Portrait of the English physiologist Richard Lower, 1631-1691. Lower qualified in medicine at Oxford and moved to London to practise. He was an early member of the Royal Society. In 1665 he demonstrated the transfusion of blood from the artery of one dog to the vein of another. Later attempts by others to transfuse from animals to humans led to some deaths. Lower's Treatise on the Heart describes the heart as muscular pump rather than an organ 'inflated by spirits'. He deduced that the bright red of arterial blood results from the mixing of dark venous blood with inspired air in the lungs. From the 1670s on, he concentrated on his medical practice.