THE CELL AND PROTOPLASM. 145 



to the activities of the cell. If the destructive 

 processes were to go on alone the organism might 

 continue to manifest its life activities for a time 

 until it had exhausted the products stored up in 

 its body for such purposes, but it would die from 

 the lack of more material for destruction. Life 

 is not complete without both processes. Now, in 

 the life of the cell we may apparently attribute 

 the destructive processes to the cell substance and 

 the constructive processes to the nucleus. In a 

 cell which has been cut into fragments those pieces 

 without a nucleus continue to show the ordinary 

 activities of life for a time, but they do not live 

 very long (Fig. 25). The fragment is unable to 

 assimilate its food sufficiently to build up more 

 material. So long as it still retains within itself a 

 sufficiency of already formed tissue for its destruc- 

 tive metabolism, it can continue to move around 

 actively and behave like a complete cell, but 

 eventually it dies from starvation. On the other 

 hand, those fragments which retain a piece of 

 the nucleus, even though they have only a small 

 portion of the cell substance, feed, assimilate, 

 and grow ; in other words, they carry on not 

 only the destructive but also the constructive 

 changes. Plainly, this means that the nucleus 

 controls the constructive processes, although it 

 does not necessarily mean that the cell substance 

 has no share in these constructive processes. 

 Without the nucleus the cell is able to perform 

 those processes, while it is able to carry on the de- 

 structive processes readily enough. The nucleus 

 controls, though it may not entirely carry on, the 

 constructive metabolism. 



