180 PHYSIOLOGY OF MICROORGANISMS 



abundant precipitate. We have therefore to distinguish the viscous, 

 gelatinizing, colloidal mixtures, not coagulated by salts, from the non- 

 viscous, non-gelatinizing, but readily coagulable mixtures. The 

 former class I shall designate colloidal solutions, the latter colloidal 

 suspensions" Other divisions of much the same character have been 

 suggested. All lack in fundamental significance. They follow much 

 the same cleavage line but it possesses a ragged fringe. Whether of 

 great or permanent value or not, it is useful until a more definite, basic- 

 ally sound, division can be established. 



Colloidal solutions may exist in which the disperse phase may be 

 found in other dispersion means than water. These with water are 

 generally known as sols. When the dispersion means is water, the so- 

 lution or suspension is specifically called hydrosol; in alcohol, alcosol; 

 in glycerol, glycersol; etc. If the disperse phase takes up a certain 

 amount of water, it may enter into a jelly-like condition when it is 

 generally called a gel. In this instance, it would be called specifically 

 a hydrogel. It is possible to have as well alcogels, sulphogels, etc. 

 Gelatin may exist in a colloidal solution as a hydrosol and also as 

 a hydrogel depending upon the amount of water employed. There 

 also always exists the possibility of the disperse phase taking up 

 some of the dispersion means and the dispersion means actually in- 

 corporating some of the disperse phase. To what extent this may 

 be carried is problematical. 



It has already been indicated that colloidal solutions differ from 

 crystalloidal. The crystalloidal solutions are true molecular or ionic 

 solutions. The molecule may or may not divide into ions. Sodium 

 chloride passing into solution breaks into ions carrying with them 

 a positive and negative electric charge which in turn create a cur- 

 rent of electricity. The cane sugar molecule on the other hand does 

 not break up but goes into a molecular solution; there are no positive 

 and negative ions, consequently no electric dissociation. Substances 

 which ionize as sodium chloride are called electrolytes while substances 

 as cane sugar are non-electrolytes because they do not ionize. The 

 colloids, too, like sugar, are non-electrolytes and do not ionize, yet they 

 respond to a current of electricity passed through a solution. The 

 particles of a colloid have a tendency to pass to one pole or the other 

 depending upon the nature of the colloid. This reaction is called 

 electro phoresis. Further, it may be said that, if colloids pass toward 



