RESPIRATION 227 



the products of slow putrefactive processes constantly going on, under 

 favourable conditions, on the walls, floors or furniture, but only 

 becoming perceptible to the sense of smell when ventilation is in- 

 sufficient. In a small, newly-painted chamber, presumably free 

 from such impurities, it was not until the carbon dioxide reached 

 3 to 4 per cent, that discomfort began to be felt and the respiration 

 to be quickened.* No close odour could be detected (Haldane and 

 Lorrain Smith). 



Nevertheless, experience has shown that it is a good working rule 

 for ventilation to take the limit of permissible respiratory impurity 

 at 2 parts of carbon dioxide per 10,000; and the 17 litres of carbon 

 dioxide given off in the hour will require 85,000 litres (or 3,000 cubic 

 feet) of air to dilute it to this extent. This is the average quantity 

 required for the male adult per hour. For men engaged in active 

 labour, as in factories or mines, twice this amount may not be too 

 much. For women and children less is required than for men. If a 

 room smells close, it needs ventilation, whatever be the proportion of 

 carbon dioxide in the air. 



It must be remembered that in permanently-occupied rooms mere 

 increase in the size will not compensate for incomplete renewal of the 

 air, although it may be easier to ventilate a large room than a small 

 one without causing draughts and other inconveniences. But as few 

 apartments are occupied during the whole twenty-four hours, a large 

 room which can be thoroughly ventilated in the absence of its 

 inmates has a distinct advantage over a small one in its great initial 

 stock of fresh air. 



The cubic space per head in an ordinary dwelling-house should be 

 not less than 28 cubic metres or 1,000 cubic feet. 



The quantity of carbon dioxide given off (and of oxygen 

 consumed) is not only affected by muscular work, but also by 

 everything which influences the general metabolism. In 

 males it is greater than in females (in the latter there is a 

 temporary increase during pregnancy), and greater in pro- 

 portion to the body-weight in the young than the old. This 

 depends, partly at least, on the fact that the metabolism is 

 relatively more active in a small than in a large organism. 

 The taking of food increases it, chiefly in consequence 

 of the increased mechanical and chemical work per- 

 formed by the alimentary canal and the digestive glands. 

 Sleep diminishes the production of carbon dioxide partly 



* Hyperpncea from defect of oxygen also appears when the amount of 

 it in the air has fallen to a point which varies in different individuals (in 

 one case 12 per cent.). Warm-blooded animals confined in a small air- 

 space die from want of oxygen, and not from the accumulation of carbon 

 dioxide ; but the opposite appears to be the case with cold-blooded 

 animals. 



152 



