connective tissue it is possible to register their travel because they move forward through a retain- ing meshwork. It would not be possible to do so if they merely passed out into fluid, to be afterwards carried hither and thither by every chance con- vection current. Exactly the same applies to the extravascular blood. The emigrating leucocyte must be provided with some sort of scantling to move forward upon, and come to rest in.
After a time I alighted on a method which satisfies the two afore-mentioned experimental requirements, and which, as I think, provides all that is required for a quantitative estimation of emigration. Let me first tell you the general lines upon which the method proceeds, and then set out the details of the technique.
PRINCIPLE OF THE METHOD EMPLOYED FOR MAKING OBSERVATIONS ON EMIGRATION.
The principle of the method is as follows : We fill in a capillary tube with blood from a prick in the finger, immediately place the capillary tube in the centrifuge, and centrifugalise until we have carried down all the corpuscles. We have now in the upper half of the tube a plasma which has been completely freed from all formed elements ; and in the lower half of the tube, at the bottom, the red