188 CAPILLARY CIRCULATION. 



its original form. This is a good proof of the elasticity of the 

 coloured corpuscles. 



Colourless Corpuscles. The motion of the colourless corpuscles is 

 quite different in character; they roll directly on the vascular icall, 

 moistened on their peripheral zone by the plasma in Poiseuille's space, 

 their other surface being in contact with the thread of coloured cor- 

 puscles in the centre of the stream. Schklarewsky has shown by 

 physical experiments, that the particles of least specific gravity in all 

 capillaries (e.g., of glass) are pressed toward the wall, while those of 

 greater specific gravity remain in the middle of the stream. [Graphite 

 and particles of carmine were suspended in water, and caused to 

 circulate through capillary tubes placed under a microscope, when the 

 graphite kept the centre of the stream, and the carmine moved in the 

 layer next the wall of the tube.] 



When the colourless corpuscles reach the wall of the vessel, they 

 must roll along, partly on account of their surface being sticky, whereby 

 they readily adhere to the vessel, and partly because one surface is 

 directed towards the axis of the vessel where the movement is most 

 rapid, and where they receive impulses directly from the rapidly 

 moving coloured blood-corpuscles (Donders). The rolling motion is 

 not always uniform, not unfrequently it is retrograde in direction, 

 which seems to be due to an irregular adhesion to the vascular 

 wall. Their slower movement (10 to 12 times slower than the 

 red corpuscles) is partly due to their stickiness, and partly to the 

 fact that as they are placed near the wall, a large part of their 

 surface lies in the peripheral threads of the fluid, which of course 

 move more slowly (in fact the layer of fluid next the wall is passive 

 p. 117). 



[D. J. Hamilton finds that, when a frog's web is examined in a 

 vertical position, by far the greater proportion of leucocytes float on 

 the upper surface, and only a few on the loAver surface, of a small blood- 

 vessel. In experiments to determine why the coloured corpuscles 

 float or glide exclusively in the axial stream, while a great many, but not 

 all, of the leucocytes roll in the peripheral layers, Hamilton ascertained 

 that the nearer the suspended body approaches to the specific gravity 

 of the liquid in which it is immersed, the more it tends to occupy the 

 centre of the stream. He is of opinion that the phenomenon of the 

 separation of the blood-corpuscles in the circulating fluid is due to the 

 colourless corpuscles being specifically lighter, and the coloured either 

 of the same or of very slightly greater specific gravity than the blood- 

 plasma. Hamilton controverts the statement of Schklarewsky, and he 

 finds that it is the relative specific gravity of a body which ultimately 

 determines its position in a tube. These experiments point to the 



