THE CELL 5 



as being a definite chemical substance, as its composition 

 changes. It is a viscid, colorless, semifluid material 

 having a higher index of refraction than water, and hence 

 appears brighter. It was called slime by Schleiden. 

 The protoplasm of the cell has a definite structural 

 arrangement appearing as a meshwork, or reticulum, and 

 a ground substance, or cell-sap, filling the intervening 

 spaces. In addition to these two definite substances 

 there are present in the protoplasm minute granules 

 or microsomes which are distributed regularly or irregu- 

 larly along the lines of the meshwork. While other 

 materials are often found in the protoplasm, the above 

 materials are regarded as the essential elements of pri- 

 mary importance in the activities of the cell. 



7. The nucleus. The nucleus is the center of the 

 constructive activities of the cell. When the nucleus is 

 destroyed, those processes which result in the growth 

 and development of the organism can no longer take 

 place. Only destructive activities are possible in a cell 

 devoid of a nucleus, and these can go forward for only a 

 limited time. " The nucleus is generally regarded," says 

 Wilson, " as a controlling center of cell activity, and hence 

 a primary factor in growth, development and the trans- 

 mission of specific qualities from cell to cell, and from 

 one generation to another." l Growth is the result 

 of cell division, and the impetus for cell division appears 

 to come from the nucleus. The essential fact in cell 

 division is that a portion of the nuclear material of the 

 parent cell shall pass into the new cell. The new cell 

 in its turn becomes a parent cell, and so the process of 

 growth continues. The nucleus is typically spherical 

 and moves freely within the cell. It exhibits two distinct 



1 Wilson, "The Cell in Development and Inheritance," p. 30. 



