PROTOPLASM OF PROTOZOA 83 



contents of the contractile vacuole are often slightly pink. This may be 

 regarded as an optical illusion, since the color observed is complementary 

 to the usual bluish-green of the endoplasm. Very frequently the color 

 is obscured by the presence of colored inclusions of various kinds, or 

 caused by colored inclusions of the same index of refraction as the proto- 

 plasm and therefore difficult to differentiate. 



Ciliates may be colorless, gray, pink, blue, or violet. The blue color 

 of 5". coeruleus is caused by a coloring matter, called stentorin, diffused 

 through the cytoplasm, but in Blepharhma the color, which may vary 

 from none through pink and violet to purple, and varies with the cul- 

 tural conditions and from individual to individual in the same culture, 

 \s apparently concentrated in the pellicle (Nadler, 1929). According 

 to Jennings (1906), most colorless Infusoria do not react at all to a 

 light of ordinary intensity; this has not been tested with forms such as 

 Blepharhma, in which the color varies. 



In the plant-like flagellates color is usually caused by chromatophores, 

 which may be green, blue (Lackey, 1936), brown, or yellow. The most 

 interesting colored inclusion is the hematochrome, found in such forms 

 as E. rubra as red granules from 0.3 to 0.5 microns in diameter. These 

 euglenae form a green scum in shaded places; the green chloroplasts 

 mask the hematochrome, which is centrally located; in direct sunlight the 

 scum is red, the hematochrome being peripherally located and masking 

 the chloroplasts. Control of the distribution of the hematochrome is so 

 delicately balanced that if the euglenae are shaded for fifteen minutes, 

 they change from red to green (Johnson, 1939). The mechanics of 

 this control needs to be investigated. 



REFRACTIVE INDEX 



Even the finest strands of protoplasm can be seen in water, in spite 

 of the fact that they may be transparent and colorless. This is because 

 of their relatively high index of refraction. It is surprising that so little 

 is known about the optical characters of protoplasm which may be seen 

 to change during cell division. Schaeffer (1926) has shown that the 

 nuclei of certain marine amoebae become much more prominent by dilu- 

 tion of the sea water with fresh water, and Chalkley (1935) has shown 

 that there is a change in the refractive index of the nuclei of A. pro tens 

 during division: the interkinetic nuclei can easily be seen at a magnifica- 



