THE REGULATION IN HEALTH AND DISEASE 565 



but not of carbon dioxide. The long periods of apnoea which 

 occur in hibernating mammals are replaced by continuous breath- 

 ing, when they are made to inspire air containing carbon dioxide, 

 and similar treatment will abolish in man the apnceic phase of 

 Cheyne- Stokes' s respiration. 



The respiratory movements appear from a review of the present 

 evidence to be regulated by the gaseous composition of the arterial 

 blood which supplies the respiratory centre in the medulla oblongata. 

 The necessary impulses are not carried by the vagus or sympathetic 

 nerves, for it is well known that after section of both vagi the 

 respirations, although slow and deep, are yet maintained rhythmi- 

 cally, it may be for months, and hyperpnoea can still be produced by 

 muscular activity or by inhalation of carbon dioxide. The view 

 that the regulation of the rate of alveolar ventilation depends 

 under normal conditions upon the pressure of carbon dioxide 

 in the respiratory centre offers a satisfactory explanation of the 

 normal rhythm, hyperpnoea, and apnoea. 



It is necessary, however, to point out that there are probably 

 other factors concerned in the regulation of respiration ; some 

 of these may be effective indirectly by altering the pressure of 

 carbon dioxide, others may act directly upon the excitability 

 of the respiratory centre. There is little doubt that a rise in the 

 temperature of the body will increase the rate of respiration ; 

 this is seen especially in the dog when he is exercised or exposed 

 to the heat of the sun, and forms an important means of regulating 

 the temperature of the body. In man, horses, and other animals 

 muscular work produces a rise in the internal temperature of 

 the body, and thus another factor besides carbon dioxide may 

 be concerned in hyperpnoea. 



Nervous impulses carried by the vagi either from the lungs 

 or the heart probably play an important part in the co-ordina- 

 tion of the action of the respiratory muscles and the heart, so 

 that an adequate supply of blood may be maintained through 

 the lungs for the rapid absorption of oxygen and the removal 

 of carbon dioxide. The value of training appears to be largely 

 due to the exercise of the heart and lungs in accommodation, 

 and economy of work. The effect of section of both vagi requires 

 further investigation from these standpoints, for Haldane and 

 Lorrain Smith found that arrest of inspiration by dilatation of 

 the lungs is produced in an animal with its nerves intact, even 



