INORGANIC FOODS. 361 



colloids will undoubtedly greatly increase our knowledge concerning the 

 work of the cell. 1 Here we are especially interested in the behavior of 

 colloids towards ions. Hardy 2 has shown that ions exert a particular 

 influence upon the condition of the colloid. Negatively charged colloids 

 are precipitated by the electropositive cations, and positively charged 

 colloids by anions. In these relations we find a new proof of how extremely 

 delicate the whole mechanism of the cell is to enable it to maintain 

 between the individual ions on the one hand, and the colloids on the 

 other in such a relation that all of its functions can take place unhindered. 

 It is perfectly clear without further explanation, that owing to the various 

 reactions taking place within the cells, at one time the action of one ion 

 is most prominent, while at another time it is that of a different one. 

 The cell must always be able to neutralize at a given moment the action 

 of any one ion. Undoubtedly physical chemistry has here pointed out 

 new paths for further investigation, and there is no question but that it 

 will enable us eventually to draw new conclusions along lines that have 

 already been studied. Here again in the operations of the delicate mechan- 

 ism of the cell, it is not right to attempt to distinguish between the physical 

 chemistry and physiological chemistry of the cells. Here and there it is 

 advisable to separate the two fields and allow them to develop individually, 

 but again and again they must come back to a common basis and 

 unite to form a broader field, which develops by different methods as 

 a whole. 



It is obvious from a study of the experiments already cited that salts 

 and water are fully as important as regards the life of the cell as its organic 

 nutriment. Just as the part played by the latter is quite a varied one, 

 so in the same way the inorganic substances participate in a number of 

 different processes. Although they do not furnish the body with energy, 

 nevertheless they do come into play during the expenditure of muscular 

 effort, whether by changes in the concentration of the solutions, or by 

 variations in the osmotic pressure, or of the surface tension, etc. 



Inorganic salts are usually present in the different foods to an extent 

 entirely sufficient for all our demands. An exception to this general rule 

 is the fact that man and certain animals require an additional supply of 

 sodium chloride. Sodium chloride is the only inorganic substance which 

 it is necessary to add to our diet. This is rather remarkable, because both 

 animal and vegetable food already contains considerable sodium and 

 chlorine. The explanation of this exceptional requirement in the case of 



1 Cf. Hans Aron: Biochem. Zentr. 3, 15, 16, 17, pp. 461 and 501 (1905). R. Zsig- 

 mondy: Zur Erkenntnis der Kolloide, Jena, 1905. H. J. Hamburger: Osmotischer 

 Druck u. lonenlehre in den medizinischen Wissenschaften, Wiesbaden, 1904. R. 

 Hober: Physikalische Chemie d. Zelle u. d. Gewebe, Leipsic, 1902. 



3 Z. physikal. Chem. 33, 385 (1900). 



