Abstract
In 1890, Müller described, from the lung of the cat, a species of nematode which is now known as Aelurostrongylus abstrusus. In 1928, I was able to show that its true habitat was not the lung substance, but the pulmonary artery and its branches, and that its pathogenic action, was mainly, if not entirely, due to the presence of the developing eggs and larvae distributed throughout the lung tissue by the blood stream.