84 AMEBOID MOVEMENT 



produced a lowering of the surface tension of the ameba thus 

 causing the ameba to flow around it ('98, p. 207). Subsequently, 

 however, he ('14) came to the conclusion that many amebas 

 cannot have fluid surfaces as usually understood, since they do not 

 spread as a film over water when they come into contact with 

 the surface. From this and other observations Rhumbler con- 

 cluded ('14, pp. 501-514) that the surfaces of amebas are not to 

 be compared with surface tension films on drops of inert simple 

 fluids ; but with the surface films of emulsions which take on the 

 properties of a solid. Since the question of ameboid movement 

 is not especially discussed in this later paper, it may be assumed 

 that in this respect his ('98, '10) earlier views have not been 

 materially modified. Rhumbler has suggested a great many phys- 

 ical models for the explanation of various ameboid activities such 

 as feeding, defecation, movement and so forth. 



In general agreement with Biitschli and Rhumbler were Ver- 

 worn ('92), Blochmann ('94), Bernstein ('oo), Jensen ('01, '02), 

 and recently Hirschfeld ('09) and McClendon ('12). All these 

 authors held that ameboid movement is a surface tension phenom- 

 enon. The application of the surface tension theory in explain- 

 ing ameboid movement demands a fluid surface and a fluid in- 

 terior and it is perhaps unnecessary to add that Biitschli, Rhumb- 

 ler and the others mentioned held that the protoplasm is fluid. 

 The question as to whether protoplasm is a fluid or possessed of 

 an internal structure was however hotly debated and we find 

 Fleming ('96), Heidenhain ('98), Klemensievicz ('98), Bellin- 

 ger ('06) and others opposing the group of authors just men- 

 tioned, by contending that the streaming protoplasm must have 

 some kind of structure. This question no longer concerns us 

 however, owing to our rapidly increasing knowledge of colloidal 

 solutions, for it is undoubtedly correct to hold that protoplasm is 

 colloidal. 



We have already insisted (p. 46) that the problem of ameboid 

 movement is made more difficult by narrowing it down to the 

 movements of ameba, and that to see the problem in its fullest 

 aspect requires consideration of streaming protoplasm wherever 

 found. Now it happens that there is in certain respects greater 

 diversity of streaming to be found in plant cells than in animal 



