Difference between mouth organ and harmonica?

The Harmonica is the brand name for the instrument the Mouth Organ. The Mouth Organ is a Reed Organ played using the mouth and lungs to supply the positive and negative air flow that other reed organs use bellows for. The American reed organ plays using negative air pressure ie it sucks and the Harmonium blows. The Mouth organ is the only wind instrument to use positive & negative air flow to voice reeds sounding different pitches on the suck and blow.