'46 S. O. MAST AND F. M. BOOT 



as high as that of molten platinum, the highest yet discovered. 

 But the surface tension of protoplasm is, according to Czapek as 

 previously stated, only approximately 50 dynes per centimeter 

 and with a surface tension of this magnitude in ameba it is ques- 

 tionable whether a greater local reduction than 25 dynes per 

 centimeter could be produced without destroying the organisms. 

 It is therefore evident that surface tension plays a very insig- 

 nificant role in the process of feeding described unless the proto- 

 plasm of these organisms consists of some sort of a structure that 

 makes possible a great magnification of the effect of the surface 

 tension. But since there is no evidence of such a structure the 

 required power must, for the present, be sought largely in con- 

 nection with other phenomena, gelation pressure, absorption 

 pressure, adhesion, cohesion, diffusion, etc. 



There is as yet little or no experimental evidence which di- 

 rectly bears upon the relative importance of these different fac- 

 tors or upon the mechanics of their regulation, although it is 

 clear that the reactions in Ameba do not depend solely upon 

 changes in the environment. Movement and changes in move- 

 ment (responses) may undoubtedly occur without any affective 

 external changes, such responses being entirely due to internal 

 processes. It is also obvious that while some of the responses 

 which are dependent upon external conditions are directly re- 

 lated to the environment, being local responses to local stimula- 

 tion, others are not; and we are unable to conceive how some of 

 the latter can be explained without assuming that the entire 

 animals are involved as organized systems of considerable com- 

 plexity, that there are impulses transmitted from one part of the 

 body to another and that there is a regulatory center, in which 

 impulses may originate and in which those originating elsewhere 

 may be modified and controlled. This is especially true regard- 

 ing much that occurs in the process of feeding on rotifers. It is 

 also true regarding the peculiar mushroom-shape assumed when 

 feeding on infusoria and regarding a considerable number of 

 responses described by Jennings (^04), Kepner and Taliaferro 

 ('13) and others. Moreover, the facts that enucleated parts of 

 ameba do not respond at all or respond in a haphazard fashion, 



