While the theory of stereo-isomerism has been employed in the case of many carbon compounds, it has had but few applications in that of organic substances containing nitrogen. Its use has been almost confined to explaining the occurrence of isomers among the oximes. The addition of a new member to the small list of four or five pairs of hydrazones, whose isomerism can be explained only on the assumption of diversity in the disposition of the atoms in space, is therefore not unwelcome as giving additional weight to the theory.