THE ANIMAL CELL 2*J 



Experiments also show that the division of the cytoplasm may 

 be checked or interrupted by external influences without 

 interfering with the division of the nucleus. On the other hand 

 nuclei separated from cytoplasm are incapable of continuing 

 their functions. We are at least safe in saying that these three 

 bodies, the centrosome, the nucleus, and the cytoplasm act as 

 intracellular stimuli upon each other, and that all are important 

 in the work of the cell. During nuclear division there is prob- 

 ably increased interchange between the cytoplasm and nucleo- 

 plasm. The breaking down of the nuclear membrane facili- 

 tates this. 



43. Exercises for Library and Laboratory. The teacher should by all means 

 secure preparations of properly stained cells showing the principal structures; also 

 some of the stages of cell division (see Appendix: Laboratory Suggestions). 



What are chromosomes? In what respects and to what extent do nuclei differ? 

 What is meant by the "cell-doctrine " ? Give an outline of its history. What are 

 mitochondria? Compare the various series of figures in your library illustrating 

 the stages of cell division. 



44. Summary. 



1. The cell may be considered as the unit of structure, and 

 is to be defined as a "nucleated mass of protoplasm with or 

 without a cell membrane." 



2. The cell may also be considered the unit of function, in 

 the sense that it embodies all vital functions in epitome. 



3. The structure of the typical cell may be outlined as 

 follows : 



(a) Cell body 



Cytoplasm living. 

 Cytolymph non-living, fluid. 

 Metaplasm non-living, solid. 



(6) Nucleus: 



Nucleoplasm living. 

 Chromatin. 

 Achromatin. 



Nucleolymph non-living, fluid. 

 Metaplasm non-living, solid. 

 [Protoplasm = Cytoplasm + nucleoplasm.] 



