When in 1628 Harvey discovered the circulation of the blood, physiology was almost unknown, and medicine was in the full tide of empiricism. It is well known that the Faculty of Medicine of Paris refused to believe in circulation, in spite of experiments, and that it persecuted and calumniated Harvey. "That which pleases me in my son," said Diafoirus, "and in which he follows my example, is, that he remains faithful to the opinions of our ancient teachers, and that he has always refused either to understand or to listen to the arguments and experiments of the pretended discoveries of our century, especially as regards the circulation of the blood."
The history of the discovery of germinative foliations in the embryonic development of vertebrates forms one of the most impressive of human documents. In 1700 the theory of pre-formation was vigorously upheld amongst the many ideas relating to generation: that is to say, it was believed that the germs contained little organisms completely formed which would eventually unfold and increase the parts of infinitesimal dimensions which were packed one within the other. This theory applied to every living creature, animal, vegetable, and human. It had led, by its own logical development, to the more far-reaching theory of "mutual inclusion"—that is, the doctrine that, as all living organisms are pre-formed, they must of necessity all have existed from the Creation, the one included, or wrapped up, in the other. All humanity must have lain in the ovaries of Eve. When in 1690 Leuwenhoek discovered spermatozoa by the aid of the microscope, the idea was evolved that each male cell contained a complete microscopic man, the homunculus; and then it was announced that not Eve, but Adam had contained all humanity within himself. Hence the two contradictory theories which in the eighteenth century kept their adherents sharply divided, the theories of the ovulists and those of the animalculists, and the dispute seemed to offer little hope of a possible decision. The names of famous scientists and philosophers were associated with these dissensions, those, for instance, of Spallanzani and of Liebnitz, who applied the principles of generation even to the soul. "Thus I should think," said Liebnitz, "that the souls which will one day become human souls, were present in the germ; that they have always existed as organized bodies in their progenitors from Adam onwards—that is, from the beginning of things." [8]
Haller, the ovulist, who had great authority as a physiologist, in a famous work, Elementa physiologiae, upheld the principle vigorously: "Nulla est epigenesis. Nulla in corpore animale pars ante aliam facta est et omnes simul creatae existunt" (nothing is created anew, no part of the human body is made before any other part, all are created at the same time). Making a calculation based on Biblical cosmogony of the number of human beings who were packed in the ovaries of Eve, he reckons them at two hundred thousand millions. Such was the state of thought when in 1759 K. F. Wolff published some of his studies in the work Theoria generationis, where he maintained, on the strength of experiments and microscopic observations made on the embryos of fowls, that new organisms are not pre-formed, but that they create themselves entirely, starting from nothing—that is, from a microscopic cell, simple as are all primitive cells. He described the simple process by which the real evolution of individuals is brought about: from a single cell, by division, two, and then four and then eight, are formed, and so on. And the cells thus germinated divide themselves into two or three tiny folds of "primitive folioles" from which all the organs are evolved, beginning with the alimentary canal. "This assertion," says Wolff "is not a fanciful theory; it is a description of facts collected by means of the most trustworthy observations."
All the scientists of his day knew and made use of the microscope; all might have taken an egg, that is, the embryo of a fowl, as a subject for observation; they were not indifferent to the problem of individual genesis, but in their case it had merely excited the most complex efforts of the imagination, and had divided them into factions, as adversaries in a battle of thought. Could any one of them attempt to experiment and observe save at the risk of destroying himself together with his adversaries, as Samson destroyed himself with the Philistines? The possibility that there might be some truth in what had been seen and described, and that it might recur, should indeed have induced some one to venture upon a road which, if it proved to be the right one, would have been a glorious path to a future of discoveries and distinctions. But no. A dense fog obscured all minds, and the dazzling truth could not pierce it; thus all progress in embryology was precluded.
Fifty years had passed, and Wolff, poor and persecuted, had died at Petrograd, an exile from his native land, when Pander and Ernest von Baer grappled anew with the theory of "blastodermic foliation." Then the scientific world perceived the truth and accepted the evidence, inaugurating those studies in embryology which shed so much luster on the nineteenth century.
Why was it necessary that fifty years should elapse before men could see what was evident? What had happened in these fifty years? The work of Wolff, dead and forgotten, can have had no influence whatever. The fact was merely that men saw subsequently what it had been previously impossible for them to see. A kind of internal maturity must have come about in them, by virtue of which their spiritual eyes were opened, and they saw. When those eyes were closed, evidence was useless. Fifty years earlier, a direct attack would have spent itself on insuperable obstacles; but with the lapse of time the subject presented itself, and was simply and universally accepted, not only without a struggle, but without any excitement.
This fact might be arguable in relation to the internal maturation of the masses; but it is beyond question in its relation to the individual. When an obvious truth cannot be seen, we must retire, and leave the individual to mature. A struggle "to bring about perception of evidence" would be bitter and exhausting. But when maturity comes, we shall find the seer filled with enthusiasm, and bearing fruit like the vines of the Land of Promise.
When in 1859 Charles Darwin expounded the theory of evolution in his book, "The Origin of Species," he recognized the great influence it had had upon the thought of his day, for he wrote in his note-book: "My theory will lead to a philosophy." His conception of the struggle for life and of the natural selection of characteristics, so widely adopted by the thinkers of his day, popularized the principles of Lamarck as to the casual formation of new characteristics in a species by adaptation to environment; Darwin's conception carried these principles along with it—and almost fused them in its own content. These principles, excluding both creation and its finalities, implicitly denied the immortality of the soul. The effect of such a revolution may be imagined; for many centuries the soul had been the object of life, and when the fundamental faith of existence was shaken, the life of the conscience itself was convulsed. It may be supposed that there was an anxious search for contradictions in the destructive theory, if on no other grounds than that of the instinct to preserve ancient beliefs, which lies deeply rooted in the human race.
But let us take into consideration the two revolutionary principles which so greatly impressed and fired the consciousness of the university students of several generations. One principle was: "There can be no function without an organ." The other principle which created much enthusiasm among studious youths was: "The function creates the organ." What! There is no function without an organ, nor can the function even exist without the organ; and yet, on the other hand, the function without the organ can exist so vigorously as to create? No such glaring and tangible contradiction had ever existed in any theory.