Gebruiksaanwijzing bij Pro-kit (Individual Chemical Prophylactic Packet, for protection against venereal disease), G. Barr & Co. Chicago U.S.A., 1925-1950
o.a.: Pro Kit / U.S. Pat. Off. Reg. App. For / Individual Chemical Prophylactic Packet (for protection against venereal disease only) [...] G. Bar & Co. Chicago, Ill, U.S.A.