48 THE CHEMISTRY AND PHYSICS OF THE CELL 



as if it were Ixtuiid into a fixed strueture by a framework. Other 

 cells, however, retain their form under tlie same conditions. The 

 structure of even so evidently complicated a cytoplasm as that of 

 striated muscle fibers is in doubt ; a classical observation on this point 

 is the passage of a minute worm through the substance of a muscle- 

 cell, its progress being as unimpeded as if there were no such things 

 as disks, bands, rods, and stria^ in the cell. INIany features of 

 ameboid movement also seem to indicate that the cytoplasm follows 

 much the same laws as a drop of fluid in a heterogeneous medium, for 

 we can make a drop of mercury or of chloroform in water, or of oil 

 in weak alcohol, react to various stimuli in much the same way that 

 an ameba would. If we look upon the cytoplasm as a drop of emulsion 

 colloid, the surfaces of the particles in the emulsion furnish of them- 

 selves adequate explanation of many of the phenomena of isolation 

 of chemical reactions, etc., without lacking in harmony with the evi- 

 dences of structural homogeneity. This hypothesis fits all sides of 

 the problem and has many supporters at the present time.^* 



The question of structure in the nucleus is quite a different matter, 

 in so far as the chromatin threads and the nucleolus are concerned. In 

 ameboid movement the nucleus seems to play a passive role and to 

 be dragged about by the cytoplasm, indicating quite a high degree of 

 rigidity. It is probable, however, that the achromatic portion between 

 the chromatin threads and granules has much the same structure or 

 lack of structure as the cytoplasm. 



The inorganic salts seem to be, at least in part, contained in the 

 cells in chemical combination rather than in simple solution in the 

 water of the cell. There is much evidence indicating that they form 

 with the proteins ion compounds, which may be altered under various 

 conditions. For example, Loeb found that muscles placed in solutions 

 of potassium salts took up much water, whereas if placed in a solution 

 of calcium salts they lost water, exactly as soaps do w^hen potassium or 

 calcium ions are substituted for the sodium ions in a sodium soap. 

 He has suggest(Ml that we have in the cells a protein-ion compound, 

 after this order, Xa 



/ 



Protein — K 



\ 



Ca 



aiid that if, in the surrounding fluid, a great excess of one of these 

 ions is present, it may displace the others by mass action, forming a 

 protein with all or most of the ions of one kind, and, therefore, de- 

 cidedly abiioi-mal. ^Fany features of cell physiology seem explainable 

 on these o-rouiids, and the reader is referred to Loeb's collected wcu-ks 

 for fnrtlici- discnssion ; ^^ also to Clowes' interesting investigations 



34 An oxcollont discussion of tliis (|iu'slinn is j^iven liv Alsljorji:, Scioiico. lOll 

 (34), 07. 

 30 "Studios in Coneral Pli\>ioi()>'V," ]!)05. 



