  Atmospheric neutrinos arise from the decay of particles (primarily pions,
muons and kaons) produced in the collision of high energy cosmic ray particles
with the atmosphere. The great distances traveled by atmospheric neutrinos
between their production and detection make them useful for studying neutrino
oscillations, the predicted phenomenon of massive neutrinos changing flavor in
flight. This thesis reports a study of atmospheric neutrinos interacting in the
MACRO detector. The results, though somewhat clouded by large theoretical
uncertainties, clearly rule out the no-oscillations hypothesis, and are
consistent with oscillations with the parameters preferred by other MACRO
neutrino analyses, as well as those of other experiments (most notably
Super-Kamiokande). Combining this analysis with another MACRO neutrino
analysis, some of the theoretical errors cancel, further constraining the
region of allowed oscillation parameters.
