Fig. 2. Wheal size (mean values) at 15 min after intradermal injection of phenol physiologic diluent (ppd; negative control), histamine (histam; positive control), and five increasing log molar benzylisoquinoline neuromuscular blocking agent and succinylcholine concentrations on the forearm or the back in healthy volunteers. (  A ) Atracurium, (  B ) cisatracurium, (  C ) mivacurium, (  D ) succinylcholine.