvin's views were hardly free from criticism. A "meteorite in its fall toward the earth becomes incandescent all over its surface and any seeds on it would therefore be deprived of their germinating power." In presenting a substitute for Kelvin's meteorite he points out that for particles below a certain size, the mechanical pressure produced by light waves— the radiation pressure-can overcome the attractive force of gravitation.

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“Bodies which, according to the deductions of Schwarzschild, would undergo the strongest influence of solar radiation must have a diameter of .00016 mm., supposing them to be spherical. The first question is, therefore: are there any living seeds of such extraordinary minuteness. The reply of the botanist is that the so-called permanent spores of many bacteria have a size of .003 or .002 mm., and there are, no doubt, much smaller germs which our microscopes fail to disclose. We will make a rough calculation of what would happen if such an organism were detached from the earth and pushed out into space by the radiation pressure of the sun. The organism would, first of all, have to cross the orbit of Mars; then the orbits of the smaller and of the outer planets; and having passed the last station of our solar system, the orbit of Neptune, it would drift farther into infinite space towards other solar systems. The organism would cross the orbit of Mars after twenty days, the Jupiter orbit after eighty days, and the orbit of Neptune

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after fourteen months. Our nearer solar system, Alpha Centauri, would be reached in nine thousand years.”

Inasmuch as the spores would be travelling through a medium devoid of an atmosphere and of moisture and at a temperature of about -220°C. it is not unthinkable that they could survive. The evidence from experiments with bacteria is highly reassuring.

Osborn, the great American paleontologist, has defined the mechanistic conception of life as the more modern opinion "that life arose from a recombination of forces pre-existing in the cosmos. To hold to this opinion, that life does not represent the entrance either of a new form of energy or of a new series of laws, but is simply another step in the general evolutionary process, is certainly consistent with the development of mechanics, physics, and chemistry since the time of Newton and of evolu tionary thought since Buffon, Lamarck, and Darwin." The purpose of the "mechanists" has been to demonstrate that the observable phenomena of living things can be explained on purely physical and chemical bases, without recourse to any indefinable "vital principle" or "essence of life." So successful have their efforts been that to-day it can be safely said that most scientists. are mechanists. The published books of Jacques Loeb, the foremost mechanistic biologist of the day, are perhaps the best complete presentation and have played no inconsiderable part in influencing the thoughts of the scientific world.

Until very recently the studies of the "mechanists" were centered about the chemical and chemico-physiological researches. Recently a new note has been struck and a new era in scientific thought introduced by Professor Osborn. His development of an energy conception of Evolution and Heredity opens "green fields and pastures new" but leaves much to be desired at present.

It is not by any means established to-day that the explanation of life should be sought in the physical terms of motion and matter. That Kant first adopted this view and later estranged himself from it is not at all surprising. It is exceedingly difficult for one not endowed with an over-plentiful supply of faith in the clarity of his thought not to believe that he will meet a brick wall in his search for this will-o'-the-wisp of science, when he uses physics and chemistry as his tools. To date, the farthest

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