228 INFLAMMATION 



the great family of amebse. Some of them are branching, some 

 are fixed in extension, some have a stiff elastic axis. It would 

 also be difficult to explain cilia as produced by changes in sur- 

 face tension, yet we find in some protozoa that pseudopodia may 

 take on the persistence and action of cilia, and that cilia may 

 seem to change into pseudopodia. Jennings has made a most 

 extended study of the relations of the " Behavior of Lower 

 Organisms " 1 to the physical theories of ameboid motion, and 

 is unable to corroborate the claim that the processes that go on 

 in " artificial amebse " exactly reproduce those of living ame- 

 bse, or to accept the statement that living protoplasm behaves 

 exactly as any similar drop of fluid would under the same con- 

 dition. He states that the currents set up in artificial amebse 

 by changes in surface tension are not the same as those in living 

 ameba, contrary to Rhumbler and to Biitschli. The move- 

 ment of ameba, he maintains, is not due to the flowing of the 

 contents of the cell in a central, axial current out into the 

 pseudopodium and back on the sides, as occurs in the artificial 

 ameba ; but rather to a rolling forward of the upper surface 

 over the anterior edge to the lower surface, where it becomes 

 fixed to the surface on which the ameba is crawling. The part 

 played by surface tension, he claims, is in the case of amebse a 

 very subordinate one, and it is not sufficient to explain the 

 movements of the living cell. 



However the discussion concerning the amebse may turn, it 

 must be appreciated that there are some important differences 

 between even the ameba and the leucocyte. The latter has by 

 far the simpler organization, and approaches in structure, and 

 presumably, therefore, also in response to stimuli, more closely 

 to the simple drop of colloid matter. It has no pulsating 

 vacuoles, no specialized pseudopodia, never forms shells or 

 coverings, and does not conjugate as do the amebse. The ex- 

 ternal surface of the leucocyte is much simpler, an important 

 fact in connection with surface tension effects, for in the leuco- 

 cyte the surface seems to be practically un differentiated, naked 

 protoplasm ; whereas in ameba it is formed of a well -differentiated 

 " ectosarc, " which has marked motile powers, being able to 

 contract sufficiently to cut an injured ameba completely in two. 

 At the very least the surface tension explanation of leucocytic 

 action agrees perfectly ivith most of the observed actions of leuco- 

 cytes, and it is the only reasonable theory offered. There seems 

 to be no middle ground between such a physical theory and a 



1 Publication No. 16, Carnegie Institute, Washington, 1904; also see Amer- 

 ican Naturalist, 1904 (38), 625. 



