X. THE CHANGE OF PROTOPLASM STRUCTURE 305 



under the influence of various effects. It may only be natural, there- 

 fore, that such a change is sometimes revealed as the movement of 

 organisms. 



Amoeboid movement is said to be established by the sol-gel change 

 of the protoplasm (143), thereby amoeba can move in pulsatory motion 

 (144). If we assume that the protoplasm protein in amoeba are usually 

 in a state somewhat contracted and that both the extension and 

 contraction of the protein threads tend to occur too far, not exactly re- 

 sponding to the degree of the stimuli causing the change, the amoe- 

 boid movement can be easily explained. Thus, when a stimulus which 

 may cause the extension of the protein threads is given at a site of the 

 protozoan, the protein molecules at the site will be extended with the 

 projection of the protoplasm, but as this extension may go too far, a 

 compensatory contraction will follow. This contraction likewise may 

 occur excessively, spreading to other proteins, with the successive 

 coagulation of protoplasm into elementary particles ; combining force 

 between the proteins may then be increased and the coagulated elemen- 

 tary bodies will be attracted and drifted towards the site of the stimulus. 

 If the stimulus extending the protein continues to be applied to the 

 same site, the protein in the coagulated particles, thus attracted to 

 the site, will be extended, and the protoplasm will be projected, followed 

 by the contraction of the protein and subsequently by the gathering 

 of coagulated particles. 



On the contrar>% if a stimulus causing a contraction is applied, 

 the protein molecules at the site of the stimulus may undergo con- 

 traction, which may spread to the opposite side, where no contracting 

 stimulus is present, so that soon the extension will follow at this 

 side, with the projection of protoplasm. But this extension may be 

 temporary if contracting stimulus continues to exist, so that contration 

 may follow which will attract the coagulated particles to the side 

 where no stimulus exists, as a result the protozoan can move to 

 escape the stimulus as shown in Fig. 29. 



If the protoplasm protein is stretched by the benevolent stimulus 

 and contracted by the detrimental one, the movement will be said 

 purposeful and the organisms having the protein of such a property 

 can continue existence and well prosper. Since intense and unusual, 

 physical or chemical stimuli generally cause the protein to coagulate 

 or to contract, it should naturally follow that organisms will achieve 

 the movement to get rid of such stimuli. However, occasionally the 

 same stimulus may give rise to the different reactions among varying 

 organisms, indicating that some stimulus is favourable for some 

 organisms but unfavourable for others. The property to achieve such 

 a purposeful movement must have been raised because only the 



