The various degrees of pitch in the compass of the voice depend upon the rate of vibration of the vocal cords. This rate of vibration, the pressure of breath being the same, is caused by the different degrees of tension of the vocal cords. If the vocal cords are drawn thin and short, the pitch will be high; as the tension diminishes, the pitch will be lower. The greater the number of vibrations to the second, the higher will be the pitch. A sound consisting of sixteen vibrations to the second produces the lowest pitch that has been recognized by the human ear as sound; while more than 38,000 vibrations per second have not been heard. The lowest rate of vibration on record of any voice is about forty-four vibrations per second, while the highest rate in any voice on record is a little over nineteen hundred. LOUDNESS. Different degrees of loudness of voice are caused by different degrees of amplitude of the waves of vibration. THE LUNGS. The two lungs are the essential organs of respiration; the right lung has three lobes, the left, two. The base of each lung rests upon the convex surface of the diaphragm. [Illustration: =FRONT VIEW OF THE HEART AND LUNGS, AND LARGE BLOOD-VESSELS.=] The root of each lung is formed by the bronchus and blood-vessels, which enter the lung a little above the middle of its inner surface, and connect it to the heart and trachea. With the exception of the root, the surface of each lung is free and moves in the cavity of the thorax. The bronchus is one of two tubes which arise from the bifurcation of the trachea. It conducts the air from the trachea to either lung. The bronchial tubes are sub-divisions, or ramifications, of the bronchus and terminate in the air-cells. _MUSCLES OF RESPIRATION._ Inasmuch as voice is vocalized breath, it is important to give attention to respiration. The principal muscles used in the ordinary movements of inspiration are:— I. Diaphragm. II. Levatores costarum. III. External intercostals. The principal muscles used in expiration are:— I. Internal intercostals with the infracostals. II. Triangularis sterni. { Transversalis. III. Abdominal muscles { Rectus. { Internal oblique. { External oblique. There are many accessory muscles which aid in violent respiratory movements, both inspiratory and expiratory. All the muscles which elevate the scapula may act through it upon the ribs; the three scalene muscles act directly upon the first rib. The principal muscles of inspiration may be assisted by the