INNERVATION OF THE RESPIRATORY MOVEMENTS. 623 



labored breathing in which the expirations are active and forced. 

 When dyspnea is produced by withholding air (suffocation) the 

 respiratory movements become more and more violent until they 

 take on a convulsive character. This stage is succeeded by one 

 of apparent calm, indicative of exhaustion of the centers. Deep, 

 long-drawn inspirations follow at intervals and finally cease. The 

 animal lies quietly, with feeble heart beat and dilated pupils, in 

 a condition designated as asphyxia or complete asphyxia. 



The term apnea means literally a condition of no breathing, and 

 since this condition may occur from several causes some confusion in 

 nomenclature has resulted. In medical literature the term is some- 

 times employed as a synonym for asphyxia or suffocation. In 

 physiological literature it is restricted to a very interesting con- 



Fig. 251. To show the recovery from apnea. The animal (rabbit) had been venti- 

 lated with a bellows and thrown into a condition of apnea shown at the beginning 

 of the record. The respirations returned first as feeble movements which gradually in- 

 creased to the normal. (Dawson.) 



dition which is of great importance with reference to the theories 

 of respiration. This condition is one of cessation of breathing 

 movements due to lack of stimulation of the respiratory center. 

 It is brought about by rapid and prolonged ventilation of the 

 lungs. If, for instance, in a rabbit or other animal, a tracheal 

 cannula is inserted and connected with a bellows or respiration 

 apparatus, the lungs may be inflated artificially at a rapid rate 

 for any given period of time. If such an experiment is per- 

 formed it will be found that when the blasts are stopped the 

 animal makes no breathing movements at all, sometimes for a 

 considerable interval. When the respirations start again they begin 

 with feeble movements, which gradually increase to the normal 

 amplitude (Fig. 251). One may produce a similar condition upon 



