Since a hydrogen ion (the atom minus its electron) is just a proton, we can as easily say that acids are substances that can contribute one or more protons to solution. Upon entering the mouth, those protons stimulate the flow of saliva, by which they are neutralized, and our taste buds tell us how much of this reaction is going on through the sensation of tartness. Acidity can thus be described as a flow of discharged protons sensed by the tongue.
