In this way the vocal cords may be seen in any stage of their vibrations, and the instrument may also be so adjusted that one series of vibrations is omitted, and the second step of the vibration is taken up, so that we apparently have a slow motion of the vocal cords, which enables us to study their action during voice production. This has given us much useful information, especially regarding the subject of the various registers of the human voice.
Having now explained the production of the voice under normal conditions, I must now show how this is affected by abnormal conditions, and also point out some suggestions as to the care of this important organ. You will remember that the vibrations of the vocal cords produce the fundamental elements of the voice. Any condition which prevents their free vibration will therefore interfere with the normal voice. The most frequent disturbances are due to 'colds' in which the vocal cords may become congested or inflamed. This produces a thickening of the vocal cords which lowers their rate of vibration, and, consequently, lowers the tone and gives rise to the hoarse voice characteristic of an ordinary cold. When this condition, from any cause, becomes chronic so that instead of a simple swelling of the vocal cords we have a chronic thickening, it may leave, unless corrected, a permanent defect in the voice.
A more serious influence on the voice is due to growths or tumors either on the vocal cords or 
Fig. 10. Small Tumor of Vocal cord interfering with voice production. in some other part of the throat, and interfering with the formation of vocal sounds. In the adjoining illustration, the small tumor shown between the vocal cords had caused hoarseness by interfering with the vibrations of the vocal cords, and by irritating the throat had set up a persistent cough. About eighteen months before being seen, the patient had leaped into the Mississippi River to save a child from drowning. The exposure was followed by a severe cold, leaving a persistent hoarseness, afterwards accompanied by a cough. About a year and a half afterwards, the patient was sent to me and a careful examination revealed this small tumor on the vocal cord, which affected his speech, so that it was of an extremely husky character. The following day this tumor was removed by means of an instrument passed from the mouth into the throat, the course of the operation being followed by means of a mirror as already explained, and being rendered painless by the application of cocaine, and the tumor removed. The voice being freed from the dampening
