VOICE AND SPEECH. 389 



ventilation. It appears, however, from experiments that when the 

 lungs have been distended with air, there is besides the distention 

 enough oxygen in the alveoli to aerate the blood for a time, so that 

 it is probable that physiologic apnea is produced by positive 

 ventilation, distention, and the excess of oxygen in the alveoli. 

 Apnea is also used as a synonym for asphyxia ; in this case the 

 qualifying adjective " physiologic J ' is omitted. 



Dyspnea. This is difficult or labored breathing. If caused 

 by a deficiency of oxygen, it is 0-dyspnea; if by an excess of 

 carbon dioxid, C0 2 -dyspnea. 



Hyperpnea. In this form of breathing the rate is moderately 

 accelerated. 



Asphyxia. The term literally means pulselessness, and is espe- 

 cially applicable to the last stage. 



If by any means the supply of air to an animal is cut off, or 

 so diminished in amount as to be exhausted, the animal dies in a 

 short time from asphyxia, passing previous to the fatal termination 

 through the following stages : 



(1) Hyperpnea. This stage is characterized by an increased 

 frequency of the respiratory movements, especially marked during 

 inspiration, because of the increased stimulation of the inspiratory 

 center. 



(2) Dyspnea. In this stage, the expiratory center is espe- 

 cially stimulated, and as a result the movements of expiration 

 are more pronounced than those of inspiration, the expiratory 

 muscles (p. 371) being brought into action. These two stages last 

 about one minute. 



(3) Convulsion. This stage is characterized by convulsive 

 movements throughout the body. 



(4) Exhaustion. The expiratory muscles being exhausted, the 

 animal becomes quiescent, only a few slight attempts at inspiration 

 being perceptible. After a time these become deeper, but only 

 occur at comparatively long intervals. 



(5) Inspiratory Spasm. The intervals between the inspirations 

 have in this stage greatly increased, and apparently ceased, but 

 they recur occasionally. The pupils are dilated and the pulse 

 becomes less and less perceptible ; finally a last inspiration occurs 

 and the animal is dead. 



VOICE AND SPEECH. 



The voice is produced by the vibration of the true vocal cords, 

 vocal bands, or vocal ligaments, by all of which terms they are 

 called, these being set in vibration by the respired air as it passes 

 out from the lungs, if at the time the bands are approximated and 

 tense, and if, also, the current of air is sufficiently strong. At the 

 same time, the sounds produced by the vibrating bands are sup- 



