THE CEU, AND ITS LIFE. 25 



originated was not known, although the current notion was 

 that new cells arose " in between " old cells. That a tiny 

 granule, the nucleus, was in some manner deposited 

 between already formed cells, and that around this nucleus 

 the rest of the cell gradually arose by a process of precipi- 

 tation like the growth of a crystal in a supersaturated solu- 

 tion of that substance. How inconsistent that view was 

 with all the facts of heredity seemed not to be considered. 

 The remarkable advance in knowledge, that a new cell 

 arises only by a division of a pre-existing cell is due to the 

 botanist Nageli, who had observed this manner of cell pro- 

 duction. And when finally Max Schultze in our own day 

 proved the identity of protoplasm, whether taken from plant 

 or animal, the cell theory as we now understand it, was in 

 its general outlines established. Added proof was further 

 given to this theory (now really a fact) when Dujardin and 

 Haeckel showed that many of the lowest animal and plant 

 forms were in reality nothing more than single cells. 



A TYPICAL CELL. 



As the cell figures so prominently in the proper under- 

 standing of nearly all histological structures and throws so 

 much light on physiological properties and the problems 

 of heredity, a more general account of it is here given 

 as an introduction to the histological matter further on. A 

 typical cell consists of a mass of protoplasm surrounded by 

 a cell wall, and containing within it a nucleus. Food 

 material also frequently occurs diffused through the pro- 

 toplasm. Recently there was discovered a further structure, 

 lying usually close to the nucleus, the centrosome. The 

 exact nature of this body is not yet fully established, but 

 it seems to play a very important part in the division of the 

 cell. The nucleus is made up of a substance which stains 

 deeply when treated with the usual staining agents and has 

 been called chromatin. The nucleus is that part of the 

 cell which seems to influence and determine the func- 

 tion of the cell, and from the important role it plays in 



