II. Method. 



Of the different methods which have been employed to 

 solve the problem of the function of the cell nucleus, the 

 one which has given the most illuminating results is the 

 method of extirpation: removing the nucleus and comparing 

 the enucleated cell with a normal nucleated cell. In order 

 that the nucleus may be removed from a cell, or that a cell 

 may be cut in half, it is necessary or expedient that a 

 cell of considerable size be selected; but at the same 

 time it must be a cell which can be kept alive or cultivat- 

 ed for several generations if necessary. The cells which 

 meet these requirements most exactly are certain unicell- 

 ular organisms, certain protozoa. Among such a large and 

 diverse group of organisms, it is not difficult to find 

 one which is peculiarly suited for the oroblem at hand. 

 For the experiments which follow, Ameba proteus vas select- 

 ed. Owing to the slow movements and absence of shell in 

 this organism, it can readily be cut in half: or if desir- 

 ed the nucleus nay, after some practice, be removed with 

 as little as one tenth or less of the protoplasm. Moreover, 

 the lack of differentiation in Ameba is a decided advantage, 

 for we are cei-tain that in removing oart of the protoplasm 



(21) 



