RESPIRATORY MOVEMENTS 85 



cord) or if gas-exchange in the placenta (by premature rupture 

 of the placenta) is prevented, lack of oxygen and accumulation of 

 carbon dioxide in the blood of the embryo takes place. This can 

 bring about respiratory movements before birth. 



If, by lack of aeration, the arterial blood becomes poorer 

 in oxygen and richer in carbon dioxide than the normal 

 blood, respiration is increased, the inspirations becoming 

 deeper and more frequent dyspnoea. Strong continued 

 dyspnoea finally produces death through paralysis of the 

 respiratory centre suffocation, asphyxia. 



The normal stimulation of the respiratory centre by lack 

 of oxygen and accumulation of carbon dioxide serves to 

 regulate the intensity of the respiratory movements accord- 

 ing to the need of the organism. 



In the active muscle there are supposed to be formed other 

 products besides the carbon dioxide which stimulate the respiratory 

 centre. 



Many authors suppose that the carbon dioxide does not only 

 stimulate the centre directly but also indirectly, in that it stimu- 

 lates the endings of the centripetal nerves in the tissue where it 

 is formed, and these in turn reflexly increase the respiration. 



Increase of temperature augments the action of the 

 respiratory centre heat dyspnoea (e.g. in fever). 



2. Indirect stimulation of the respiratory centre is pro- 

 duced by stimulations carried to the centre by nerves. 



(a) From the cerebral hemispheres, psychical influences 

 can modify the number, depth, and rhythm of inspirations. 

 On the one hand, we can, to a certain extent, voluntarily 

 influence respiration ; while, on the other hand, respiration 

 is involuntarily influenced by the emotions (fear, anger, 

 etc.). 



() Reflex modifications of respiration are, e.g., the expul- 

 sive expirations which are called sneezing and coughing and 

 are produced by the stimulation of the sensory nerves of the 

 mucous membrane of the nose (trigeminus) and of the larynx 

 (superior laryngeal). Besides these respiration is reflexly 

 influenced by a large number of other sensory stimuli. 



