There is said to exist a constant, unappeasable warfare between science and religion. Perhaps it does exist, but surely only in the narrow minds of the lesser lights. In no century has science developed as in the one that has just closed. Faraday the great scientific mind of the beginning of the century, said, at one of his lectures before the Royal Academy of Sciences of England, when the century was scarcely a decade old: "I do not name God here because I am lecturing on experimental science. But the notion of respect for God comes to my mind by ways as sure as those [{296}] which lead us to physical truth." At the end of the century the monument of a great man of science is a chapel with an altar on which the sacrifice of Him that died for men is commemorated on Pasteur anniversaries.
The walls of the chapel are inscribed with the scientific triumphs of the master whose ashes repose here. It is a striking catalogue. Each heading represents a great step forward in science:
1848, Molecular Dissymmetry.
1857, Fermentations.
1862, So-called Spontaneous Generation.
1863, Studies in Wine.
1865, Diseases of Silk Worms.
1871, Studies in Beer.
1877, Virulent Microbic Diseases.
1880, Vaccinating Viruses.
1885, Prophylaxis of Rabies.
Apparently these various subjects are widely separated from one another. It might seem that Pasteur was an erratic genius. As a matter of fact, each successive subject follows its predecessor by a rigid logic. Pasteur's life-work can be best studied by a consideration of these various topics and an appreciation of the advance made in each one.
Pasteur was first of all and always a chemist! He was interested in chemistry from his early years. In the decade from 1840 to 1850 organic chemistry--or as we prefer to call it now, the chemistry of the carbon compounds--was just opening up. Great discoveries were possible as they were not before or since. Pasteur, with a devotion to experimental work that amounted to a passion, was a pupil at the Ecole Normale, in Paris. Bruited about he heard all the suggestive questions that were insoluble problems even to the great men around him. He was especially interested in the burning [{297}] question of the day, the internal constitution of molecules and the arrangement of atoms in substances which, though they are composed of exactly the same constituents, exhibit very different physical and chemical qualities. The subject is, almost needless to say, a basic problem in chemistry and remains to our own day the most attractive of scientific mysteries.
Mitscherlich, one of the greatest chemists of the time, had just announced that certain salts--the tartrates and paratartrates of soda and ammonia--"had the same chemical composition, the same crystalline form, the same angles in the crystalline condition, the same specific weight, the same double refraction and, consequently, the same inclination of the optic axes. Notwithstanding all these points of similarity, if the tartrate is dissolved in water it causes the plane of polarized light to rotate while the paratartrate exerts no such action." Pasteur could not believe that all the chemical and physical qualities of two substances could be identical and their action to polarized light be so different. Mitscherlich was known, however, as an extremely careful observer. For several years Pasteur revolved all the possibilities in Mitscherlich's observations and, finally, came to the conclusion that there perhaps existed in the paratartrates, as prepared by Mitscherlich, two different groups of crystals, the members of one of which turned the plane of polarization to the right, the other to the left. These two effects neutralized each other and apparently the paratartrates have no influence on the polarized beam of light.
Pasteur found that the paratartrates were composed of crystals that were dissymmetrical--that is, whose image reflected in a mirror cannot be superposed on the crystal itself. This idea Pasteur makes clear by reference to the mirrored image of a hand. The image of the right hand as [{298}] seen in a mirror is a left hand. It cannot be superposed on the hand of which it is the reflection any more than the left hand can be superposed on the right and have corresponding parts occupy corresponding places. Pasteur found that the paratartrates were not only dissymmetrical, but that they possessed two forms of dissymmetry. The mirrored image of some of the crystals could be superposed on certain of the other crystals just as the mirror image of the right hand can be superposed on the actual left hand. He concluded that if he separated these two groups from each other he would have two very different substances, and so the mystery propounded by Mitscherlich would be solved.
With Pasteur to conceive an idea was to think out its experimental demonstration. He manufactured the paratartrates according to the directions given by Mitscherlich, and then proceeded to sort the two varieties of crystals by hand. It was slow, patient work, and for hours Pasteur strove feverishly on alone in the laboratory. At length, the crystals were ready for solution and examination as to their effect upon polarized light. If Pasteur's idea as to the dissymmetry of crystals were confirmed, a great scientific advance was assured. Tremblingly the young enthusiast adjusted his polariscope. He tells the story himself of his first hesitant glance. But hesitation was changed to triumph. His prevision was correct. There were two forms of crystals with different effects on polarized light in Mitscherlich's supposed simple substance. Pasteur could not stay to put his instrument away. The air of the laboratory had become oppressive to him. Drunk with the wine of discovery, as a French biographer remarks, he rushed into the open air and almost staggered into the arms of a friend who was passing. "Ah," he said, "I have just made a great discovery. Come to the Luxembourg garden and I will tell you all about [{299}] it." It was characteristic of the man all through life to have no doubt of the true significance of his work. He was sure of each step in the demonstration and his conclusions were beyond doubt.
Pasteur's discovery made a profound sensation. The French Academy of Sciences at once proceeded to its investigation. Among the members who were intensely interested, some bore names that now belong to universal science--Arago, Biot, Dumas, De Senarmont. Pasteur told long years afterward of Biot's emotion when the facts were visibly demonstrated to him. Greatly moved, the distinguished old man took the young man's arm and, trembling, said: "My dear child, I have loved science so well that this makes my heart beat." How deeply these men were bound up in their work! How richly they were rewarded for their devotion to science! There were giants in those days.
Pasteur's discovery was much more than a new fact in chemistry and physics. It was the foundation-stone that was to support the new science of stereochemistry--the study of the physiochemical arrangement of atoms within the molecule--that took its rise a few years later. Much more, it was a great landmark in biology. Pasteur pointed out that all mineral substances--that is, all the natural products not due to living energy--have a superposable image and are, therefore, not dissymmetrical. All the products of vegetable and animal life are dissymmetrical. All these latter substances turn the plane of polarization. This is the great fundamental distinction between organic and inorganic substances--the only one that has endured thus far in the advance of science. Dissymmetry probably represents some essential manifestation of vital force. Often there seem to be exceptions to this law; but careful analysis of the conditions of the problem shows that they are not real.