1942, 56 Stat. 1035, 42 U.S.C.Supp. II, § 1651(a)(3), 42 U.S.C.A. § 1651(a)(3), providing that the provisions of the Act shall not apply to employees of a 'subcontractor who is engaged exclusively in furnishing materials or supplies.' In other statutes, Congress has clearly used the term 'subcontractor' in contrast to 'materialman.' See 40 U.S.C. § 407(b), 40 U.S.C.A. § 407(b); 41 U.S.C. § 10b(a) and (b), 41 U.S.C.A. § 10b(a, b); 41 U.S.C. § 28, 41 U.S.C.A. § 28.