“…Pick and Zukerkandl (1935) also investigated this technique. Other fluors, including acriflavine, primulin, rhodamine B, and thioflavin S, were employed by Keller (1949) with submerged animal tissues. Keller and Pisha (1947) stained living plants and animals with rhodamine B after fluorescein thus permitting the appearance of two fluorescent colors in their preparations.…”