124 THE EVOLUTION OF MAN. 



organized cell-state. The human body is not in reality a 

 simple life-unit, as is at fii'st the universally current, simple 

 belief of men. It is, rather, an extremely complex social 

 community of innumerable microscopic organisms, a colony 

 or a state, consisting of countless independent life-units, of 

 different kinds of cells.*^ 



The term cell is, in reality, not well chosen. Schleiden, 

 who first introduced it as a scientific term in the sense in 

 which it is used in the cell theory, named the little element- 

 ary organisms "cells," because in a cross-section of most 

 parts of plants, they look like chambers, which, like the cells 

 of a honeycomb, are massed together, are separated by solid 

 walls, and are filled with liquid or a soft pulpy substance. 

 This conception of the cell, as held by Schwann, namely, 

 that it was a small closed sac, or bladder, filled with a 

 fluid, and surrounded by a solid envelope, or wall, continued 

 prevalent for a long time ; but in the case of most of the 

 cells in the animal body, it is altogether inapplicable. The 

 further the investigation of the cells of the animal body was 

 carried, the more evident it became that the cell must be 



4 



Fig. 2. — Ten cells from the liver ; one (b) has two kernels. | 



Fig. 3. — Three epithelial cells from the mucous membrane of the tongue. ^ 



