METABOLIC GRADIENTS IN AMOEBA 93 



stimulation, then we must add to the list of properties of living 

 matter a sort of psychic property which would be possessed by 

 the amoeba, and possibly by all matter (cf. Mathews, '16, p. 

 595). If on the other hand, one denies to protoplasm, even to 

 the thinking cells in the cerebral cortex of man, the capacity for 

 self-stimulation, or automaticity, then one must refer the ac- 

 tivities of the amoeba to present or past conditions in its environ- 

 ment, and to internal conditions evoked by environmental 

 changes. In this connection it is interesting to note the great 

 tendency of the amoeba to bring into action again pseudopodia 

 which had been abandoned rather than to form new ones, — an 

 illustration of the effect of past conditions in determining present 

 behavior. 



A number of researches demonstrate that the nucleus plays an 

 important role in amoeboid movement. It has been generally 

 found that non-nucleated pieces of amoeba are incapable of nor- 

 mal amoeboid locomotion; they assume a spherical form, and 

 undergo slight changes of shape with the formation of short 

 broad pseudopodia but appear to be unable to form long pseudo- 

 podia or to attach them in the usual way. Details of the be- 

 havior with references to earlier work will be found in Willis ('16), 

 with whose account I must agree completely. Mr Vernon Lynch, 

 of Johns Hopkins University, kindly allows me to report that he 

 finds that non-nucleated pieces are generally more susceptible 

 to cyanide than nucleated ones, and always so if they formed the 

 anterior end of the amoeba at the time of cutting (pieces tested 

 one hour after cutting). It would be premature to attempt to 

 explain the role of the nucleus without further experimentation, 

 but I might suggest that the nucleus is concerned in the chemical 

 processes which underlie the alterations of physical state necessary 

 for locomotion. 



After I had developed the theory of amoeboid motion which 

 has been outlined in the preceding pages, I found that R. S. 

 Lillie had given a similar explanation for muscle contraction 

 ('06, '08, '12). He believes that the muscle fibril is a gel, the 

 anisotropic segments being more concentrated than the isotropic 



