We succeeded in the extraction of a substance from beef cornea and rabbit muscle, that markedly inhibits mitosis of sea urchin eggs. The substance extracted from beef cornea is non-dialysable and it can be separated into three fractions by DEAE-cellulose column. Although everyone of these fractions has an antimitotic
action, that of fractions II and III is especially marked. These fractions are one of nucleoproteins that have adenine as base. The substance extracted from rabbit muscle is dialysable, and when it is fractionated through DEAE-cellulose column into three fractions, fraction I has no antimitotic effect but fractions II and III have it. Fraction II is one of nucleoproteins that have hypoxanthine
as base. Carnin obtained from beef cornea or from rabbit muscle shows a typical protein wave, but after being treated with gas by passing oxygen through cornin solution the wave height is lowered. Carnin, however, is a very
stable substance when kept dry in a desiccator.</p
