  The detailed consideration of the relativistic canonical quantum-mechanical
model of an arbitrary spin-multiplet is given. The group-theoretical analysis
of the algebra of experimentally observables physical quantities for the spin
1/2 doublet is presented. It is shown that both the Foldy-Wouthuysen equation
for the fermionic spin 1/2 doublet and the Dirac equation in its local
representation are the consequences of the relativistic canonical quantum
mechanics of the corresponding doublet. The mathematically well-defined
consideration on the level of modern axiomatic approaches to the field theory
is provided. The hypothesis of the antiparticle negative mass is discussed
briefly in the section conclusions.
