And, first, I find every part of the surface of his body possessing a nearly uniform temperature, which is higher than that of the surrounding atmosphere. There is, moreover, on all parts of the body, a tinge of redness, more or less vivid in certain regions. The heat, and the carnation tinge, alike indicate the presence of blood, arterial blood, diffused throughout, and, in particular, occupying the capillaries of the superficial parts. Every drop of this blood is preceded and succeeded by other drops, every one of which has been impelled out of the heart by its constant contractions. But the very existence of this blood supposes the pre-existence of chyle and lymph, out of which it has been constructed. The chyle was formed out of chyme, changed by the action of the pancreatic and biliary secretions. Chyme is food, chemically altered by the action of the gastric juice. So that the blood, now coursing through the arteries and veins, implies the previous process of the reception of food. And these pancreatic and biliary secretions, which are essential to the conversion of chyme into chyle,--and therefore into blood,--do you ask their origin? They were prepared, the one by the pancreas, the other by the liver, from blood already existing,--blood _previously formed_ of chyle with the addition of bile, &c.--and so indefinitely. Again, the blood in these capillary arteries is of a bright scarlet hue, which it derives from its being charged with oxygen. This it received in the _lungs_, parting at the same time with the carbon which it had taken up in its former course. The lungs then must have existed _before_ the blood could be where and what it is, viz. arterial blood in the capillaries of the extremities; before it was driven out of the heart, since it was transmitted from the lungs through the pulmonary veins into the heart, thence to be pumped into the arterial system. But since all the tissues of the body are formed from the blood, the lungs were dependent on already-existing blood for their existence. And as the formative and nutrient power is lodged exclusively in _arterial_ blood, the very blood out of which the lungs were organized was dependent on lungs for oxygenation, without which it would have been effete and useless. Here then is a cycle of which I cannot trace the beginning.