His letters show that Harvey was employed almost to the end of his life in devising fresh experiments in proof of the circulation of the blood. Thus, in a letter addressed to Paul Marquard Slegel, and dated London, this 26th of March, 1651, Harvey writes: "It may be well here to relate an experiment which I lately tried in the presence of several of my colleagues.... Having tied the pulmonary artery, the pulmonary veins, and the aorta, in the body of a man who had been hanged, and then opened the left ventricle of the heart, we passed a tube through the vena cava into the right ventricle of the heart, and having at the same time attached an ox's bladder to the tube, in the same way as a clyster-bag is usually made, we filled it nearly full of warm water and forcibly injected the fluid into the heart, so that the greater part of a pound of water was thrown into the right auricle and ventricle. The result was that the right ventricle and auricle were enormously distended, but not a drop of water or of blood made its escape through the orifice in the left ventricle. The ligatures having been undone, the same tube was passed into the pulmonary artery and a tight ligature having been put round it to prevent any reflux into the right ventricle, the water in the bladder was now pushed towards the lungs, upon which a torrent of the fluid, mixed with a quantity of blood, immediately gushed forth from the perforation in the left ventricle: so that a quantity of water, equal to that which was pressed from the bladder into the lungs at each effort, instantly escaped by the perforation mentioned. You may try this experiment as often as you please: the result you will still find to be as I have stated it." The exact teaching of Harvey's contemporaries in London is easily accessible. One of his distinguished colleagues at the College of Physicians was Alexander Reid, son of the first minister of Banchory, near Aberdeen, brother of Thomas Reid, Secretary for Latin and Greek to King James I. Reid was born about 1586, learnt Surgery in France, was admitted a Fellow of the College of Physicians in 1624, and was appointed Lecturer on Anatomy at the Barber Surgeons' Hall December 28, 1628, in succession to Dr. Andrewes, Harvey's assistant. Reid, eight years younger than Harvey, lectured at an annual stipend of £20 on every Tuesday throughout the year from 1628 to 1634, when he published a tiny Manual of Anatomy containing the substance of his lectures. For some reason Harvey's doctrines did not recommend themselves to Reid, and the Manual therefore contains the following traditional account of the heart.