84 PROTOPLASM OF PROTOZOA 



tion of 200 diameters; those in division cannot. Very few measurements 

 of the refractive index of protoplasm have been made; Frederikse 

 (1933b) has reported a value of 1.40 to 1.45 for A. verrucosa; Mackin- 

 non and Vies (1908) 1.51 for the cilia of Stentor, and 1.56 for the 

 flagellum of Trypanosoma [Sphochaeta) halhiani. Mackinnon and Vies 

 made their determinations by immersing the organisms in media of 

 different refractive indices; double refraction, due to depolarization, 

 disappears in media of the same refractive index as the cilia and flagella. 

 Faure-Fremiet (1929) found the index of refraction for entire amoebo- 

 cytes of Lumhricus to be 1.400, for the hyaloplasm 1.364; of Asterias 

 to be 1.446 and 1.385 respectively (for methods see Pfeiffer, 1931). 



Structural Properties 



It has long been known that the polarity of a cell may persist after 

 the relative positions of its various visible constituents have been changed; 

 this has led to the idea that polarity has its basis somehow or other in 

 the structure of homogenous cytoplasm, which remains unchanged in 

 spite of exposure to high centrifugal forces (Conklin, 1924), Polarity 

 and symmetry are generally present in the Mastigophora and Infusoria, 

 in which an anterior-posterior axis is usually persistent throughout active 

 life, and has been described as present in cysts (Lund, 1917, in Bursar/a) . 

 However, in Sarcodina such as Amoeba, polarity may be thought of as 

 continually changing, being bound up with the gel-sol process at the 

 temporary posterior end, the flow of protoplasm forward, and the sol- 

 gel process at the temporary anterior end. Hyman (1917) has demon- 

 strated that the temporarily differentiated anterior end of Amoeba is the 

 region of highest susceptibility to cyanide. Mast (1931) and others 

 have reported that electrical currents have a solating action on the 

 plasmagel, on the side directed toward the cathode. 



Recently Chalkley (1935) has studied the process of cytokinesis in 

 A. proteus. He observed, with the onset of prophase, a loss in sensitivity, 

 a swelling up of the organism, a decrease in activity of the contractile 

 vacuole, and an increase in movement of the granules in the region 

 of the nucleus. With the separation of the daughter chromosome plates, 

 he observed a flow of the cytoplasm from the equator, in the same direc- 

 tion as the separating daughter plates. As the daughter plates approach 

 the surface of the cell and the new nuclei begin to form, a solation of 



