CHAPTER II. 

 NUCLEI AND KINETIC ELEMENTS. 



In the preceding chapter plastids in protoplasm were interpreted 

 as substances of more or less homogeneous nature which act as 

 centers of specific activities or activity. Kinetic elements of the 

 cell might well be included in this category of plastids since they 

 are apparently composed of homogeneous substance and have 

 specific activities in connection with the \isible expressions of the 

 transformation of energy through destructive metabolism. Nuclei, 

 on the other hand, are not homogeneous substances, but are aggre- 

 gates of substances of different kinds and amongst these substances 

 are some which are unmistakably kinetic in function. These 

 aggregates of substances are the centers of a great variety of activi- 

 ties in the cell, the importance of which is evident by the simple 

 experiment of cutting a cell so that one fragment contains the 

 nucleus, while the other fragment has none. The enucleated frag- 

 ment is unable to digest and assimilate food or to grow; nor is it 

 able to reproduce, nor to regenerate lost parts except under certain 

 circumstances (see p. 485) . Nucleated fragments on the other hand 

 are able to do all of these and continue to live as normal organisms. 



Chomatin and kinetic elements are closely associated in protozoan 

 nuclei and no adequate discussion of either is possible without a 

 discussion of both. Here the nucleus is not only the site of chro- 

 matin aggregates but there is abundant evidence, and further evi- 

 dence is constantly accruing, to support the view that the nucleus 

 is the original seat of kinetic elements as well. The well-known 

 views of Schaudinn (1904), the oft-repeated statements of Hartmann 

 and of Kofoid, and the conclusions of Jollos (1917), of Belar (1920) 

 and others, all agree in regarding the nucleus of a protozoon as a 

 combination of kinetic and idiogenerative elements. 



I. THE NUCLEI OF PROTOZOA. 



The term "nucleus" is ordinarily applied in a morphological rather 

 than a physiological sense. If the activities of the component parts 

 of the nucleus are absolutely necessary for the maintenance of life 

 of the cell, then, in some cases such as IloJosticha, Trochelucerca, 

 or Bilephis anser, such activities must be performed by substances 

 which appear to be identical with chromatin but which are dis- 

 tributed throughout the cell. On the other hand, it is highly prob- 



