From late on October 29 until November 3, 1972, our experiment on the European Space Research Organization satellite Heos 2 recorded the arrival of an enhanced interplanetary particle intensity. A dramatic 'slot' in count rate and other sudden anisotropy and flux changes (measured in and perpendicular to the ecliptic plane) were found to coincide with changes in the ϑ (north-south) ecliptic direction of the interplanetary magnetic field. However, reorientation of strongly field-aligned particle distributions relative to the detectors was insufficient to explain the intensity changes recorded, and the conclusion had to be drawn that the spacecraft was repeatedly crossing a boundary between one regime and a neighboring one with a different particle population. Since the switching from one regime to the other continued for several days, it would seem reasonable to suggest that the boundary between regimes was roughly parallel to the ecliptic plane. This idea was reinforced by the discovery that each time that the particle regime changed, not only did Bϑ change, but the solar wind flow direction changed, the dip angle reversing sign. It would thus appear that when the solar wind blows three-dimensional snakelike tubes in interplanetary space, MeV particles obediently follow the field line bundles within such tubes and experience considerable difficulty in crossing from one tube to a neighboring tube which encloses a different regime. Because of the absence of cross-field particle movement, measurements made at higher solar latitudes, where most solar active regions occur, could reveal a somewhat different picture of the development of solar particle events.