PROTOPLASM OF PROTOZOA 51 



movement, and to chemical reactions in protoplasm. On the other hand, 

 solids have great internal cohesion of molecules, i.e., they retain their 

 shape, show elasticity; this is essential to the maintenance of continuity 

 and form of protoplasm. Colloids quite generally show changes from a 

 relatively fluid to a firm jelly-like consistency, so that protoplasm as a 

 colloidal system may partake of the nature of a solid (in the gel con- 

 dition) or that of liquid (in the sol condition). Thus changes in vis- 

 cosity are one of the essential factors in ameboid movement. In addi- 

 tion, the viscosity of the protoplasm as a whole, and particularly the 

 changes in viscosity within a given portion of a protozoan, are very 

 important factors to be considered in connection with a study of mitosis, 

 cytokinesis, cyclosis, rate of diffusion of various substances, protoplasmic 

 reorganization, and functioning of such organs as the contractile vacuole. 



Besides the qualitative methods of estimating the viscosity of proto- 

 plasm by observing the presence or absence of movement (Mast, 1926b) , 

 presence or absence of Brownian movement (Bayliss, 1920; Pekarek, 

 1930; Brinley, 1928), microdissection studies (Kite, 1913; C. V. Tay- 

 lor, 1920; Chambers, 1924; Howland, 1924c; and others), certain 

 experimental methods, i.e., centrifugation (Heilbrunn, 1928; 1929b; 

 Fetter, 1926), electromagnetic methods (Seifriz, 1936), and rate of 

 diffusion of certain dyestuffs (Chambers, 1924; Needham and Need- 

 ham, 1926) have been used to reveal data as to the relative and absolute 

 viscosity of the protoplasm of various Protozoa. For a detailed discus- 

 sion of these various methods the reader is referred to the works of 

 Chambers (1924), Heilbrunn (1928), and Seifriz (1936). 



The Protozoa show a wide range of viscosity values. In fact a varia- 

 tion in protoplasmic viscosity from 2 times that of water in Amoeba 

 (Heilbrunn, 1929b) to over 8,000 times that of water in Paramecium 

 (Fetter, 1926) has been reported. Undoubtedly a much higher viscosity 

 exists in many protozoan cysts and other forms characteristic of re- 

 sistant stages. Seifriz (1936) has reported that during the winter the 

 Plasmodium of a myxomycete becomes as hard and as brittle as a thin 

 sheet of dry gelatin. 



In addition to the information obtained about the consistency of 

 various Protozoa from multilation experiments, for example those of 

 Calkins (1911) and Peebles (1912) on Paramecium caudatum, the 



