RESPIRATION 201 



curiously enough, broad-chested persons are not neces- 

 sarily well endowed in this respect. Disease affects it 

 very markedly, especially phthisis. Thus a man below 

 fifty-five whose capacity is only 193 cubic inches is 

 probably the subject of disease of the lungs. Curiously 

 enough, both pleurae may be entirely adherent all over 

 without in any way limiting the respiratory capacity. 



The vital capacity also varies greatly with posture. 

 Thus in the same man it was : 



260 cubic inches when standing. 

 255 ,, ,, sitting erect. 

 230 lying supine. 

 220 prone. 



HUTCHINSON. 



This shows how it is that patients with dyspnoea 

 cannot breathe when lying down. The diminution of 

 vital capacity as age advances is due to an increasing 

 difficulty in completely emptying the lungs on account 

 of thoracic rigidity. 



The Nervous Mechanism of Respiration. 



The mechanical part of the respiratory process is 

 controlled by an elaborate nervous apparatus, the head- 

 quarters of which are situated in the respiratory centre 

 in the medulla. This centre consists of two lateral 

 halves either of which is apparently able to act inde- 

 pendently of the other, for it is quite common for a 

 patient with disease of the lungs e.g., pleurisy to 

 breathe on one side only. There would also appear 

 to be independence of action as regards those parts of 



