414 THE COLLOIDAL STATE 



It was not until recent years that, by the aid of the ultra- 

 microscope * with dark ground illumination and the methods 

 of microdissection, t a clearer knowledge of protoplasmic 

 structure has been gained. 



The structure of protoplasm is not constant ; not only 

 does it vary in different plants, but in the same plant and in 

 the same cell according to varying conditions. It is a complex 

 of colloids, the continuous phase of which is more or less 

 viscous, which can change spontaneously from the hydrosol 

 to the hydrogel condition, and vice versa. It has already been 

 stated that the Brownian movement of suspended particles 

 ceases in the gel state owing to the high viscosity. Gaidukov $ 

 noticed that when the streaming of the protoplasm in the 

 cells of Vallisneria temporarily stopped, only few of the 

 particles showed Brownian movement. In time the Brownian 

 movement became manifest, and as it increased the stream- 

 ing of the protoplasm began. Also Bayliss § comments on the 

 stopping of Brownian movement in amceba when the cytoplasm 

 is subjected to an electric shock too weak to be fatal, presum- 

 ably owing to a temporary change of state from sol to gel. 



The particles in the hydrosol vary much in size, ranging 

 from microsomes just visible under the high power with 

 transmitted light, to submicrons only to be seen under the 

 ultramicroscope. Suspended particles also may be present, 

 graded in size and showing Brownian movement, the rate of 

 which is determined by their size and the degree of viscosity 

 of the medium. These particles tend to increase in number 

 with the age and decreasing vitality of the cell. According to 

 Price the hydrosol complex is always emulsoid in character 

 but in varying degrees ; the protoplasm of the hairs of 



* Gaidukov : " Ber. deut. hot. Gesells.," 1906, 24, 107, 155, 192, 581 ; 

 " Dunkelfeldbeleuchtung u. Ultramikroskopie . . .," Jena, 1910. Price: 

 " Ann. Bot.," 1914. 28, 601. 



t Chambers : " Amer. Journ. Physiol.," 1917, 43, i ; " Biol. Bull.," 

 1918, 4, 121 ; " Trans. Roy. Soc. Canada," 1918, 12, 41 ; " Amer. Nat.," 

 1926, 60, 105. Seifriz : " Biol. Bull.," 1918, 34, 307 ; " Bot. Gaz.." 1920, 

 70, 360; "Ann. Bot.," 1921, 35, 269; "Amer. Nat.," 1926, 60, 124. 

 See also Heilbrunn : " Amer. Nat.," 1926, 60, 143 ; and Mast : id., 133. 



X Gaidukov : " Dunkelfeldbeleuchtung u. Ultramikroscopie in der 

 BioLogie und in der Medizin," Jena, 1910. 



§ Bayliss : " Principles of General Phj^siology," London, 1918. 



