THE CELL ASTER 487 



are free of visible granules which appear only as the eggs grow 

 when they accumulate until the egg substance is crowded 

 with them (Wilson, '99). That the hyaloplasm is really hetero- 

 geneous in structure, although under ordinary microscopic 

 examination it appears homogeneous, can be demonstrated if, 

 instead of using transmitted light, the hyaloplasm be illuminated 

 by a beam of light striking it from the side only. The presence 

 of minute particles large enough to intercept and scatter the 

 light rays are then revealed through the production of a cone- 

 shaped beam of light known as the Faraday or Tyndall phenom- 

 enon. ^ If the particles are not resolvable (in which case they 

 are known as amicrons) a hazy light is all that can be seen. If, 

 however, the particles are large enough (when they are known 

 as submicrons) they appear to the observer as shining spots 

 dispersed throughout a transparent medium. In the liquid 

 hyaloplasm, these particles exhibit active Brownian movement 

 (Gaidukov, '10, Marinesco, '12, Price, '14). In coagulated 

 hyaloplasm they are motionless. 



Because of its ultra-microscopic heterogeneity in structure, 

 we speak of protoplasm or hyaloplasm as existing in the colloid 

 state tf> distinguish it from 'crystalloid' or true solutions, whose 

 ingredients are too small to disperse light rays of visible wave 

 lengths, and from true solids in which no Brownian movement is 

 discernible. In a colloid solution the dispersed particles con- 

 stitute the internal or dispersed phase and the liquid in which 

 they are suspended is the external phase or dispersion-medium. 



Of the two great classes of colloidal solutions, the class con- 

 sisting of emulsion colloids^ is of chief interest in biological phe- 

 nomena. To this class belong all the colloids obtainable from 

 organic matter, such as gelatin, glue, albumen and starch. They 

 are colloids in which both phases may be liquid, the internal phase 



2 The Faraday phenomenon is the principle upon which the ultramicroscope 

 is based. 



^ The other class is that of the suspension colloids in which the dispersed phase 

 consists of solid particles suspended in a liquid dispersion-medium. Suspension 

 colloids have no viscosity and do not, as a rule, undergo gelation. Their two 

 phases are comparatively easy to separate and they are readily coagulated with 

 salts. Examples of this class are the metallic suspension-colloids orsuspensoids. 



