26 Tin: CHEMISTRY AM> I'lIYHICH OF THE CELL 



Since glj^eogen is formed from dextrose and is constantly breaking 

 down into dextrose, it is probable that the latter is also constantly 

 present in the cells. 



INORGANIC SUBSTANCES 



Up to this point the substances of the cytoplasm that have been dis- 

 cussed have all been organic compounds which do not naturally exist 

 independent from living or once living cells, yet the inorganic sub- 

 stances of the protoplasm are also of vital importance. As Mann 

 says, "so-called pure ash-free proteins are chemically inert, and, in 

 the true sense of the word, dead bodies. AVhat puts life into them 

 is the presence of electrolytes." The various salts of i)otassium, so- 

 dium, calcium, magnesium, and iron which all cells contain do not exist 

 merely dissolved in the water of the cell, but in part they are com- 

 bined with tlie organic constituents of the protoplasm. They are not 

 combined as simple additions of the salts to the proteins ; but ions, both 

 anions and cations, are united in chemical combination to the large pro- 

 tein molecule (ion-proteins). Possibly the proteins participate in vi- 

 tal chemical processes only as ion compounds with inorganic elements. 

 It is extremely difficult, indeed almost impossible, to secure proteins 

 entirelj^ free from inorganic substances (ash-free proteins). The fact 

 that inorganic substances are held in the cells chemically rather than 

 by simple diffusion into them from the surrounding fluids is sho^^m 

 by the great difference in the proportions of various salts in the cells 

 and in the extra-cellular fluids. Thus potassium is nearly always 

 much more abundant in the cells than in the tissue fluids, while so- 

 dium is more abundant in the fluids. Phosphoric acid is also more 

 abundant in the cells, and chlorin in the plasma. In cells iron seems 

 to exist chiefly in combination with the nucleo-proteins. These mat- 

 ters will be taken up in greater detail in considering the physical 

 chemistry of the cell." 



THE PHYSICAL CHEMISTRY OF THE CELL AND ITS CONSTIT- 

 UENTS "^ 



From the standpoint of physical chemistry the cell consists of 

 a collection of colloids and crystalloids, electrolytes and non-electro- 

 lytes, dissolved in water, in lipoids, and in each other, surrounded by 

 a semipermeable membrane, and perhaps subdivided by similar mem- 

 branes or surfaces. Physical chemical processes, as we shall see later, 

 play an all-important part in the life phenomena of the cell, and 

 therefore some s])ace may l)e occupied ])rofitably in explaining tlie 

 nature of these changes and of the substances that particii)ate in them. 



14 Soe ^raf'.alluni on ^tici'oclioinistry, l^rfxobnissc Pliysiol., lOOS (7), 5;">2. 

 i-t'i S(>e I'.ayliss, ■"I'liiiciph's of (icMicral Pliysiok)gy,"' London, 1015, for a more 

 extensive diseiissinii of lliese (opii-s. 



