PROTOPLASM OF PROTOZOA 47 



The granular region of an amoeba is made up of an outer stationary 

 layer, which forms a hollow cylinder through which an axial stream of 

 protoplasm flows. The outer stationary layer has been called the ecto- 

 plasm and, more recently, because of its firm consistency, plasmagel; 

 the axial flowing layer, endoplasm, and, more recently, because of its 

 fluid consistency, plasmasol. More difficult to observe, because of its 

 extreme thinness, is the surface layer, or plasmalemma, just external to 

 the clear hyaline layer. 



Ordinary methods of fixation often result in an apparent loss of the 

 constituents which may be seen in the living cell; however, by the use 

 of suitable fixing methods Mast and Doyle (1935a) were able to show 

 that in A. pro tens the cytoplasmic constituents may be preserved in a 

 form scarcely distinguishable from the living condition, except for the 

 nuclear granules and the water-soluble salts. Since protoplasm is an un- 

 stable intimate association of salts in solution, proteins, fats, and other 

 materials which may give it a fibrillar or an alveolar appearance, we 

 cannot hope to preserve it unchanged. Indeed, we may not even ob- 

 serve it in the living condition unchanged, as change is a universal 

 characteristic of protoplasm. It must be constantly kept in mind that 

 what is observed in a permanent fixed preparation is not living material, 

 but likewise it must also be recognized that while the fixed material is 

 not protoplasm, it is at least a significant artifact derived from proto- 

 plasm, since it has had its origin in the coagulation of proteins and 

 other significant elements of living material. Most of the established 

 facts of cytology have been first observed in fixed material, and later 

 corroborated by a study of the living. However, it should be pointed 

 out, from the works of Hardy and of Fisher, that probably many of 

 the older theories of protoplasmic structure, such as the granular, fibril- 

 lar, alveolar, and reticular, have been based in part, at least, on artifacts 

 induced by the methods employed. 



Probably the most significant feature of the protoplasm of Amoeba 

 is its ability to change from a relatively fluid state to a more solid jelly- 

 like condition. Upon mechanical agitation, such as occurs in trans- 

 ferring an amoeba to a slide or by tapping on the slide, the organism 

 may assume a globular form which may have short projecting pseudo- 

 podia. If the temperature be raised to 30° C, the projections may dis- 

 appear (K. Gruber, 1912). This means that the protoplasm present 



