Schleiden was educated as a lawyer, and began the practice of that profession, but his taste for natural science was so pronounced that when he was twenty-seven years old he deserted law, and went back to the university to study medicine. After graduating in medicine, he devoted himself mainly to botany. He saw clearly that the greatest thing needed for the advancement of scientific botany was a study of plant organization from the standpoint of development. Accordingly he entered upon this work, and, in 1837, arrived at a new view regarding the origin of plant cells. It must be confessed that this new view was founded on erroneous observations and conclusions, but it was revolutionary, and served to provoke discussion and to awaken observation. This was a characteristic feature of Schleiden's influence upon botany. His work acted as a ferment in bringing about new activity.
The discovery of the nucleus in plant cells by Robert Brown in 1831 was an important preliminary step to the work of Schleiden, since the latter seized upon the nucleus as the starting-point of new cells. He changed the name of the nucleus to cytoblast, and supposed that the new cell started as a small clear bubble on one side of the nucleus, and by continued expansion grew into the cell, the nucleus, or cytoblast, becoming encased in the cell-wall. All this was shown by Nägeli and other botanists to be wrong; yet, curiously enough, it was through the help of these false observations that Schwann arrived at his general conclusions.
Schleiden was acquainted with Schwann, and in October, 1838, while the two were dining together, he told Schwann about his observations and theories. He mentioned in particular the nucleus and its relationship to the other parts of the cell. Schwann was immediately struck with the similarity between the observations of Schleiden and certain of his own upon animal tissues. Together they went to his laboratory and examined the sections of the dorsal cord, the particular structure upon which Schwann had been working. Schleiden at once recognized the nuclei in this structure as being similar to those which he had observed in plants, and thus aided Schwann to come to the conclusion that the elements in animal tissues were practically identical with those in plant tissues.
Schwann.—The personalities of the co-founders of the cell-theory are interesting. Schwann was a man of gentle, pacific disposition, who avoided all controversies aroused by his many scientific discoveries. In his portrait (Fig. 74) we see a man whose striking qualities are good-will and benignity. His friend Henle gives this description of him: "He was a man of stature below the medium, with a beardless face, an almost infantile and always smiling expression, smooth, dark-brown hair, wearing a fur-trimmed dressing-gown, living in a poorly lighted room on the second floor of a restaurant which was not even of the second class. He would pass whole days there without going out, with a few rare books around him, and numerous glass vessels, retorts, vials, and tubes, simple apparatus which he made himself. Or I go in imagination to the dark and fusty halls of the Anatomical Institute where we used to work till nightfall by the side of our excellent chief, Johann Müller. We took our dinner in the evening, after the English fashion, so that we might enjoy more of the advantages of daylight."
Schwann drew part of his stimulus from his great master, Johannes Müller. He was associated with him as a student, first in the University of Würzburg, where Müller, with rare discernment for recognizing genius, selected Schwann for especial favors and for close personal friendship. The influence of his long association with Müller, the greatest of all trainers of anatomists and physiologists of the nineteenth century, must have been very uplifting. A few years later, Schwann found himself at the University of Berlin, where Müller had been called, and he became an assistant in the master's laboratory. There he gained the powerful stimulus of constant association with a great personality.
Fig. 74.—Theodor Schwann, 1810-1882.
In 1839, just after the publication of his work on the cell-theory, Schwann was called to a professorship in the University of Louvain, and after remaining there nine years, was transferred to the University of Liège. He was highly respected in the university, and led a useful life, although after going to Belgium he published only one work—that on the uses of the bile. He was recognized as an adept experimenter and demonstrator, and "clearness, order, and method" are designated as the characteristic qualities of his teaching.