Malpighi's lung observations. 17th-century illustration of tissue from the lungs of a frog. These observations were published in 'De pulmonibus observationes anatomicae' (1661) by Italian biologist Marcello Malpighi (1628-1694). Although they were from a frog, Malpighi extended his findings to human lungs. He showed that the lungs had microscopic structure and he produced drawings of the pulmonary capillaries and alveoli. An alveolus is at top left, with a different view of an alveolus at centre left. At lower right is a diagram showing how the airways from the trachea branch into smaller airways, ending in the alveoli.