B. In the limbs: 3. Muscles of the upper extremities, 58 4. Muscles of the lower extremities, 59 Flesh and blood have nearly the same ultimate composition. On evaporating 1000 parts of blood it yields 790 parts of water and 210 parts solid residue. The elements that enter into the composition of the solid matter are as follows: Flesh. Blood. Carbon, 51.86 51.96 Hydrogen, 7.58 7.25 Nitrogen, 15.03 15.07 Oxygen, 21.30 21.30 Ashes, 4.23 4.43 The general composition of a human muscle is shown by the following table: Water, 744.5 { Myosin and other matters, { elastic elements, etc. 155.4 Solids. { Soluble elements, 19.3 { Gelatine, 20.7 { Extractives, 37.1 { Fats, 23.02 55.5 The muscles of the flesh form a large proportion of the weight of the whole body. Calculated for a man of 150 pounds' weight: The skeleton, bone, 27 lbs. The muscles, 63  ,,  The viscera, with skin, fat, blood, etc., 60  ,,  The property of muscular tissue by which its peculiar functions are exercised, is its contractility--contraction or shortening. This is excited by all kinds of stimuli, applied either directly to the muscles, or indirectly to them through the medium of their nerves. The muscular tissues perform all the physical work--as locomotion, every kind of action and exertion--of the body. The quantity of blood circulated through the body is estimated to be from about 1/10 to about 1/13 part of the body's weight, and about 1/4 of that is distributed in the muscles. As regards the action of the muscles the following general principles ought to be kept in view: 1. That the force exerted by any muscle during its contraction is in proportion to the number of muscular elements or fibers composing the muscle. 2. That the extent of motion, in so far as it merely depends on the shortening of the fibers of the muscle, is in proportion to the length of the fibers. 3. That the direction of the force produced by a contracting muscle is in the line of the axis of the whole muscle if it runs straight between its opposite points of attachment, but in the line of the portion attached to the moving part of the muscle, or its tendon, if it be bent in its course, etc. THE CEREBRO-SPINAL SYSTEM. The Nervous Tissue. The nervous system consists of the cerebrum, pons varolii, cerebellum, medulla oblongata, the spinal cord with its nerves and the sympathetic ganglia, etc.