24 



THE HUMAN BODY 



indicate most convincingly that the chromatin is vitally concerned 

 in the determination of the nature of the cell. 



Outside the nucleus, and imbedded in the cytoplasm is a struc- 

 ture, the attraction sphere, which takes active part in the process of 

 cell division (Fig. 6). 



Mitotic Cell Division. Since the chromatin is looked upon as 

 determining the character of the cell, we will expect to find that in 

 the process of cell division, whereby tissues are built up out of a 



Attraction -sphere enclosing two centrosomes. 



Nucleus 



Plasmosome or 



true 



nucleolus 



Chromatin- 



network 



Linin-network 



Karyosome, 

 net-knot, or 

 chromatin- 

 nucleolus 



Plastids lying 

 in the cyto- 

 plasm 



Vacuole 



'assive bodies 

 (metaplasm or 

 paraplasm) 

 suspended in 

 the cyto- 

 plasmic mesh- 

 work 



FIG. 6. Minute structure of a cell (Wilson). 



few antecedent cells, care will be taken to divide the chromatin 

 of the dividing, or mother cell equally between the daughter cells, 

 so as to insure that the lattef shall be alike. Similarly, in the 

 earlier stages of development, when the different tissues of the 

 body are being formed from cells that are all alike, means must be 

 afforded for dividing the chromatin of the mother cell unequally 

 among the daughter cells, to make the desired differentiation pos- 

 sible. The processes by which these ends are secured are known as 

 mitosis or mitotic cell division. 



The first step in mitotic division is the splitting of the attraction 

 sphere (Fig. 6) into two halves, called the centrosomes, which travel 



