24 



ANATOMY FOR NURSES 



[Chap. Ill 



virtue of its amoeboid movements, tends to flow round and en- 

 wrap the particles, and particles thus enwrapped or incepted 



may then be conveyed by 

 the cell from one place to 

 another. 



(4) Reproduction. — Like 

 all living organisms, each 

 cell grows, produces other 

 cells, and dies, so that each 

 cell has a life cycle compa- 

 rable to, but much shorter 

 than the body itself. As the 

 cells are constantly dying, 

 the need for constant repro- 

 duction is apparent. This 

 reproduction is accomplished 

 in two ways, (a) simple, di- 

 rect division or akinesis, and 

 (6) indirect division or kary- 

 okinesis, which is the almost 

 universal method. 



Fig. 7. -Diagrams illustrating division of / ) j akhiesis OT direct 

 a cell. A, resting cell with nucleus (n) and ^ ' " "^ v^l ^a 

 centrosome (c). B, preparing to divide, two division the Cell cloUgatCS, 

 asters (a) near nucleus, each with a centro- , , 1 + 1 

 some, chromatin becoming massed into chro- the nUCleUS and Cytoplasm 

 mosomes. C, two asters have formed a spindle become COUStrictcd in the 

 with chromosomes (ch) in centre. D, each chro- 

 mosome divided and two halves being moved centre, and the Ccll dividcS 

 towfird the asters. E, chromosomes forming ■, « , ii U* V. 

 the two new nuclei, and cell body beginning to ^"^ lOrmS tWO CellS wnicn 

 di\Tde. F, division complete, two-cell stage, ^qqjj gro^y tO the sizC of the 

 each cell has the same structure as the one cell . . , 

 in A. cw, cell-wall. (Bigelow from Wilson.) Original cell. 



(6) In karyokinesis or in- 

 direct division the nucleus passes through a series of remarkable 

 changes which are rather complicated. A careful study of Fig. 7 

 will give the student some idea of these changes.^ 



Differences in cells. — Cells differ in (1) size, (2) form, 

 (3) chemical composition, and (4) function. (1) They vary in 

 size from ^oVo to ^^ o^ of an inch (0.008 to 0.08 mm.) in diameter.^ 



> For a detailed description of karyokinesis the student is referred to "The Cell 

 in Development and Inheritance," by Wilson. 



' On page 469 will be found accurate ratios between the metric system and the 

 system of length, weights, and measures used in the United States. For the sake 



