SUPPURATION 207 



point of contact, so that the injurinj^ particle niaj' become surrounded throu^^h local 

 liquefaction of the protoplasm. 



With the aineba, unfortunately, the explanation of all its activities by purely 

 physical' analogies is apparently not so successful. iUthouKh simple pseudopodia 

 may be produced experimentally, and their formation explained readil}' on the 

 surface tension basis, yet we find many forms of pseudopodia in the great family 

 of ameba". Some of them are branching, some are fixed in extension, some have a 

 stiff elastic axis. It would also l)e difficult to explain cilia as produced by changes 

 in surface tension, yet we find in some protozoa tiiat pseudopodia may take on 

 the persistence and action of cilia, and that cilia may seem to change into pseudo- 

 podia. Jennings has made a most extended study of the relations of the "Be- 

 liavior of Lower Organisms"*' to the physical theories of ameboid motion, and is 

 unable to corroborate the claim that the processes that go on in "artificial ameba>" 

 exactly reproduce tliose of living ameba-, or to accept the statement that living 

 protoplasm behaves exactly as any similar drop of fluid would under the same 

 conditions. He states that the currents set up in artificial ameba- by changes 

 in surface tension are not the same as those in living ameba-, contrary to Rhumbler 

 and to Biitschli. The movement 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 for- 

 ward 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 ameba- a very sul)ordinate one, and it is 

 not sufficient to explain the movements of the living cell. 



However the discussion concerning the amebae 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 external surface of the leucocyte is much simpler, an 

 important fact in connection with surface tension effects, for in the 

 leucocyte the surface seems to be practically undifferentiated, naked 

 protoplasm; whereas in amebae 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 per- 

 fectly with most of the observed actions of leucocytes, and it is the only 

 reasonable theory offered. There seems to be no middle ground be- 

 tween such a physical theory and a metaphysical theor}^ which would 

 endow a single cell, without organs or nervous system, with the 

 reasoning powers of highly developed animals, a position incompati- 

 ble with the entire evidence of experience. 



SUPPURATION" 



For the formation of pus two conditions are necessary: (1) the ac- 

 cumulation of leucocytes, and (2) necrosis and liquefaction of cells 



** Publication No. 16, Carnegie Institute, Washington, 1904; also see American 

 Naturalist, 1904 (38), G25. 



*^ Inflammatory Exudates, their formation and composition, are considered in 

 Chapter xiv. 



