In Hawker v. New York (1898), 170 U.S. 189, 18 S.Ct. 573, 42 L.Ed. 1002, the Court struck down an ex post facto challenge to a New York statute that prohibited persons with felony convictions from practicing medicine. The Court determined that New York had good grounds for being concerned about the character of its physicians, stating: "That the form in which this legislation is cast suggests the idea of the imposition of an additional punishment for past offences is not conclusive. We must look at the substance and not the form, and the statute should be regarded as though it in terms declared that one who had violated the criminal laws of the State should be deemed of such bad character as to be unfit to practice medicine, and that the record of a trial and conviction should be conclusive evidence of such violation. All that is embraced in these propositions is condensed into the single clause of the statute, and it means that and nothing more. The State is not seeking to further punish a criminal, but only to protect its citizens from physicians of bad character." Id. at 196.