In view of the number of cases of epidermal cancer, especially cancer of the scrotum, which have occurred amongst cotton mule spinners within recent years, constituting this the foremost occupational cancer in our country, it may be opportune to investigate the exact duration of employment in the mule rooms that would seem to be necessary before the disease manifests itself. How long must the individuals be exposed to the action of the cancerinducing influence before the cancerous response is elicited? The Departmental Committee on Mule Spinners' Cancer having found that the “influence” or agent in this case is mineral oil, which Leitch has proved experimentally to have cancer-producing properties, how long does it take to act?