THEORIES OF CHEMOTAXIS AND PHAGOCYTOSIS 225 



will have a tension much the same as that of the cells of the 

 capillary wall, which are likewise saturated with the same sut>- 

 stances, and the two surfaces will tend to cling to one another; 

 explaining the phenomenon of adhesion of leucocytes to the 

 capillary wall, when, according to the usual description, " the 

 leucocytes behave as if either they or the capillary wall had 

 become sticky." Surface tension of the leucocytes will be least 

 nearest the points where the most chemotactic substances are 

 entering the capillary, namely, the stomata ; hence the pseudo- 

 podia will form in this direction and flow through the openings, 

 the rest of the cytoplasm flowing after and dragging the nucleus 

 along in an apparently passive manner. Since it is the cytoplasm 

 that seems to be chiefly affected in these processes, the nucleus 

 appearing to be rendered inert by its relatively dense and fixed 

 structure, the leucocytes with most cytoplasm are most active in 

 emigration, while those with the least, the lymphocytes, are 

 affected relatively little or not at all. 



Once through the vessel wall, the motion continues in the same 

 manner, toward the side from which the chemotactic matter 

 comes, just as the mercury drop flows toward the crystal of 

 potassium dichromate, or the drop of oil flows toward the 

 alcohol. If the leucocyte meets a substance that lowers its 

 surface tension sufficiently, it will flow around the object and 

 enclose it, just as the chloroform drop flows about the piece 

 of shellac or balsam ; this constitutes phagocytosis. The motion 

 of the leucocyte will continue in a forward direction until one 

 of several possible things happens : (a) The leucocyte may 

 reach a point where the chemotactic substances are so thoroughly 

 diffused that the effects on its surface are the same on all sides ; 

 there will then be no tendency to move in any direction. (6) 

 It may reach a material that exerts a marked positive influence 

 upon it, causing much lowering of the surface tension, but 

 which is so large that the cytoplasm flowing along its surface 

 cannot surround it ; other leucocytes will experience the same 

 change, their cytoplasm will fuse together because of the equal 

 lowering of their surface tension, and soon we get a mass of 

 leucocytes with fused cytoplasm surrounding the object, forming 

 a " foreign body giant-cell." (c) The leucocyte may reach a 

 place where the concentration of the chemicals is so great that 

 chemical changes are produced in its cytoplasm. If these 

 changes are of a coagulative nature, the surface of the cell will 

 be stiffened so that it cannot migrate further ; if of a solvent 

 nature, the leucocyte is destroyed, (d) It may reach the margin 

 of an area where the preceding leucocytes have become coagu- 



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