SPALDING, J.

The defendant was convicted upon a complaint charging that on December 21, 1965, he "did sell to a person under the age of eighteen years, a book entitled `Candy,' which was obscene, indecent, and impure, and manifestly tending to corrupt the morals of youth." The statute on which the complaint was based is G.L.c. 272, § 28 (as amended through St. 1959, c. 492, § 1), the relevant portions of which are: "Whoever sells . . . to a person under the age of eighteen years a book . . . which is obscene, indecent or impure, or manifestly tends to corrupt the morals of youth . . . shall be punished. . . ." The defendant appealed, the case having been tried subject to G.L.c. 278, §§ 33A-33G. The defendant's assignments of error arise out of exceptions to the denial of his motion for a not guilty finding, to the denial of three requests for rulings, and to the exclusion of expert testimony as to redeeming social value of the book. The requests asked the judge to rule: that the book was not obscene; that the portion of § 28 which proscribes the sale of a book "which manifestly tends to corrupt the morals of youth" violates the due process clause of the Fourteenth Amendment by reason of vagueness; and that the defendant could not be convicted without proof that he had knowledge of the contents of the book. We shall confine our discussion to the last issue (scienter), as in our view this is decisive of the case.

The facts are not in dispute. On December 21, 1965, a seventeen year old girl accompanied by another girl, aged fifteen, entered a Boston bookstore in which the defendant was an employee. The older girl asked to purchase a book entitled "Candy," which she had heard about, and which was displayed on a counter near the cash register. She paid the defendant for the book (a paperback) and he put it in a paper bag. After purchasing the book, the two girls left the store. When they got outside they were stopped by a police lieutenant who, after ascertaining their ages, took possession of the book and reimbursed them for the purchase price. Thereafter the officer brought the complaint on which this prosecution is based. The Commonwealth concedes that it introduced no evidence that the defendant had any knowledge of the contents or allegedly obscene character of the book.

The question for decision is very similar to that considered in Demetropolos v. Commonwealth, 342 Mass. 658. There it was held that G.L.c. 272, § 28A, which imposes criminal liability for the sale of obscene matter to the general public, although containing no express provision for scienter, must be construed as requiring scienter. The basis for that decision was that under Smith v. California, 361 U.S. 147, legislation which restricts the distribution of obscene matter without any requirement of knowledge on the part of the seller impinges upon the public's access to constitutionally protected matter. In the recent decision in Mishkin v. New York, 383 U.S. 502, 511, it was said, "The Constitution requires proof of scienter to avoid the hazard of self-censorship of constitutionally protected material and to compensate for the ambiguities inherent in the definition of obscenity." In People v. Finkelstein, 9 N.Y.2d 342, a statute proscribing the sale or possession for sale of obscene books was construed to require scienter, although the statute was susceptible of an interpretation excluding scienter. State v. Hudson County News Co. 35 N.J. 284, 289-294, is to the same effect. See State v. Sul, 146 Conn. 78; Cincinnati v. Marshall, 172 Ohio St. 280.

The Commonwealth contends that the Demetropolos and Smith decisions are not controlling because § 28, unlike the statutes involved in those decisions, is aimed only at sales to minors. The Commonwealth would liken § 28 to G.L.c. 138, § 34, imposing strict criminal liability on one who sells liquor to minors. See Commonwealth v. Gould, 158 Mass, 499, 507-508, and cases cited. While the "existence of a mens rea is the rule of, rather than the exception to, the principles of Anglo-American criminal jurisprudence," it is undoubtedly competent for the Legislature to define criminal offences without any element of scienter. See Commonwealth v. Mixer, 207 Mass. 141, 142-143, where numerous instances of strict criminal liability are collected. See also Smith v. California, 361 U.S. 147, 150.

But a different situation is presented when the legislation is in an area where First Amendment rights are involved. In Jacobellis v. Ohio, 378 U.S. 184, 195, there is a suggestion in the opinion of Mr. Justice Brennan that material protected for distribution to the general public is not necessarily constitutionally protected from restriction upon its dissemination to children. Two recent cases have discussed and applied this variable standard. Bookcase, Inc. v. Broderick, 18 N.Y.2d 71. Interstate Circuit Inc. v. Dallas, 366 F.2d 590, 594-597 (5th Cir.). See Am. Law Inst., Model Penal Code, § 251.4 (Proposed Official Draft, May 4, 1962); Lockhart and McClure, Censorship of Obscenity: The Developing Constitutional Standards, 45 Minn. L. Rev. 5, 68 et seq.; dissenting opinion of Cutter, J., in Attorney Gen. v. "John Cleland's Memoirs of a Woman of Pleasure," 349 Mass. 69, 76-78. Thus it may well be that the protective scope of the First Amendment is narrowed when the objectionable material is aimed primarily at minors. Yet, even under variable standards, the requirement of scienter of Smith v. California, supra, must still apply in construing § 28.

Absent the scienter requirement, booksellers, unable to familiarize themselves with all the material on their shelves, would tend to restrict sales to minors to the relatively few books of which they had some knowledge of the contents or character. The result would be an impediment to the sale to minors not only of unprotected matter but also of that which is constitutionally protected. To thus impede protected material is no more permissible under the variable than under the strict standard. See Lockhart and McClure, supra, at pages 103-114. "[W]here a statute may be construed as either constitutional or unconstitutional, a construction will be adopted which avoids an unconstitutional interpretation." Demetropolos v. Commonwealth, 342 Mass. 658, 660. We are of opinion that § 28 must be read as requiring scienter. Since proof of scienter was lacking, the judge erred in denying the defendant's motion for a not guilty finding.

Judgment reversed. Finding set aside.