The effect of some anticholinesterases on the response of the taenia to sympathetic nerve stimulation.

1. A preparation of the taenia from the caecum of the guinea-pig has been used. Acetylcholine caused contraction and noradrenaline caused relaxation. When the perivascular nerves running to the taenia were stimulated, at low frequencies there was sometimes contraction and sometimes relaxation. At high frequencies there was always relaxation. In the presence of hyoscine there was relaxation at all frequencies, the relaxation increasing as the frequency rose up to 20/sec. The relaxation was not affected by the presence of hexamethonium, but was blocked by bretylium.2. When stimulation was applied in the presence of hyoscine, the addition of physostigmine, Mipafox or Dyflos increased the relaxation to stimulation of low frequency, the increase becoming smaller as the frequency rose. At high frequencies Mipafox decreased the relaxation.