A detailed but phenomenological analysis is made in estimating the contribution of the single-particle excitations to the integrated cross sections σpp' and σpn of the (p, p') and (p, n) reactions. It is found that, if the experimentally known collective-excitation cross section is added (which is in fact added only to the former), the resulting integrated cross sections agree very well with experiments and reasonably explain why σpp' ≫σpn. It should be noted, however, that the contribution of the collective excitation to σpp' turned out, in our analysis, to be only a small fraction of σpp', contrary to the supposition of Cohen that it is the main part of σpp'. To complement the above phenomenological analysis, somewhat more basic considerations of the mechanism of the direct interactions are made, using the T-matrix formalism. Discussions are given concerning the way how to describe the collective excitation in the inelastic scattering process as a superposition of single-particle excitations, in accordance with other authors, and also concerning the reason why the excitation of the collective states is expected to be small in the transmutation reactions.