+ 
1878.] Microscopy. 765 
cytes in passive hyperæmia, frogs were curarized, the femoral vein 
exposed by dissection, and pressure applied by meäns of an India 
rubber band and a plug of cork. ‘Lhe web of the corresponding 
foot was stretched upon the stage of hie microscope, and the 
pressure upon the vein regulated so as to retard the current of 
blood without producing complete stagnation. That the effects 
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sparsely supplied with corpuscles, as well as from slow cur- 
rents crowded with corpuscles. The time of exit averaged 
from one to two hours, but was sometimes as short as twenty 
minutes. The method of locomotion did not, of course, differ 
from that exhibited in inflammation, though excessive change of ` 
form, and protrusion of long processes, was not noticed. Fre- 
a 
motion was continued after the leucocyte had wholly left the 
vessel, so that it traveled several times its own diameter from the 
place of exit. Other corpuscles, too, were prone to pass out at 
the same point, so that sometimes several would be crowded to- 
gether within the vascular wall, and an hour later would be in 
close proximity external to the vessel opposite the same point. 
Certain red corpuscles of the same shape and size, and without a 
nucleus, but of unmistakably red color, were frequently seen to mi- 
grate in a similar manner, and to such an extent that after thirty- 
six hours there were many patches in the field which looked 
almost like hemorrhages. That they were not hemorrhages was 
inferred, because many of them had been seen to migrate, because 
they were fixed in the tissue, and not floating in the blood serum, 
and because they were all small and round, and different from the 
large, oval, nucleated red corpuscles of the animal experimented 
upon. This behavior of the small red corpuscles exhibits a close 
relation with the white, and furnishes another link in the chain of 
at the migration is a simple filtration of colloid substances, from 
increased blood pressure and diminished blood velocity, rather — 
