INTRODUCTION 



10 



Oken claimed to have witnessed "repeated vesicles" in animals and 

 plants, in 1808, but it is not clear what he meant nor whether he actually 

 saw them. 



None of the writers mentioned appeared to regard these objects as 

 units of structure, nor to attach any importance to them. However in 

 the hands of Schwann (Fig. 9) and Schleiden (Fig. 10), chiefly the 

 former, repeated observation of these minute units of structure led to a 

 great generahzation. The units had been called "cells" since the time 

 of Hooke, from a mistaken notion of their structure, and Schwann and 

 Schleiden reached the conclusion that all animals and plants are built 

 up of them. This generalization was called the Cell Theory. The cor- 



Fig. 9.— Theodor Schwann, 181Q-1882. 

 (From Garrison's History of Medicine.) 



Fig. 10 — Matthias Joseph Schleiden, 

 1804-1881. (From Garrison's History of 

 Medicine.) 



rectness of their conception has since been abundantly verified, so that 

 it should now rather be spoken of as the Cell Doctrine. Although 

 Schleiden published his observations a little earlier than Schwann (1838 

 and 1839, respectively), it is only in the work of Schwann that the cell 

 theory is stated, or that the words "cell theory" are used. So that, 

 although Schleiden is usually named before Schwann in attributing to 

 them the joint authorship of this theory, it is done so rather for the sake 

 of euphony than from any desire to give Schleiden greater credit than, 

 or even equal credit with, Schwann. 



The importance of the cell doctrine can scarcely be over-estimated. 

 It is taken as a matter of course, by beginning students, that all organisms 



