REGULATION OF THE RESPIRATORY MOVEMENTS 1141 



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 complete relaxation of the dia- 

 phragm (Fig. 524) which by clamping the tracheal tube may be prolonged 

 for several seconds, while sucking air out of the lungs causes a tonic contrac- 

 tion of the diaphragm (Fig. 525). Somewhat similar results may be obtained 

 by repeatedly inflating or deflating the lungs (positive and negative ventila- 

 tion). The effects here are complicated by the fact that one is dealing in 

 both cases with alternating movements of the lungs, viz : expansion and 

 contraction, both of which will have an influence on the respiratory centre. 



Pos. ventilation 



Diaphragm 

 Seconds 



FIG. 524. Positive ventilation. (HEAD.) 



Under the influence of positive ventilation, the inspiratory contractions of the 

 diaphragm become less and less till they disappear completely. 



Neg. ventilation 

 Diaphragm 



FIG. 525. 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. 



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 these organs in 

 respiration. Let us consider, for instance, what will happen if the influence 

 of the two vagi could be suddenly thrown in after these nerves have been 

 divided. (This experiment can, in fact, be realised more or less completely 

 if the functional division of the vagi be effected by cooling or by ether 

 narcosis.) The animal would be breathing slowly and deeply. If at the 

 beginning of an inspiration the vagi became functional, the expansion of the 

 lungs caused by the inspiratory movement would send inhibitory impulses 



