In the heart, lungs, large arteries and veins, About one-fourth. In the liver,  ,,      ,,      In the skeletal muscles,  ,,      ,,      In the other organs,  ,,      ,,      The average proportion of the principal constituents of the blood in 1,000 parts is: Water, 784 Red corpuscles (solid residue), 130 Albumen serum, 70 Saline matter, 6.03 Extractive fatty matter, 7.77 Fibrine, 2.20 The chemical composition of hæmoglobin is: Carb. Hyd. Iron. Nit. Oxy. Sulph. 54.2 7.2 0.42 16.0 21.5 6.7 Mucine, 52.2 7.0 12.6 28.2 Proteids, 51.5 6.9 15.2 20.9 0. to 54.5 to 7.3 to 17.0 to 23.5 to 2.0 THE ORGANS OF RESPIRATION. The principal organs of respiration consist of larynx, trachea, bronchi, lungs. The larynx is affixed to the upper end of the windpipe, and is not only the entrance for air into the respiratory organs from the pharynx, but also the organ of voice. The trachea measures from four inches to four inches and a half in length, and from three-quarters of an inch to one inch in width; but its length and width are liable to continual variations, according to the position of the larynx and the direction of the neck. The trachea divides into two branches, called bronchi, right and left. The right bronchus, wider and shorter than the left, measuring about an inch in length, passes outwards almost horizontally into the root of the right lung on a level with the fourth dorsal vertebra. The left bronchus, smaller in diameter but longer than the right, being nearly two inches in length, inclines downwards and outwards to reach the root of the right lung, which it enters on a level with the fifth dorsal vertebra--that is, about an inch lower than the right bronchus. The lungs, placed one on the right and the other on the left of the heart and large vessels, occupy by far the larger part of the cavity of the chest, and during life are always in accurate contact with the internal surface of its walls. Each lung is attached at a comparatively small part of its flattened inner or median surface by a part named the root and by a thin membranous fold, which is continued downwards from it. The pleuræ are serous membranes forming two shut sacs, quite distinct from each other, which line the right and left side of the thorax, forming by their approximation in the middle line the mediastinal partition, and are reflected each upon the root and over the entire free surface of the corresponding lung.