48 PROTOPLASM OF PROTOZOA 



has become relatively fluid, because only a liquid immiscible with the 

 surrounding medium shows the globular form which is essential in the 

 principle of minimal surfaces. This change in consistency may be 

 brought about by mechanical agitation (Chambers, 1921) and has been 

 experimentally studied by Angerer (1936), who presents data to show 

 that mechanical agitation of amoebae causes a decrease in viscosity in the 

 plasmagel [A. proteus) and an initial decrease followed by an in- 

 crease in viscosity in the plasmasol [A. duhid) . Extreme mechanical 

 agitation according to Angerer, leads to a minimum viscosity of the 

 plasmagel, which is eventually followed by the disintegration of the 

 organism, the substance of which mixes with the surrounding medium. 



If enough pressure is applied to the cover glass, the amoeba will 

 burst, and it may be observed, providing the injury is not too extensive, 

 that an effort is made on the part of the protoplasm at the region of 

 rupture to form a water-insoluble membrane, thus inhibiting further 

 mixing of the protoplasm with the water. This process has been re- 

 cently termed "the surface precipitation reaction" by Heilbrunn (1928). 

 If, however, the injury has been sufficient so that the interphase be- 

 tween the ruptured protoplasm and the surrounding medium is too 

 great, the surface precipitation reaction is not sufficient to prevent a 

 complete dissolution of the amoeba into the water. 



Small hemispheres of clear protoplasm (the incipient pseudopodia) 

 usually appear quickly upon the surface of a quiescent spheroidal 

 amoeba in the form of liquid extrusions from the main mass of proto- 

 plasm. Into these extrusions, which gelate equatorially, a central flow 

 of granular protoplasm may be seen streaming forward from the amoeba 

 in the direction of the advancing pseudopodium, which constantly moves 

 distally. As the pseudopodium advances, it may be seen to consist of an 

 outer cylinder of motionless protoplasm and an inner streaming fluid 

 protoplasm. That the cortical layer is gelated is indicated by the fact 

 that its granules and other inclusions are stationary. As the central 

 stream of flowing protoplasm (endoplasm or plasmasol) reaches the 

 hyaline cap, it moves peripherally in all directions and gelates (i.e., 

 becomes ectoplasm or plasmagel). At the other end of the amoeba the 

 plasmagel becomes plasmasol and passes forward as a fluid core through 

 the cylinder of plasmagel (Mast, 1926). The cause of the forward 

 flow of protoplasm is obscure, but the suggestion has been made by 



