82 THE CELL DOCTRINE. 



embryo of the freshwater snail, while Valentin had 

 furnished examples of the development of fibres 

 out of cells in the muscular fibres, and in the sub- 

 stance of the crystalline lens. In fact, as stated by 

 Dr. Waldo J. Burnett, in his admirable paper,* Val- 

 entin " perceived the true physiological relations of 

 cells as far as he well could without apprehending 

 the grand fact that the nucleated cell is the funda- 

 mental expression of organic forriis." 



Virchow had also compared the whole organism 

 to a free state containing individuals endowed with 

 equal privileges if not with equal powers.f 



SCHLEIDEN AND SCHWANN, 1838. 



It was reserved for Schwann to accomplish this mas- 

 terstroke in observation and generalization, through 

 the intermediate results of Schleiden, without whose 

 observations on vegetable structures, the true position 

 of the cell would probably have remained undetected 

 foi» some time longer. Schleiden, in 1838, clearly 

 pointed out the formation of cells in vegetable struc- 

 tures, according to a single and uniform method, and 

 elaborated the theory of development of which the 

 cell was the unit, and which Schwann immediately 

 extended to animal tissues. 



* Burnett, W. J., The Cell; its Physiolosy, Pathology, and 

 Philosophy, as deduced from original investigations. To which is 

 added its History and Criticism. A prize essay, read before the 

 American Medical Association, and published in vol. vi of its 

 Transactions. Philadelphia, 1853. 



f Strieker, op. citat., p. 2. 



