CHAPTER VI 

 THE COLLOIDAL STATE 



Protoplasm consists essentially of three types of systems — a 

 true solution (molecular dispersion) of salts, carbohydrates, and 

 other water-soluble substances; an emulsion of fats and like 

 matter; and a dispersion of organic substances, mostly proteins, 

 which form jellies. The last two types of systems are colloidal. 

 While it is impossible to attribute more or less importance to any 

 one necessary substance or system in protoplasm, yet it is true 

 that those substances which are colloidal, such as the fats and 

 the proteins, possess properties which particularly characterize 

 living matter. This is especially true of the proteins and the 

 colloidal systems (jellies) that they form. It is thus obvious 

 that a knowledge of the colloidal state of matter becomes exceed- 

 ingly important to the study of protoplasm. 



Characterization of the Colloidal State. — Matter is said to be 

 in the colloidal state when it is permanently dispersed and so 

 finely so that the individual particles, though larger than mole- 

 cules, cannot be seen. The water of the Mississippi River is 

 forever muddy because the clay particles contained in it are so 

 small that they do not readily settle until they meet the salts of 

 the sea, when they quickly fall and form the Mississippi delta. 

 Both the suspension of the finely divided clay particles in the 

 river water and their precipitation by the salts of the sea are 

 colloidal phenomena. A threatening cloud is made up of drop- 

 lets of water finely dispersed and in (relatively) permanent sus- 

 pension in the air; the water is in the colloidal state. When 

 the droplets, through coalescence, become too large, they fall 

 as rain. The tails of comets consist of particles so small that 

 when our earth sweeps through them we see nothing of them, 

 yet illuminated against the black background of the night sky 

 they become brilliant. The cosmic particles of the comet's tail 

 are in the colloidal state, and their luminosity is due to the 

 scattering of light, a colloidal phenomenon. The blue color of 



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