THE CELL DOCTRINE. 41 



Thus is formed the animal cell according to 

 Schwann, and although its method is very similar to 

 that of Schleiden, hoth as to endogenous and exoge- 

 nous cell formation (for Schwann did not restrict 

 cell genesis to endogenous cell formation), we have' 

 quoted his own paper because he is plainly fuller and 

 more precise in his descriptions. The object of each 

 observer was, however, the same with regard to the 

 Uissues studied; the additional object of Schwann 

 being to show that all organisms,'v{'h&ih%r animal or 

 vegetable, are formed on a common principle, and that 

 this principle is origin from cells, — that the various 

 tissues of the plant and animal, however simple or 

 complicated, are all combinations of these cells, modi- 

 fied in adaptation to the special peculiarities of tis- 

 sues. 



The conception of Schleiden was truly original, 

 though its application was less difficult in conse- 

 quence of the simplicity of vegetable tissues. The 

 conception of Schwann was easier, in being the re- 

 flection of that of Schleiden, while its application 

 was more difficult, in consequence of the great diver- 

 sity of animal tissues ; so difficult that he acknowl- 

 edged that " there are some exceptions, or at least 

 differences, which are as'yet unexplained." This need 

 not surprise us when we recollect that one of the ablest 

 modern exponents of the cell theory admits the diffi- 

 culty of its application to some of the so-called higher 

 tissues.* Indeed, the careful reader of Schwann's 



* Virchow, Cellular Pathologj, Chance's Translation. Am. 

 Edit., Philadelphia, 1863, p. 78. 



4* 



