Proton Structure reexamines the original deep inelastic scattering data generated by the Stanford Linear Accelerator Center (SLAC) in the late 1960s and early 1970s. It shows that the proton and the deuteron structure functions appear to peak at a proton momentum fraction of 1/9. This indicates that the proton (and the neutron) is made of nine particles. Based on their masses and charges, it proposes that those particles are four muons and five antimuons...