REGULATION OF RESPIRATORY MOVEMENTS 1217 



of inspiration or of expiration. The results of such an experiment 

 are shown in Fig. 508. 



A still more marked effect is produced if the lungs, by means 

 of a tube in the trachea, be artificially inflated or if air be sucked 

 out of them. The inflation produces an instantaneous and com- 

 plete relaxation of the diaphragm (Fig. 509) which by clamping 

 the tracheal tube may be prolonged for several seconds, while 

 sucking air out of the lungs causes a tonic contraction of the 

 diaphragm (Fig. 510). Somewhat similar results may be obtained 



Pos. ventilation 



Diaphragm 



[Seconds 



FIG. 509. Positive ventilation. (HEAD.) 



Under the influence of positive ventilation, the inspiratory contractions 

 of the diaphragm become less and less till they disappear completely. 



ventilation 

 Diaphragm 



FIG. 510. Negative ventilation. (HEAD.) 



At a negative ventilation was commenced. The expiratory relaxation of 

 the diaphragm is seen to become more and more incomplete, until it finally 

 enters into continued contraction. 



by repeatedly inflating or deflating the lungs (positive and nega- 

 tive ventilation). The effects here are complicated by the fact that 

 one is dealing in both cases with alternating movements of the 

 lungs, of expansion and contraction, both of which will have an influence 

 on the respiratory centre. Moreover repeated forcible inflation of 

 the lungs increases the ventilation of the pulmonary alveoli, thus 

 lowering the normal carbon dioxide tension of the lungs. As a result 

 of repeated ventilation we may obtain a condition of respiratory 

 standstill. In this condition, however, as we shall see later, the 

 determining factor is rather chemical than mechanical. 



These inhibitory and augmentor effects of changes in the 

 volume of the lung must also result from the normal movements of 



77 



