THE STORY OF NINETEENTH-CENTURY SCIENCE 



The main thesis as to the similarity of development 

 of vegetable and animal tissues, and the cellular nature 

 of the ultimate constitution of both, was supported by a 

 mass of carefully gathered evidence which a multitude 

 of microscopists at once confirmed, so Schwann's work 

 became a classic almost from the moment of its publi- 

 cation. Of course various other workers at once dis^ 

 puted Schwann's claim to priority of discovery, in particu- 

 lar the English microscopist Valentin, who asserted, not 

 without some show of justice, that he was working 

 closely along the same lines. But so, for that matter, 

 were numerous others, as Henle, Turpin, Dumortier, 

 Purkinje, and Miiller, all of whom Schwann himself had 

 quoted. Moreover, there were various physiologists who 

 earlier than any of these had foreshadowed the cell the- 

 ory ; notably Kaspar Friedrich Wolff, towards the close 

 of the previous century, and Treviranus about 1807. 

 But, as we have seen in so many other departments of 

 science, it is one thing to foreshadow a discovery, it is 

 quite another to give it full expression and make it 

 germinal of other discoveries. And when Schwann put 

 forward the explicit claim that " there is one universal 

 principle of development for the elementary parts of 

 organisms, however different, and this principle is the 

 formation of cells," he enunciated a doctrine which was 

 for all practical purposes absolutely new, and opened 

 up a novel field for the microscopist to enter. A most 

 important era in physiology dates from the publication 

 of his book in 1839. 



IV 



That Schwann should have gone to embryonic tissues 

 for the establishment of his ideas was no doubt due very 



