20. 



THE HUMAN BODY 



with the highest powers of the microscope. The main bulk of the 

 cell, surrounding the nucleus, is the cell-body, and in some cases 



is inclosed in an envelope or sac, which, 

 however, when present, plays but a 

 secondary or passive part in cell divi- 

 sion. The cell-body, known also as the 



c- K^rtJv^lOttiigflCMEa cell-protoplasm (Fig. 7), consists of a net- 

 work of extremely fine threads, the re- 

 ticulum or spongioplasm, the meshes of 

 which are occupied by a different sub- 

 FIG. 7. Diagram of an ani- stance, the hyaloplasm: the proportions 



mal cell, a, hyaloplasm; 6. , , , , 



reticuium; c, nucleus, a and of hyaloplasm, and spongioplasm vary in 

 b together form the cell-body. different cells and often in different parts 



of the same cell; in fact a layer of hyaloplasm unmixed with 

 spongioplasm frequently exists on the exterior of the cell, and the 

 hyaloplasm appears to be the more immediately concerned in the 

 activities of the living cell. In addition there is to be found, im- 

 bedded in the cell-body and near the nucleus or attached to it, an 

 extremely minute particle, the attraction-particle or centrosome, 

 near which a radial arrangement of the cell-substance may often 

 be observed. 



The nucleus (Fig. 8) of a resting cell, that is of a cell not in proc- 

 ess of division, consists of an amor- 

 phous material (nucleoplasm) which 

 is perhaps similar in composition to the 

 hyaloplasm, and a filamentous ma- 

 terial, different from spongioplasm, 

 and named chromoplasm or karyo- 

 plasm. As proved by its behavior 

 with staining fluids and other reagents 

 karyoplasm is quite different chemic- 

 ally from the spongioplasm of the 



FIG. 8. Diagram of a resting 



Cell-body. One or more granules (nu- nucleus, a, nuclear membrane; 



-, 7 . x , . , i_ r i vi &> nucleoplasm; c, nucleolus; d, 



Cleoll) Which may be found Within chromoplasm ; e, some of the sur- 



most nuclei are probably local accu- 



mulations of chromoplasm; a mem- dicated. 



brane (nuclear membrane) which surrounds the nucleus of cells 



not in process of division is also probably composed of chromo- 



plasm. 



