224 INFLAMMATION 



of sand, or diatom shells, or other suitable particles. The par- 

 ticles are united so closely and fitted together so well that they 

 are almost perfectly free from crevices. Even this process is 

 accurately imitated in Rhurnbler's experiments. If a drop of 

 oil is mixed with fine grains of quartz sand, and dropped into 

 70 per cent, alcohol, the grains are thrown out to the surface, 

 where they adhere to the surface of the drop and to one another 

 exactly as do the particles in a difflugia shell. So well fitted 

 are the particles that the artificial shell may remain intact for 

 months, and resemble the natural shell indistinguishably. 



RELATION OF THE ABOVE EXPERIMENTS TO THE PHENOMENA 

 EXHIBITED BY LEUCOCYTES IN INFLAMMATION 



The experiments cited indicate strongly, to say the least, that 

 amebae, and presumably leucocytes, react to stimuli of various 

 kinds, chiefly through the effect of these stimuli upon surface 

 tension. The stimuli may come from within the cell, being in 

 this case the result of changes in composition brought about by 

 metabolic processes ; such chemical products alter the tension of 

 the surface nearest their point of origin, causing what appears 

 to be spontaneous motion. Stimuli acting from without may 

 be chemical, thermal, electrical, or mechanical, but in any event 

 they act as stimuli to motion through their effect upon surface 

 tension ; if they decrease the surface tension the cell goes toward 

 them ; if they increase the tension, the cell moves away. The 

 behavior of leucocytes in inflammation may be explained on 

 these purely physical grounds very satisfactorily, as follows : 



At the point of cell injury or of infection, substances are 

 produced that exert positive chemotaxis, as can be shown by 

 experiments both 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 chemo- 

 tactic effect is positive. As the chemotactic substances are 

 produced, they diffuse through the tissues until they reach the 

 walls of a capillary, through which they 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 substances most on the side from which the 

 substances diffuse ; the surface 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, 



