Jerrold Meinwald, who conducted pathbreaking studies of how creatures use chemicals to attract mates, repel predators and send other messages back and forth, died on April 23 at his home in Ithaca, N.Y. He was 91.

His death was reported by Cornell University, where Dr. Meinwald had worked for more than 50 years.

One project that Dr. Meinwald, an organic chemist, tackled soon after he arrived at Cornell in 1952 was determining what exactly in catnip drives some cats into a playful frenzy.

Dr. Meinwald isolated from the plant the active ingredient — a chemical called nepetalactone — and then deduced its structure.

He soon discovered an aspect of nepetalactone he had not known about. He was a giving a talk about his chemical findings, and someone had brought in a cat so he could demonstrate the effects.