PROTOPLASM OF PROTOZOA 49 



Hyman (1917) and many others that it is due to the tension exerted 

 upon the fluid plasmasol by the elastic plasmagel. 



There has been much discussion concerning the physical characteristics 

 of the outermost layer, or plasmalemma, of different species of amoeba. 

 In certain forms, such as A. verrucosa, the pellicle may be lifted with 

 microdissection needles and stretched, apparently without injuring the 

 organism in any way (Rowland, 1924c). Seifriz (1936) also found 

 a thin outer membrane on A. proteus which was resistant, elastic, and 

 highly viscous except at the advancing tip of the pseudopodia. Likewise 

 Chambers (1924) was able to lift the plasmalemma in A. proteus by 

 injecting water beneath it, thus causing large blisters to form between 

 the plasmalemma and the underlying surface which burst upon punctur- 

 ing, leaving the pellicle collapsed. Mast (1926) caused blisters to 

 appear by local pressure; further pressure caused disruption of the 

 pellicle, the frayed ends of which were clearly observed. 



Practically all investigators are agreed that the plasmalemma moves 

 forward, at least on the upper surface of a moving amoeba. In addition, 

 the method of formation of new food vacuoles requires a structure 

 of the plasmalemma of such nature as to form new surfaces immediately 

 by the replacement of large areas of the plasmalemma which have been 

 used in forming the boundary of the food vacuoles (Schaefl^er, 1920). 



Immediately beneath the outer layer, or plasmalemma, is the clear 

 hyaline layer. That this layer is fluid may be shown by the fact that it 

 contains scattered granules which are in Brownian movement (Mast, 

 1926) and by the injection of a suspension of lamp black into it, the 

 injected lamp-black particles spreading throughout this clear hyaline 

 layer (Chambers, 1924). However, Schaeffer (1920) holds that some- 

 times it is more rigid than endoplasm, and at other times not. 



Colloidal Nature of Protoplasm 



Any attempt to understand the processes occurring in protoplasm 

 must depend for its success not only upon a knowledge of the chemical 

 constitution of protoplasm but also of its physical structure. For this 

 reason much ingenuity has been exercised in trying to discover the 

 physical structure of the protoplasm in such relatively simple forms as 

 Amoeba, in which permanently differentiated structures are at a mini- 

 mum. For example, in A. proteus apparently only the nucleus is perman- 



