The most careful consideration which the Fourth Amendment has received by the Supreme Court is that contained in the opinion rendered in the case of Boyd v. United States.83

In this case the intimate relation between the Fourth Amendment and that clause of the Fifth which prohibits the accused from being compelled to be a witness against himself, is emphasized. "We have been unable to perceive," say the court, "that the seizure of a man's private books and papers to be used against him is substantially different from compelling him to be a witness against himself." "We are also of opinion," the court continue, "that proceedings instituted for the purpose of declaring the forfeiture of a man's property by means of offenses committed by him, though they may be civil in form, are in their nature criminal" and thus brought within the operation of the Fourth Amendment and that part of the Fifth which relates to self-incrimination.

82 96 U. S. 727: 24 L. ed. 877.

83 "The constitutional guaranty of the right of the people to be secure in their papers against unreasonable searches and seizures extends to their papers, thus closed against inspection, wherever they may be. Whilst in the mail, they can only be opened and examined under like warrant, issued upon similar oath or affirmation, particularly describing the thing to be seized. as is required when papers are subjected to search in one's own household. No law of Congress can place in the hands of officials connected with the postal service any authority to invade the secrecy of letters and such sealed packages in the mail; and all regulations adopted as to mail matter of this kind must be in subordination to the great principle embodied in the Fourth Amendment of the Constitution."

84 201 U. S. 43; 26 Sup. Ct. Rep. 370; 50 L. ed. 652.

85 116 U. S. 616; 6 Sup. Ct. Rep. 524; 29 L. ed. 746.

In this case the court held void the provisions of a customs revenue law of Congress of 1874, which authorized the courts, on motion of the govermnent, to require the defendant to produce his private books and papers, and in case of his refusal so to do, declared that the allegations of the government were to be held as confessed. This was held repugnant to both the Fourth and Fifth Amendments.86