§1. Subtraction of fictitious fields: Dirac's modified field-vectorpotential relation is discussed and elaborated in various directions, e.g., to include the case of a monopole wave-packet. §2. Field quantization: A way to incorporate monopoles into Tomonaga's quantum-electrodynamics is pointed out. §3. Comments on vacuum polarization: Contributions from virtual pole-anti-pole pairs are discussed with the use of duality aspects.