Abstract
Methods for counting platelets are either direct or indirect. As noted in the preceding paper we have used both. In our hands an indirect method, based on that described by Cramer, Drew and Mottram 1 using the diluting fluid recommended by Rees and Ecker 2 has yielded the most reliable results. The fluid is 3.8 per cent sodium citrate, to which 0.2 percent formaldehyde and 0.1 percent brilliant cresyl blue are added. It is filtered clear every three days. The same pipettes and counting chambers have been used throughout.
The tip of the tail is shaved, then scrubbed clean and coated with vaseline. With vaselined scissors about 1 cm. of the tail is clipped off, the skin on the stump pushed forward and the bared tip quickly immersed in the solution and a single drop of blood allowed to flow into the fluid. Immediately thereafter, with the red pipette, filled to the 0.5 mark, blood is sucked up from the tail stump to the 1.0 mark and then again with diluting fluid to the 1.01 mark. This gives the sample for the direct red and platelet count.
The solution containing the first drop of blood is mixed thoroughly for a few moments, a drop withdrawn, placed upon a thoroughly cleaned slide, covered with a clean cover glass and sealed with paraffin. After standing, in order that the reds and platelets may settle out, a proportional count is made. Usually three hundred red cells are counted.
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