It is judicially settled that “The details with which the exemptions in this Act have been made preclude their enlargement by implication” and “no matter how broad the exemption, it is meant to apply only to” the employment specified in the statute. Conditions specified in the language of the Act are “explicit prerequisities to exemption.” Accordingly, it is the well-established rule that exemptions from the Act “are to be narrowly construed against the employer seeking to assert them” and their applications is limited to those who come “plainly and unmistakably within their terms and spirit.” An employer who claims such an exemption has the burden of showing that it applies. See Wirtz v. Lunsford, 404 F. 2d 693 (C.A. 6); Addison v. Holly Hill, 322 U.S. 607; Maneja v. Waialua, 349 U.S. 254; Phillips v. Walling, 334 U.S. 490; Arnold v. Kanowsky, 361 U.S. 388; Mitchell v. Kentucky Finance Co., 359 U.S. 290; Walling v. General Industries Co., 330 U.S. 545.