172 BIOLOGY OF THE PROTOZOA 



podia formation or by the elements of flagellum, cilium or myo- 

 neme, is a matter of pure speculation. The reactions which char- 

 acterize the resulting movements, however, can be analyzed and 

 measured and these form the chief basis of our knowledge of pro- 

 tozoan irritability. Attempts to explain pseudopodia formation 

 and amoeboid movement have ^■a^ied with the changes in our con- 

 ceptions of the physical make-up of protoplasm. The protoplasm 

 of Amceha regarded as a fluid substance, was supposed to follow 

 the laws of surface tension characteristic of all fluids. Pseudopodia 

 formation, according to the views of Berthold (188(j) is the attempt 

 of one fluid (proto])lasm) to spread out between water and the 

 substratum as Quincke's well-known experiments demonstrated for 

 fluids. As physical conditions on all sides of the Amoeba are not 

 equal, variations in tension result in local dimiiuition, and the ten- 

 dency' to spread is focused in a local area and the pseudopodium 

 results. Biitschli's (1894) observations and exj)eriments with emul- 

 sions of oil, salts and water, and Rhumbler's (1898) analysis of the 

 causes of movement in lobose rhizopods led these observers also to 

 interpret pseudopodia formation as a result of surface tension 

 phenomena. With the more modern conception of protoplasm as 

 a colloidal aggregate in the physical state of an emulsion in which 

 the external and internal i)rotoplasm of Amoeba are in the relation 

 of gel and sol, the difficulty of applying the laws of fluids became 

 apparent and the hypothesis based upon surface tension has been 

 generally abandoned. Rhumbler himself (1910 and 1914) recog- 

 nized this difficulty and materially changed his conception of amoe- 

 boid movement, while Hyman (1917) greatly enlarged and perfected 

 his later point of view. According to Hyman the ectoplasm of 

 Amoeba, by virtue of its relatively solid state, becomes tenuous but 

 elastic, as demonstrated by the experiments and observations of 

 Jennings (1904), Kite (1913, Schultz (1915) and Chambers (1915, 

 1917), and exerts an elastic tension on the inner fluid protoplasm. 

 Bancroft (1913) and Clowes (191G) demonstrated the reversibility 

 of phase in diphasic jjhysical systems through the agency of electro- 

 lytes, and the conclusion followed that the ectoplasm represents a 

 reversal phase of the more fluid inner protoplasm. Hyman argues 

 that, owing to the tension of the enveloping ectoplasm, if any local 

 region of the solid ectoplasm becomes liquefied, the resistance gives 

 way at such a point and the fluid endo})lasm is pressed out, thus 

 forming a pseudopodium. The immediate cause of such liquefac- 

 tion she traces to a local increase of, or change in, metalx)lic activity 

 resulting in the production of hydrogen-ions apjiropriate for dis- 

 solution of the solid ectoplasm. By use of Child's potassium cyanide 

 test for metabolic gradients, she was able to demonstrate that such 

 local regions of greater metabolic activity actually occur on the 

 periphery of Amoeba proteus before a pseudopodium breaks out, also 



