  On a 3-dimensional contact manifold with boundary, a bypass attachment is an
elementary change of the contact structure consisting in the attachment of a
thickened half-disc with a prescribed contact structure along an arc on the
boundary. We give a model bypass attachment in which we describe the periodic
orbits of the Reeb vector field created by the bypass attachment in terms of
Reeb chords of the attachment arc. As an application, we compute the contact
homology of a product neighbourhood of a convex surface after a bypass
attachment, and the contact homology of some contact structures on solid tori.
