376 
Proceedings of the Royal Society 
tube, as regards the .leucocytes, when the current becomes slow , 
while the coloured blood-corpuscles pass onwards without impedi- 
ment. When the stream is rendered more powerful the lighter 
spheres are also carried along. 
Another experiment was shown to illustrate how it is that in 
inflammation the leucocytes, after they have accumulated in the 
peripheral layer, are driven through the wall of the vessel. A tube 
was employed from which a portion, 6 inches long and for about half 
its circumference, had been cut out. This was covered with a mem- 
brane in which were several pinvpoint apertures. Pieces of a thin 
solution of gelatine, about half an inch square, were introduced into 
the tube. So long as the distal end of the tube is freely open, the 
water has only a slight tendency to exude from the apertures, and 
the pieces of gelatine have not any tendency to do so. When, 
however, the end of the tube is closed or partially obstructed, the 
membrane becomes distended. From the apertures in it little jets 
of water issue, and very soon the pieces of gelatine are attracted 
to the apertures, and are extruded from them in great numbers, 
though the pieces of gelatine are probably from thirty to sixty 
times as large as the apertures through which they make their exit. 
There is first noticed a little bud-like process outside the aperture ; 
this enlarges, and soon the whole mass is pushed through exactly 
like a leucocyte in an inflamed part. 
The conclusions from this experiment, and from other consider- 
ations are : — 
1. That the leucocytes in inflammation are driven through the 
natural apertures in the vessel wall by the diverted blood- 
pressure. 
2. That the reason of their being extruded in numbers greater 
than the coloured blood-corpuscles is that in the slowing of 
the blood stream, previous to their diapedesis, they have 
accumulated at the periphery, and are applied over the 
apertures in the vessel in preference to the coloured cor- 
puscles, wdiich are still circulating in its axis. If the circu- 
lation is suddenly arrested, as by ligature of a vein, the 
coloured corpuscles pass through the wall in much greater 
numbers than the colourless, the reason being that there has 
not been time to form a peripheral layer of leucocytes. 
