SCHWANN, THEODOR (1810-1882), author of the cell theory in physiology, was born at Neuss in Rhenish Prussia on 7th December 1810. His father was a man of great mechanical talents ; at first a goldsmith, he afterwards founded an important printing establishment. Schwann inherited his father's mechanical tastes, and the leisure of his boyhood was largely spent in constructing little machines of all kinds. He studied at the Jesuits' college in Cologne and afterwards at Bonn, where he met Johannes Muller, in whose physiological experiments he soon came to assist. He next went to Wiirzburg to continue his medical studies, and thence to Berlin to graduate in 1834. Here he again met Mfiller, who had been meanwhile tmns-lated to Berlin, and who finally persuaded him to enter on a scientific career and appointed him assistant at the anatomical museum. Schwann in 1838 was called to the chair of anatomy at the Roman Catholic university of Louvain, where lie remained nine years. He then went as professor to Liege, where, in spite of brilliant offers from many German universities, he led a very quiet un-eventful life, broken only by the international commemora-tion of the fortieth anniversary both of his professoriate and the publication of his magnum opu.s, till his death on I 1 th January 1882. He was of a peculiarly gentle and amiable character and remained a devout Catholic through-out his life.

It was during the four years spent under the influence of Muller at Berlin that all Schwann's really valuable work was done. Mtiller was at this time preparing his great book on physiology, and Schwann assisted him in the experimental work reqnired. His attention being thus directed to the nervous and muscular tissues, besides making such histological discoveries as that of the envelope of the nerve-fibres which now bears his name, he initiated those researches in muscular contractility since so elaborately worked ont by Du Bois Reymond and others. He was thus the first of Mfiller's pupils who broke with the traditional vitalism and worked towards a physico-ehernical explanation of life. Midler also directed his attention to the process of digestion, which Schwann showed to depend essentially on the presence of a ferinent called by him pepsin, thus not only practically bringing the subject up to its modern state but preparing for the subsequent advances in medical treatment made by Roberts. Schwann also examined the question of spontaneous generation, which he aided greatly to disprove, and in the course of his experiments discovered the organic nature of yeast. His theory of fermentation was bitterly attacked and ridiculed by Liebig, but has been, after the lapse of a quarter of a. century, triumphantly confirmed. In fact the whole germ theory of Pasteur, as well as the antiseptic application of Lister, is thus traceable to the influence of Schwann. Once when dining with Schleiden, in 1837, the conversation turned on the nuclei of vege-table cells. Schwann remembered having seen similar stnictures in the cells of the notochord (as had been shown by Midler) and instantly seized the importance of connecting the two phenomena. The resemblance was confirmed without delay by both observers, aud the results soon appeared in the famous Microscopic Investiga-tions on the Accordance in the Structure and Growth of Plants and Animals (Berlin, 1839 ; trans. Sydenhazn Society, 1847), and the cell theory (see MonPnoLociv) was thus definitely constituted. In the course of his verifidations of the cell theory, in which lie traversed the whole field of histology, he proved the cellular origin and de-velopment of the most highly differentiated tissues, nails, feathers, enamels, &c. Although mistaken in his view of the origin of new cells, his generalization at OnCe became the foundation of all modern histolog,y, and in the hands of Virchow (whose cellular pathology is an inevitable deduction from Schwalm) has afforded the means of placing modern pathology on a truly scientific basis.

An excellent account of Schwann's life and worIc is that by Leon Fredericq (Liege, 1884).