RESPIRATION 243 



from the blood and tissues. This change has no metabolic 

 significance. Indeed, the determination of the respiratory 

 quotient for short periods has only a limited value, and such 

 observations must be interpreted with great care. In starvation 

 the respiratory quotient diminishes, the production of carbon 

 dioxide falling off at a greater rate than the consumption of 

 oxygen, for the starving organism lives on its own fat and pro- 

 teins, and has only a trifling carbo-hydrate stock to draw upon. 

 In a diabetic patient, fed on a diet of fat and protein alone, the 

 respiratory quotient was only 0*6 to 0*7, just as in a starving man. 



The amount of oxygen absorbed in a man at rest has been 

 determined under certain conditions as about 0-29 gramme per 

 hour, and the discharge of carbon dioxide as about 0-33 gramme 

 per hour per kilogramme of body-weight. In an average man 

 weighing 70 kilos the mean production of carbon dioxide is about 

 800 grammes (400 litres) in twenty-four hours, and the mean 

 consumption of oxygen about 700 grammes (490 litres). But 

 there are very great variations depending upon the state of the 

 body as regards rest or muscular activity and on other circum- 

 stances. In hard work the production of carbon dioxide was 

 found to rise to nearly 1,300 grammes, and in rest to sink to 

 less than 700 grammes, the consumption of oxygen in the same 

 circumstances increasing to nearly 1,100 grammes and diminishing 

 to 600 grammes. In rest, in moderate exertion, and in hard work, 

 the production of carbon dioxide was found to be nearly pro- 

 portionate to the numbers 2, 3, and 6 respectively. When un- 

 accustomed work is performed, the increase in the carbon dioxide 

 output (and oxygen intake) may be much greater. With training 

 it diminishes. In a case of diabetes the consumption of oxygen 

 was 50 per cent, greater than in a healthy man, corresponding to 

 the higher heat-equivalent of the food of the diabetic patient. 



Ventilation. Taking 400 litres per twenty-four hours, or 

 17 litres per hour, as the mean production of carbon dioxide by 

 an average male adult at rest or doing only light w r ork, we can 

 calculate the quantity of fresh air which must be supplied to a 

 room in order to keep it properly ventilated. 



It has been found that when the carbon dioxide given off in 

 respiration amounts to no more than 2 parts in 10,000 in the air 

 of an ordinary room, the air remains sweet. When the carbon 

 dioxide given off reaches 4 parts in 10,000, the room feels dis- 

 tinctly, and at 6 in 10,000 disagreeably, close, while at 9 parts in 

 10,000 it is oppressive and almost intolerable. This has been 

 supposed by some to be due to a volatile poison exhaled from the 

 lungs, for pure carbon dioxide added alone in similar proportions 

 to the air of a room has not the same bad effect. Certain ob- 

 servers, indeed, alleged that the condensed vapour of the breath, 

 when injected into rabbits, produced fatal symptoms. But this 



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