SKETCH OF THE ODOR SCHWANN. 261 



Liebig's contradictions or to his joke. He bided bis time. It 

 came in a quarter of a century, when Schwann saw his theory- 

 extended to cover a great variety of chemical and pathological 

 actions, and almost universally accepted ; and received in 1878, 

 from Pasteur, who had carried it to its highest triumph, a letter 

 recognizing him as the one who had opened the road by follow- 

 ing which his own wonderful discoveries were made. 



These researches might of themselves have sufficed to make 

 the name of Schwann illustrious. But they are relatively but 

 little known because their fame has been dimmed in the face of 

 the incomparable luster of his great discovery of the cell theory. 

 The publication of the book in which the basis of this theory was 

 laid down opened a new era in biological study. We might search 

 in vain, says Simon, in his History of the Natural Sciences, for an 

 example of a more radical revolution in the direction and character 

 of scientific labors than that which was effected in 1838 and 1839 

 by the publication of Schwann's histogenetic theory. The revolu- 

 tion was sudden, and triumphed, we might say, without resistance. 

 As Henle has remarked, the scientific soil in which this theory 

 took root and grew had been prepared from two different points 

 of view : one, philosophical or ideal ; the other, positive or histo- 

 logical. The philosophical preparation dated from the beginning 

 of the study of Nature, and was illustrated in the propensity of 

 the human mind to look for some simple cause for the diversity of 

 phenomena. To this we owe the monads of Epicurus and Leib- 

 nitz, Oken's philosophy of Nature, and many other efforts ancient 

 and modern. On the other side, certain histological researches, 

 often very modest, but coming close to the facts, had prepared a 

 way for the cell theory. Robert Brown had discovered the cellu- 

 lar nucleus in 1831 ; Mirbel, Von Mohl, and Unger had demon- 

 strated that the organs and tissues of plants were at bottom 

 aggregations of cells in different degrees of transformation. 

 Schleiden had been studying the important part played by the 

 nucleus in the formation of vegetable cells, and had given it the 

 name of cytoblast ; and other authors had found in animals or- 

 gans formed of cells. But these were as yet only isolated facts. 



Schwann has himself told the story of the way the idea of his 

 discovery first occurred to him. " One day," he says, " when I 

 was dining with M. Schleiden, that illustrious botanist spoke of 

 the important part which the nucleus plays in the development 

 of plant-cells. I at once recollected that I had seen a similar 

 organ in the cells of the dorsal cord, and instantly appreciated 

 the extreme importance the discovery would have if I could show 

 that it plays the same part there as the nucleus of plants in the 

 development of vegetable cells. It must follow, in fact, in conse- 

 quence of the identity of so characteristic phenomena, that the 



