In the first part of this paper, the non-reiativistie theory of the interaction of mesotrons with heavy particles is developed. This theory is then applied to the absorption of a positive (negetive) mesotron by an atonnic nueeus with subsequent emission of a proton (neutron), and it is found that the cross-section par neutron (proton) in the nucleus is given by φ=45×10-28c/rcm2 (c"e)