492 MANUAL OF PHYSIOLOGY. 



with age, particularly in males, whose vocal organs undergo rapid 

 growth at puberty, when the voice is said to crack. The vocal 

 cords of women have been found by measurement to be about 

 one-third shorter than those of men, and people with tenor voices 

 have shorter cords than basses or baritones. Secondly, on the 

 tension of the cords : the tighter the vocal cords are drawn by 

 the crico-thyroid muscles, the higher the notes produced ; and 

 the well-known singer Garcia believed he observed with the 

 laryngoscope the vocal processes so tightly pressed together as 

 to impede the vibration of the posterior part of the cords, and 

 by this means they could be voluntarily shortened. 



(3.) Intensity or loudness of the voice depends solely on the 

 strength of the current of air. The more powerful the air blast, 

 the greater amplitude of the vibrations, and hence the greater 

 the sound produced. The narrower the chink of the glottis, and 

 the tighter the parallel cords are stretched, the less is the amount 

 of air and the weaker is the blast required to set them vibrating; 

 and vice versd, the looser the cords and the wider apart they are, 

 the greater the volume and the force of the air current necessary 

 for their complete vibration. Hence it is that an intense vibra- 

 tion or loud note can be produced much more easily with notes 

 of a high pitch than with very low notes, and we find singers 

 choosing for their telling crescendo some note high up in the 

 range of their voice. 



The human voice, including all kinds of voice, extends over 

 about three and a half octaves. Of this wide range, a single 

 individual can seldom sing more than two octaves. The soprano, 

 alto, tenor and bass form a descending series, the range of each 

 one of which considerably overlaps the next in the scale. 



During the ordinary vocal sounds, the air, both in the reso- 

 nating tubes above the larynx and in the windpipes coming from 

 below, is set vibrating, so that the trachea and bronchi act as 

 resonators as well as the pharynx, mouth, etc. This may be 

 recognized by placing the hand on the thorax, when a distinct 

 vibration is communicated from the chest wall. Such tones are, 

 therefore, spoken of as chest notes. Besides the chest tones of 

 the ordinary voice, we can produce notes of a higher pitch and 



