For, since the process of stimulation is, to a certain degree, unspecific and furthermore interference in stimulus frequencies which certainly form the basis of some inhibitory manifestations in the animal region of the central nervous system cannot, in the case of peripherally inhibitable organs, be regarded as the cause of inhibition, I see no other possibility, at least in general, as to how nerve stimulation can lead to inhibitions of the effector organ at all than by chemical means; in other words, the chemical mechanism is the only conceivable way.    From Wordnik.com.  [Otto Loewi - Nobel Lecture] Reference