82 PROTOPLASM OF PROTOZOA 



dase is apparently associated with the cytoplasmic matrix, independent of 

 all cytoplasmic constituents which could be stratified by centrifugal ac- 

 celeration. 



Optical Properties 



The ordinary optical characteristics of protoplasm, such as its trans- 

 parency, color, and refractive index, do not seem to be of very great im- 

 portance except that the observation of living protoplasm is conditioned 

 by these properties. Too many have assumed that because a structure 

 cannot be seen in living protoplasm, it is therefore nonexistent. 



TRANSPARENCY 



The ■ protoplasm of the protozoan cell is generally transparent or 

 translucent, but in the presence of granular or other inclusions it may 

 appear to be opaque or nearly so. Many of the differentiations are so 

 nearly of the same index of refraction that special fixing and staining 

 methods are necessary in order to study them. The state of aggregation 

 of the colloids of the general protoplasm seems to be dependent, at least 

 to some extent, on the salt content of the surrounding medium. Thus 

 Actinophrys sol in sea water is densely granular, while in fresh water it is 

 alveolar and translucent (Gruber, 1889). Spek (1921) has shown that 

 Actinosphaerium becomes relatively opaque in certain salt solutions, and 

 that P. bursaria, which is glass-clear, becomes dark brown in artificial salt 

 solutions, owing to the collection of albuminoid substances into large 

 aggregates. Certain observations of Schaeffer (1926) on marine Amoebae 

 are of interest here: Flabellula pellucida, a most transparent marine 

 amoeba, becomes densely granular in 2 5 -percent sea water, while F. 

 cHata, another marine amoeba, is unusually transparent in 364-percent sea 

 water. 



COLOR 



Protoplasm is usually observed to be colorless or grayish; many of the 

 shades of blue, green, or yellow described for Amoebae are merely dif- 

 fraction phenomena or subjective in nature. The color of the endoplasm 

 of various amoebae has been described by Schaeffer (1926) as pale 

 bluish-green, yellowish-green, bluish-gray; Hyalodiscus elegans has endo- 

 plasm which is cirange-yellow centrally and ashen-gray peripherally. The 



