I. Undor Calculus and Charge-Conjugation.- Zusammenfassung. Resumo.- § 1. Introduction.- § 2. The Dirac wave-function (undor of the first rank).- § 3. Charge-conjugation of four-spinors.- § 4. Neutrettors of the first rank.- § 5. Undors of the second rank.- § 6. Covariant undor calculus.- References.- II. The Undor Equation of the Meson Field.- Zusammenfassung. Resumo.- § 1. The Proca-Kemmer meson equation in undor notation.- § 2. The generalized meson equation and the neutretto equation.- § 3. The charge-conjugated meson equation.- § 4. The charge current-density and the magnetic moment of mesons.- § 5. Charge-invariance and statistics.- References.- III. The Heavy Quanta Theory of Nuclear and Cosmic Ray Phenomena.- § 1. Introduction.- § 2. The four types of meson fields proposed by Kemmer and the simplified deuteron problem.- § 3. The charge-dependence of nuclear forces.- § 4. Quantization and relativistic invariance of the theory.- § 5. Elimination of the longitudinal electromagnetic field.- § 6. Discussion of the Hamiltonian.- § 7. The heavy quanta interaction between nuclons.- § 8. The deuteron problem.- § 9. The neutron-proton scattering.- § 10. The spontaneous disintegration of heavy quanta..- § 11. The ?-disintegration of instable nuclei.- § 12. Scattering and absorption of mesons by nuclei.- § 13. Discussion of the limits and the value of the theory.- References.- Samenvatting.