Biology

The biology of the first third of the nineteenth century was closely connected on the one hand with human physiology and medicine, and on the other with the geology of the earth. In the middle of the century both of these lines of development were brought to the support of the doctrine of evolution.

At the very beginning of the century Bichat (1771-1802) developed his theory that the body is made up of many tissues, but that the nature of each tissue remains constant and that as a consequence a disease is more liable to spread to many organs following the same tissue than throughout one organ affecting all its different tissues.

At the same time Edward Jenner (1749-1823) was industriously spreading his ideas on the subject of vaccination for small-pox. His theory was that those who had had cow-pox did not have small-pox, and that as the first was never fatal, while one out of ten to fourteen of all deaths were caused by small-pox, it would be much better to give a person cow-pox to make him immune from small-pox. His theory has been fiercely attacked, but it is certainly true that since its general application there have been no such general ravages of the disease as were formerly common, and instead of being largely fatal, the disease is now usually mild.

In 1821 Sir Charles Bell gave to the world his theory of the "nervous circle." He distinguished carefully between motor and sensory nerves, and showed that they must always go in pairs, so that the sensory nerve may keep us informed of the condition of a muscle as the data for its movement by means of an impulse sent along the motor nerve.

The next great advance in biology; was made by Karl von Baer. Karl Ernst von Baer was born in Esthonia, Germany, in 1792. He studied at Wurzburg and there began his investigations into the development of the chick and continued them while professor at Königsburg.

In 1828 he published the result of his observations. This was practically the beginning of embryology. He discovered that the embryos of different species and orders are practically alike at the beginning, that it is only after a time in their development that they leave the common road, as it were. Thus the fish would start off on a path of its own in its development first, then the reptile, then the bird, then the mammal. Thus the bird and the mammal follow the same course in their development up to a certain point. As von Baer said, "Perhaps all animals are alike, and nothing but hollow globes at their earliest developmental beginning. The farther back we trace their development, the more resemblance we find in the most different creatures. And this leads to the question whether at the beginning of their development all animals are essentially alike, and referable to one common ancestral form. Considering that the ’germ’ (which at a certain stage appears in the shape of a hollow globe or bag) is the undeveloped animal itself, we are not without reason for assuming that the common fundamental form is that of a simple vesicle, from which every animal is evolved, not only theoretically, but historically."

It must be remembered that this statement was made ten years before the discovery of the cells.

From this thought grew the principle that the history of the individual follows the history of the race, and that the history of the race is summarized in the development of its embryo. This is one of the greatest supports of the doctrine of evolution.

In the field of geology this idea of evolution began to make its appearance even before the first of the century, although it was scoffed at by almost everyone until the time of Darwin.

As early as 1790 the great German poet Goethe (1749-1833) showed that the stamens and pistils are only different transformations of the leaves of the flower, and that in fact all parts of the plant are but transformations of the stem and leaves.

In the first part of the century geological thought was led by Lamarck, Cuvier and St. Hilaire, all of them professors at the Museum of Natural History in Paris. In 1801 Lamarck (1744-1829) attacked the permanence and separate creation of species, believing that theyevolved from similar forms. The only explanation he could give was the inheritance of acquired characteristics. This explanation at times becomes ridiculous, and the theory was rather a laughing stock.

His friend Cuvier (1769-1832) was strongly against it. Cuvier emphasized the mutual dependence of the parts of any animal on one another; so much so that from a single fragment he could build up the whole specimen. He gave a wonderful proof of this fact in 1812. A large number of mysterious bones was being dug up around Paris. Cuvier collected them into a great mass and made a careful study of them upon this principle. "At the word of comparative anatomy," he wrote, "each be, no, each fragment, regained its place. I cannot describe the joy I felt in finding that, as I discovered one character, all its consequences were gradually brought to light; the feet agreed with the history told by the teeth; the bones of the legs and thighs, and those parts which ought to unite them, agreed with each other. In a word, each one of the species sprang from its own fragments." And—wonderful climax!—the complete specimens were not those of species in existence. He had resurrected a large number of extinct species. The study of such fossils thus begun by Cuvier later became one of the greatest means of attack against the very idea of the special creation of each species for which Cuvier stands.

St. Hilaire (17721844), the third of the friends, emphasized a truth complementary to Cuvier’s belief in the mutual dependence of parts, that is, that all species have the same general plan, and that the differing parts are only special modifications. "Nature," he said, "has formed all living beings on one plan, essentially the same in principle, but varied in a thousand ways in all the minor parts; all the differences are only a complication and modification of the same organs."

These two theories drew the attention of Europe even in the midst of the Napoleonic wars. They were both, although seemingly opposed, supported with apparently irrefutable arguments. This is because, as was afterwards shown by the doctrine of evolution, it is possible for both ideas to be true.

In 1830 Sir Charles Lyell in England added another great truth to those that were slowly making for some sort of an evolutionary hypothesis. He taught that the whole condition of the earth is the result only of the natural forces that are now at work upon it. He was a great friend of Spencer and Darwin, and may be said with them to be one of the founders of the great theory that marks the second third of the century. This must be left to the succeeding volume.