32 



COLLOIDS IN BIOLOGY AND MEDICINE 



food materials, which are taken up at the places where needed, stored, 

 and when necessary given up again. In other words, the organ- 

 ism, plant as well as animal, is a vessel containing an aqueous solu- 

 tion in which various colloids exist as dispersed phases. The balance 

 which rules at each moment is disturbed by food material entering 

 the vessel and by the metabolic products developing in it, and 

 these become distributed between the solvent and the dispersed 

 phase, the organ-colloids. In this entire chapter we have treated 

 the simple case occurring when a single dispersed phase exists in a 

 single dispersing medium (solvent). We may still assume without 

 serious error, that there is one dispersing medium; but instead of 

 one dispersed phase in the organism we have dozens, perhaps hun- 

 dreds, of dispersed phases. Each individual class of cells is a dif- 

 ferent dispersed phase with different properties. Only in this way 

 can we understand how the assimilation products are sorted, stored 

 up and changed into the tissues of the several organs. 



To quote a single example, we find (according to a table in E. 

 ABDERHALDEN'S Textbook of Physiological Chemistry) that there are 

 the following distributions: 



It is difficult to imagine a more unequal distribution. For in- 

 stance, potassium and sodium salts enter the circulation as electro- 

 lytes to the same extent; and there can be no question of any 

 irreversible chemical combination of these salts either with the serum 

 or with the blood corpuscles, since both diffuse away when the serum 

 or blood corpuscles are brought in contact with pure water. There 

 is thus a condition of equilibrium in the blood by which the blood 

 corpuscles dissolve or adsorb proportionately more potassium salts, 

 while the serum albumin dissolves or adsorbs more sodium salts. This 

 is not a unique case, for humus adsorbs chiefly the potassium salts 

 from a mixture and permits the sodium salts to pass through. With 

 iron the conditions are different; it certainly must enter the organism 



