In this paper the authors describe in detail compounds of dimethyl-thetine, some of which were enumerated in an earlier communication. Hydrobromate of dimethyl-thetine is readily obtained as a colourless crystalline body by the action of sulphide of methyl on bromacetic acid at ordinary temperatures. Its analysis shows that it contains quantities of the different elements agreeing with the formula C4H9BrSO2, and its mode of formation and reaction lead to the constitutional formula—