THE CELL DOCTRINE. 151 



of cells, — cell division, free cell formation, and re- 

 newal (vollzellbildung) of cells. He says that in the 

 animal kingdom cell division seems to be the only 

 authenticated mode of increase of cells. Of methods 

 of free cell formation, only a few instances are re- 

 corded in vegetables. The last method, renewal or 

 rejuvenescence, has reference rather to the complete 

 formation or development of cells than to their 

 origin. 



Nutrition of Cells. — In the nutrition of the cell, the 

 pabulum comes to it from the periphery, being 

 strained through the formed material. The new 

 germinal matter takes its place in or near the centre 

 of the original mass, constituting, according to Beale, 

 a new centre of germinal matter, which may be the 

 nucleus, if no other circumscribed centre be present, 

 or the nucleolus, if it be deposited within such a centre. 

 Other new centres, according to him, may again take 

 position within these, and assume the relation of nu- 

 cleolus to the original nucleolus, which now becomes 

 the nucleus, an older centre of germinal matter ; 

 while the original nucleus has probably been con- 

 verted into the second constituent of the cell, the 

 formed material. If the nucleolus be what Klein con- 

 siders it, a mere thickening of the intranuclear net- 

 work referred to, this order of succession in the for- 

 mation of differentiated centres of germinal matter 

 is of course impossible, and it can only be said that 

 the new matter takes its position towards the centre 

 of the cell mass. 



Amceboid Movement (Diapedesis). — Germinal mat- 

 ter, when free and living, exhibits a power of move- 



