264 INFLAMMATION 



outside and inside the body; these substances are chemotactic because 

 they influence the surface tension of the leucocytes, and since with 

 most if not all the products of cell disintegration the effect is to lower 

 surface tension, the chemotactic effect is positive. As the chemotactic 

 substances are produced, they diffuse through the tissues until they 

 reach the walls of a capillary, through which thej'- begin to pass, pre- 

 sumably most rapidly through the thinnest parts of the wall, the 

 "stomata" and intercellular substance. The leucocytes passing along 

 in the bore of the capillary will be touched by the chemotactic sub- 

 stances most on the side from which the substances diffuse; the sur- 

 face tension will be lowered on this side, causing the formation of 

 pseudopodia and motion in this direction. When the leucocytes come 

 in contact with the wall, their surfaces, because saturated with the 

 chemotactic substances, will have a tension much the same as that 

 of the cells of the capillary wall, which are likewise saturated with the 

 same substances, 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 be- 

 have as if either they or the capillary wall had become sticky."^" Sur- 

 face tension of the leucocytes will be least nearest the points where the 

 most chemotactic substances are entering the capillary, namely, the 

 stomata; hence the pseudopodia 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 

 migration, 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 dichro- 

 mate, 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 phago- 

 cytosis. The motion of the leucocyte will continue in a forward di- 

 rection 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, {b) It may 

 r(;a(;h a material that exerts a marked jiositivo iiithience upon it, 

 causing much lowering of the surface tension, ])ul which is so large 



*" Kr('il)i(!li (An^h. f. Dcrin.atol., 1912 (114), SS.")) describes as chemical changes 

 in the vessel walls during; the early stages of inflammation, a diffuse sudanophile 

 change throughout the endothelial cells, in the form of fine, dust-like particles. 

 Probably this change dei)ends simply on an aggregation of the intracellular lipoids. 



