26 THE CHEMISTRY AND PHYSICS OF THE CELL 



really did ionize. Probably all soluble substances do dissociate to a 

 certain minimal degree, but it is so slight for most of the constituents 

 of the cell except the inorganic salts (the organic acids and alkalies, 

 and a few dissociable organic products of protein metabolism, occur in 

 such insignificant amounts as to be almost negligible) that without 

 them there would be little chemical activit}^ possible, and hence life 

 would be absent or at a very low ebb indeed. As before mentioned, 

 the inorganic salts probably exist in the cell not only as salts, but also, 

 and perhaps chiefly, as ions and ionic compounds with the cell proteins. 



Many applications of the facts and theories of ionization have been 

 made in physiology and a few applications have also been made in 

 pathology, especially the relation of ions to edema, to diuresis and 

 glycosuria, and also to problems of immunity. No attempt will be 

 made here to go further into the observations and theories concerning 

 ionization or its role in physiology, but for more extensive information 

 as well as for the complete bibliographj^ the works mentioned below 

 may be referred to.^' The applications in pathology will be brought 

 out as the subject under discussion in subsequent chapters necessitates 

 and it is largely to facilitate the understanding of such reference that 

 this brief summary of the subject of ionization has been introduced. 

 In the same spirit we take up the subjects of diffusion and osmosis. 



Diffusion and Osmosis. — Although the non-electrolytes do not 

 ionize to any considerable extent, and therefore are relatively inactive 

 chemically, the crystalloidal non-electrolytes, of which sugar and urea 

 are the two chief examples among the cell constituents, possess in 

 common with the electrolytes the important property of diffusion. 

 By this process the exchange of chemical substances between the blood 

 and the cell is brought about, by it the chemical composition of the 

 different parts of the cell and between different cells is equalized, 

 and without it chemical change would be practically impossible. Dif- 

 fusion occurs most simply between two solutions of unlike nature, 

 or between a solution of a substance and the solvent alone, when 

 placed directly in contact with one another. If we place in the bot- 

 tom of a cylindrical vessel a solution of copper sulphate and above 

 it some water, carefully avoiding mixing, it will be found after some 

 time that the fluid has become equally blue throughout. This is 

 brought about by the movement of the dissolved particles which 

 gradually carries them through the entire mass of iluid, and as their 

 migration is against the force of gravity, they evidently accomplish 



" "Physical Chemistry in the Service of Medicine," Wolfgang Pauli, transla- 

 tion by M. H. Fischer, New York, 1907. " Physikalische Chemie dor Zelle und 

 der Gewehe," Hober, Leipzig, 1915. "Osmotisohe Druck und lonenlehre in den 

 medicinischen Wissenscliaften," Hamburger, Wiesbaden. "Studies in General 

 Physiology," Loci), University of Chicago Press, 1905. "Dynamics of Living 

 Matter," Locb, Columbia University Press, New York, 1906. Spiro and J. Loeb 

 Oppenheimer's "Handbuch der Biochemie," 1908 (2), 1-141. "Physical Chem- 

 istry of Vital Piienomena," McCIendon, Princeton Univ. Press, 1917. 



