COLLOIDS IN PROTOPLASM 



large molecules, some form aggregations of mole- 

 cules, others consist of small masses of the sus- 

 pended substance, others finally are but coarse 

 particles, already subjected to the force of gravi- 

 tation, and, if allowed, quietly deposit. The 

 particles, besides, may be of different physical 

 conditions, either liquid drops or solid bodies. 



Colloidal solutions, indeed, show quite a different 

 physical behaviour if the suspended particles 

 vary in size and in physical condition. In the 

 first case it is advisable to divide the colloidal 

 solutions into several groups according to the 

 solid or liquid state of the suspended particles. 

 Colloidal solutions which contain solid particles 

 may be called Suspensions, such as contain small 

 suspended drops of liquids may be named Emul- 

 sions. Instead of drops there may even occur in 

 colloids small bubbles of gas. Then the colloid 

 system more or less resembles froth. It is possible 

 that even in protoplasm small bubbles of gas are 

 included, forming a very fine foam. 



According to the size of the suspended particles, 

 all these colloids show well-marked physical 

 differences. When the particles are comparatively 

 large the constitution of the system is as a rule 

 very unstable, and the particles are inclined to 

 deposit. Such suspensions are scarcely to be con- 

 sidered as colloidal systems, but rather as a transi- 

 tion stage to colloids. Protoplasm must to a 

 certain extent have the properties of such a sus- 

 27 



