It is generally observed that there are various organ-specific mitotic rates in regeneration and compensatory growth. Nevertheless, each tissue can proliferate well in a suitable culture medium. These facts suggest that there are regulating substances for cell division. The author extracted an antimitotic substance "CORNIN" from rabbit and dog organs by the alcoholic fractionation, mainly from muscle layer and mucous layer of digestive organs. Each cornin of internal organs has less antimitotic effeet on sea urchin eggs than that of muscle or cornea. Furthermore, there are no difference between muscle layer and mucous layer as regards the antimitotic effect. There is no difference in the qualitative analysis of cornins for protein and sugar. Typical protein waves are shown by polarogram excepting cornin of regenerating rat liver. The ultra-violet absorption curves show the same maximum absorption peak at 260 mμ, which is the same as that of corneal cornin, but is different from muscle cornin that shows the peak at 249 mμ. The paper electrophoresis does not show any remarkable fifferences among these cornins.
With respect to the cornin activity, there can be seen no remarkable difference between muscle layer and mucous layer.