1. Haemoglobin is by no means confined to the erythrocytes of higher animals, and is of extremely widespread occurrence in nature (Anson and Mirsky, 1925). For instance, it occurs in the rootnodules of leguminous plants containing rhizobium, and plays a part in nitrogen-fixation (Virtanen and Laine, 1946; Keilin and;Smith; Haemoglobin is also found dissolved in the blood of the crustacean genus Daphnia, particularly under conditions of low oxygen tension, and in the partho,1947
2. Adair, G. S. (1924). Proc. Camb. phil. Soc. biol. Sci., 1, 75.
3. Adair, G. S. (1925a). Proc. roy. Soc. A, 108, 627.
4. Adair, G. S. (1925b). Ibid., 109 292.
5. Allison, A. C. (1954). Brit. med. J., 1, 290.