158 PHYSIOLOGY OF MICROORGANISMS 



From the diagram it will also be noted that, whether in true solution or 

 colloidal solution, solutions are not confined to the action of water on 

 some salt but extend in like manner to gaseous, liquid and solid alike, 

 as gas in gas, solid in gas, gas in solid, liquid in gas, liquid in solid, etc. 



The solute may exist in the form of a substance which becomes 

 electrically dissociated into its ions, as sodium chloride is dissociated 

 into its ions, sodium and chlorine, in water, when it is called an elec- 

 trolyte. The solute may be resolved only into its molecules in water, as 

 sugar, when it is called a non-electrolyte. Such substances are desig- 

 nated usually as crystalloids, but this is not uniformly so. Again, 

 instead of using the term solute, in its place there is used the term 

 disperse phase. This is made of small particles greater in size, as a rule, 

 than molecules, and only in suspension. The solution takes on the 

 differentiated form as represented by heterogeneous, polyphasic, and 

 colloidal characters. The so-called solid solution signifies that one 

 solid substance may become distributed throughout another solid 

 substance as in the case of "crystals which are uniformly composed 

 by two crystalline substances which present similarity in crystalline 

 form as well as of chemical composition" or as coloring matter in 

 mineral salts. 



The significance of the possibilities of solutions should be grasped 

 to understand the changes taking place in protoplasm through meta- 

 bolism, egestion and ingestion. 



ELECTRICAL CONDUCTIVITY, IONIZATION AND DISSOCIATION 



When a salt as sodium chloride (NaCl) is dissolved in water it 

 undergoes dissociation or breaks up into atoms sodium (Na) and 

 chlorine (Cl). Each atom is made up of electrons some of which 

 constitute the center and are positively charged with electricity while 

 some are on the outside and are negatively charged with electricity. 

 These latter are more mobile, are not held so tenaciously, and are called 

 the valence electrons because they establish the valency of the atom. 

 These electrons could be regarded as the units of electric charge. If 

 sodium (Na) and chlorine (Cl) unite in the formation of sodium chloride 

 (NaCl) it appears to be by electric attraction. This may be due to the 

 transfer of valence electrons from one to the other or attributable 

 to the rearrangement of valence electrons within the atom thus creating 



