CELLS AND THE CELL THEORY 45 



5. Reproduction. Reproduction is the direct result of assimi- 

 lation; for assimilation produces growth, and growth in the end 

 results in division. All forms of reproduction take the form of 

 division. 



The four properties, irritability, conductility, assimilation, and 

 reproduction, have been described as belonging to protoplasm; 

 and the mechanical theory of life has centered around this con- 

 ception. But in a sense it is misleading to call them properties 

 of protoplasm, unless in the term protoplasm we include all of 

 the contents of a cell, the nucleus as well as the cell substance. 

 A living cell shows these general properties; but the living 

 cell consists of protoplasm and nucleus, both of which are neces- 

 sary in order that all the functions mentioned should be shown. 

 The material frequently called protoplasm, i. e., the substance 

 outside of the nucleus, does not show all these functions. We 

 ask, therefore : What are the functions of the nucleus and proto- 

 plasm as distinct from each other? To draw a sharp line 

 between them is not possible at present. 



3. THE NUCLEUS AND ITS SIGNIFICANCE (1880 TO THE 

 PRESENT) 



In the early study of the cell the nucleus was looked upon as 

 an unimportant part, and in all of the early discussions its sig- 

 nificance was generally neglected. From about 1880 the modern 

 microscope and modern methods began to be directed towards 

 the nucleus, and a series of marvelous and unexpected results 

 were obtained, leading to the recognition of the nucleus as perhaps 

 the most important part of the cell, and as possessing a structure 

 of wonderful complexity and marvelous properties. The struc- 

 ture of the nucleus has already been outlined and may be seen in 

 Figure 12. These figures are enough to disprove any idea that 

 either cytoplasm or nucleoplasm can be considered a definite 

 chemical substance. They indicate clearly that in the simplest 

 life unit, we are not dealing with a homogeneous compound but 

 with a complex structure and a mechanism of delicate adjust- 



