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Text-books on clinical diagnosis usually give two diluting fluids for making the erythrocyte count in blood-work. These are Toisson's and Hayem's solutions. Toisson's fluid is difficult to prepare, as weighing the stipulated 25 mg. of methyl violet requires great care to secure the necessary accuracy, and more delicate scales than the average laboratory possesses. Then it is not always permanent, as molds may grow in it, forming precipitates. Hayem's solution has no added coloring-matter, and so the cells are not brought into clear relief. With this fluid it is also difficult to differentiate the white and red cells. I have for some time been using a diluting-fluid that is easily prepared, keeps permanently, and has all the advantages of either Toisson's or Hayem's solutions. The formula follows:
The various ingredients are added to the distilled water and allowed to stand until solution occurs. After being filtered, the preparation is ready
Callison JG. EASILY PREPARED DILUTING FLUID FOR COUNTING RED CELLS. JAMA. 1914;LXII(14):1086. doi:10.1001/jama.1914.02560390026014