Change and Exchange of Rest Mass of Elementary Particles During Collisions

In a recent letter I suggested [1] that the possiblity of a change of rest mass of elementary particles caused by collisions should be investigated. In general the distribution of energy and of momentum among the various particles which are involved in a collision will be complicated if a change of rest mass is taken into account. In two limiting cases, however, the results may be stated in a simple manner. These two cases are (A) an exhange of the rest masses between two elementary particles, and (B) a change of the rest mass of one individual particle which passes, for instance, through the field of a nucleus.