It's being studied through the technics of Koelle-Friedenwall for the detection of specific acetyl-cholinesterase, that of Champy-Maillet of tetroxide osmium-iodine of zinc and that of Jabonero's silver carbonate, the microganglions existing in pulmonary vessels. The attained results with Koelle-Friedenwall's technics were negative. With the other two technics we have observed small microganglions attached to the adventitial layer of pulmonary vessels, as much arteries and veins. In one case, we have realised the existence of a neuronal conglomerate inside the adventitial itself. They are formed by a scarce number of neurons, type I from Dogiel. We believe, due to its localization, that they are of a parasympathetic nature.