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Alexandre-Léon Étard (1852-1919) was a French chemist who studied alkaloids in general and nicotine in particular. Together with Cahours he investigated the reaction of nicotine with sulfur, synthesized tetrapyridine and studied its reaction with a variety of reagents. The results indicated that nicotine could be considered a combination of bipyridine and hydrogen, which upon reaction with sulfur transformed into tetrapyridine and thiotetrapyridine. The latter reacted with nitric acid yielding isobipyridine. The reaction with selenium and other reagents led to the formation of hydrocollidine and isopyridin, and the proposal of the possible formula of pyridine. Étard also studied the phenomenon of putrefaction and hydrolysis of tissues. He found that the release of nitrogen signaled the beginning of putrefaction, accompanied by the replacement of large bacilli by smaller ones. In the absence of air, putrefaction split the albumen molecule and proceeded by simple hydration. He studied in detail the substances that accompanied the chlorophyll present in vegetables and concluded that the green matter present in leaves contained a fundamental nucleus, very stable, that carried the function of optical absorption connected to the biological work. To this nucleus different chemical groups could be attached, giving place to chlorophylls that differed in their composition, molecular mass, isomerism etc. and the role they played in living plants. Étard and Vila separated a benzoyl derivative from the products of the hydrolysis of tissues and claimed that it was the cause of the many accidents that occurred during the eating of muscles. [ABSTRACT FROM AUTHOR]