of disease, and promulgated that doctrine, so bold for his time, "Omnis cellula ab cellula" (every cell from a cell)—a doctrine that will always stand like a corner stone of the temple of science. The continuity of everything living expressed by this doctrine was confirmed later on by the progress made in comparative anatomy, so that the fundamental plan common to the type of vertebrates could be traced to its last details, and it was shown that between animal and human structure the characteristic of distinction is not absolute, but only relative. Of special importance in this connection is the proof that even the organ of mind—i. e., the brain—is no exception to the general rule, and that it is built on a common fundamental plan in both man and animal.
After all, not much had been gained for a philosophical view of Nature and a natural explanation of generation, in its inception, by the discovery of the cell as the primordial form of the organic world, the cell itself being too high and complicated a formation to be regarded as rudimentary. There was therefore a hiatus in our knowledge which gave the opponents of the theory that the world is the result of a series of changes governed by natural laws a convenient ground for declaring the theory untenable and false. But this difficulty also was removed by the discovery (likewise belonging to our century) of protoplasm, or the original primordial substance, made by Max Schulze in 1863. This protoplasm, consisting of shapeless organic matter, is identical with Haeckel's celebrated monera, or those formless albumin lumps, those organless organisms out of which the true cell only develops after a long series of intermediate stages. And the moner itself, in all probability, is not the first step, but the ultimate product of previous stages of development in the process of the transformation of the inorganic into the organic. Naegeli's mechanico-physiological theory of descent goes even so far as to declare the distance between the moner and the true primordial plasma substance far greater that that between the moner and the mammal! In the light of these discoveries and the consequent conclusions, the much-ventilated question of primal generation, which formerly was covered by impenetrable darkness, no longer presents any difficulty in the way of scientific explanation.
Physiology.—In close connection with anatomy and the history of evolution, which are occupied with the physical building up of the organisms, stands physiology, or the science of the functions of the organs. Here we notice, in the first place, the great discovery made by von Baer, in 1827, of the ovum of the mammals and of man, in its original place in the ovary. This discovery was soon after followed, in 1844, by the elucidation by Th. Bischoff of the