48 THE EIDDLE OF THE UNIVEESE. 



discovery. He himself sought to point out the same 

 composition in various tissues of the animal body 

 — for instance, in the spinal chord of vertebrates — 

 and thus led his pupil, Schwann, to extend the dis- 

 covery to all the animal tissues. This difficult task was 

 accomplished by Schwann in his Microscopic Researches 

 into the Accordance in the Structure and Growth oj 

 Plants and Animals (1889). Thus was the foundation 

 laid of the " cellular theory," the profound importance 

 of which, both in physiology and anatomy, has become 

 clearer and more widely recognised in each subsequent 

 year. Moreover, it was shown by two other pupils of 

 Johannes Miiller — the able physiologist, Ernst Briicke, 

 of Vienna, and the distinguished histologist, Albert 

 Kolliker, of Wurzburg — that the activity of all 

 organisms is, in the ultimate analysis, the activity of 

 the components of their tissues, the microscopic cells. 

 Briicke correctly denominated the cells the " elemen- 

 tary organisms," and showed that, in the body of 

 man and of all other animals, they are the only actual, 

 independent factors of the life-process. Kolliker 

 earned special distinction, not only in the construction 

 of the whole science of histology, but particularly by 

 showing that the animal ovum and its products are 

 simple cells. 



Still, however widely the immense importance of 

 the cellular theory for all biological research was 

 acknowledged, the " cellular physiology " which is 

 based on it only began an independent development 

 very recently. In this Max Yerworn (of Jena) earned 

 a twofold distinction. In his Psycho-physiological 

 Studies of the Protistce (1889) he showed, as a result 

 of an ingenious series of experimental researches, that 

 the "theory of a cell-soul" which I put forward in 



