THE BEGINNINGS OF LIFE. 149 



middle of it.' He also is disposed to attach much 

 importance to the nucleus, and believes that c as long 

 as cells behave as elements still endowed with vital 

 power, the nucleus maintains a very constant form/ 

 Thus, according to Virchow, c every animal presents 

 itself as a sum of vital unities j or as a large kingdom 

 made up of an enormous aggregate of minute depend- 

 encies, each of which is endowed with more or less 

 power of self-government these dependencies being 

 invariably constituted by definite morphological units 

 known as cells, though there may or may not be in- 

 cluded under the sway of each a certain outlying 

 c cell territory.' Such is the essence of Virchow's 

 doctrine. 



Before proceeding further, however, it will be well 

 to point out that important modifications had been 

 growing up, even before the publication of Virchow's 

 theories, as to the true conception of the nature of a 

 cell. So far the cell has been spoken of as an alto- 

 gether definite structure as a body with a distinct wall 

 or bounding membrane and also certain contents, which 

 include amongst other things one of the most funda- 

 mental parts of the cell, the nucleus which again 

 may contain a nucleolus. But it was maintained by 

 Naegeli *, and also by Alexander Braun 2 , and then more 



1 'Zeitschrift fur Wissen. Botanik,' 1846 (Transln. Ray Soc. 1849, 



P- 95)- 



2 'The Phenomena of Rejuvenescence in Nature,' 1851 (Transln. 



Ray Soc. 1853). 



