ELEMENTARY PAETS OF AN ORGAN OR TISSUE. 67 



1838, every writer on minute anatomy and physiology 

 has described at some length the structure of the "cell.'" 

 This " cell " has been regarded as the anatomical 

 unit, and it has been often stated that all the dif- 

 ferent tissues consist of "cells." The "cell" is a 

 complex body, and different properties have been 

 supposed to be manifested by the several parts of 

 which a perfect cell is composed. In order that 

 certain bodies which could not be included under the 

 ordinary definition of the cell might be comprised in 

 the cell category, the anatomical unit it was sup- 

 posed might be modified in certain special particulars 

 and ia exceptional cases. A body in. connection with 

 which no cell wall could be detected was supposed to 

 have a cell wall in a fluid state, of the consistence of 

 the soap-bubble : or it was contended that it might 

 have had a cell wall at an earlier period of its life ; or 

 the cell without wall was called a free nucleus, which 

 it was inferred had escaped from its capsule. Many 

 other ingenious devices have been adopted to evade 

 the difficulty, which has been felt by every one who 

 has examined tissues, of bringing each anatomical 

 unit at all periods of its life into the cell category. 

 But, after all, the simple fact is this, that no "cell" 

 exhibits cell wall, cell contents, and nucleus at 

 every period of its existence, while some cells do not 

 possess any structure to which either of these terms 

 can be properly applied at any period. There are, 

 then, "cells," consisting of cell wall only, and "cells " 

 consisting of a " nucleus" only, and yet the original 

 definition of cell has been repeated in ahnost all oui- 

 text-books even up to this very time. 



As regards the fonnaiion of " cells," we have the 

 most contradictory statements. Some tissues are 

 admitted not to be composed of cells at all, by autho- 

 rities who nevertheless cling to the cell theory. So 

 far from the "cell" being the essential and the 



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