THEORIES OF CHEMOTAXIS AND PHAGOCYTOSIS 227 



more abundant than is the leucocyte, e. g., tuberculosis and 

 other chronic inflammations. The cells that fuse about an in- 

 fected catgut ligature are the leucocytes, for they are most 

 abundant in such a place.) A good illustration, also, is the 

 giant-cell formed by fusing of leucocytes about blastomyces in 

 minute abscesses in the epithelium in blastomycetic dermatitis ; 

 the epithelial cells cannot flow or coalesce well because of their 

 abundance of stiff keratin and their specialized cell-wall, and 

 hence do not participate ; the leucocytes are individually too 

 small to surround the fungus cells, and hence they flow about 

 them in the abscess exactly as they will do experimentally in a 

 test-tube or in a guinea-pig's abdomen (Hektoen). The forma- 

 tion of giant-cells is, on this ground, but an amplification of 

 ameboid movement and phagocytosis. The fusing of the in- 

 dividual cells is due to the lowering of their surface tension by 

 the materials diffusing from the body which is to be absorbed, 

 until the surface of each cell becomes alike, when the surface 

 tension at the point where each cell is in contact becomes zero 

 and the cytoplasm runs together. 



Objections to the above Hypothesis. Physical ex- 

 planations of ameboid movement seem to fit very perfectly the 

 known facts concerning the actions of leucocytes. There arise 

 but a few difficulties in applying these laws to leucocytic action ; 

 one is the phagocytosis of chemically inert bodies, such as coal 

 particles, tattooing materials, stone dust, etc. We know that 

 amebse also may take up such inert materials, although they 

 generally refuse them, and it is believed that the particles exert 

 some local injury to the cell wall that leads to an alteration in 

 its tension. Amebae seem also sometimes to excrete a sticky 

 substance over their surfaces or over the foreign matter that is 

 to be engulfed, which excretion seems to be the result of surface 

 stimulation. Possibly leucocytes do the same. We must bear 

 in mind, however, that the protoplasmic cells have much greater 

 possibilities for action than the " artificial ameba," since within 

 the protoplasm countless chemical changes are going on which 

 must cause continual alteration in surface tension ; it is quite 

 possible that mere mechanical action may alter chemical action 

 at the point of contact, so that the injuring particle may become 

 surrounded through local liquefaction of the protoplasm. 



With the ameba, unfortunately, the explanation of all its 

 activities by purely physical analogies is apparently not so 

 successful. Although simple pseudopodia may be produced ex- 

 perimentally, and their formation explained readily on the sur- 

 face tension basis, yet we find many forms of pseudopodia in 



