On the occasion of the hundredth anniversary of the term “synapse”, gradual progress of the knowledges conducting to the notion of chemical transmission was related. It was particularly stressed how the synapse was understood by the major contributors in this field. The soundness of the choice of the term synapse, instead of syndesm that was proposed at first, was underlined by a comparison of the original meanings of the two words and confirmed by their use in a treatise of Aristotle. It appeared that the notion of humoral immunity influenced the birth of humoral theory of chemical transmission, which was illustrated in the textbook of M. Verworn.