 Around 300 BC, Praxagoras discovered the distinction between the arteries and the veins, although close studies of vascular anatomy had been ongoing since at least Diogenes of Apollonia.In the corpse arteries are empty; hence, in the light of these preconceptions they were declared to be vessels for conveying "pneuma" to the different parts of the body.A generation afterwards, Erasistratus made this the basis of a new theory of diseases and their treatment.