The essentials of a good method for platelet counting are: (1) an efficient anticoagulant; (2) absence of contact between the undiluted blood and any instrument; (3) preservation and fixation of red blood corpuscles; (4) low specific gravity of diluting solution, and (5) a dye that will readily stain the platelets. To these five might be added a sixth, in case the method is for clinical use; namely, that the solution must be reasonably easy to prepare, and must be stable. The solutions recommended by Pratt,1 Wright and Kinnicutt,2 Buckman and Hallisey,3 Bizzozero4 (osmic acid anticoagulant, found unsatisfactory by Kemp, Calhoun and Harris5) were all found to present features that made satisfactory counts doubtful.
After experimenting with the anticoagulants of the foregoing methods, we reached the conclusion that sodium citrate is by far the most efficient in preventing clumping of the platelets.
The use of the