Convex-lens-on-slide: a simple system for the study of human plasma and blood in narrow spaces

On clot-promoting surfaces, intact normal blood or plasma deposits fibrinogen and then supplants it with high molecular weight kininogen (HMWK). On glass, plasma layers of less than about 25 micron thick, while still containing enough fibrinogen to coat the surrounding surfaces, lack sufficient HMWK per surface area to remove this fibrinogen deposit. Thus normal intact citrated plasma allowed to enter the space between a glass slide and a convex lens resting belly-down on the slide will leave a disc of fibrinogen where the thickness of plasma layer was below this "critical height" H. The discs of fibrinogen left by plasma that lacks HMWK pathologically or by activation or dilution, are larger--the required H being greater. The present study shows that plasma dilution (final volume divided by original plasma volume) plotted against H yields a straight line. In preliminary series, the slope of this line increases with the atomic weight of five metals whose oxidized surfaces were used as substrates. In whole blood collected in either heparin or ACD, a circle of platelets adheres to oxidized silicon, anodized tantalum, or glass; this circle is similar in size to the one of fibrinogen left by plasma.