244 A MANUAL OF PHYSIOLOGY 



has been shown to be erroneous ; and the most careful experi- 

 ments have failed to detect in the air expired by healthy persons 

 any trace of such a poison. It has therefore been suggested that 

 the odour and other ill-effects of a close room are due to sub- 

 stances given off in the sweat and the sebum, and allowed by 

 persons of uncleanly habits to accumulate on the skin, and also 

 to the products of slow putrefactive processes constantly going 

 on, under favourable conditions, on the walls, floor, or furni- 

 ture, but only becoming perceptible to the sense of smell when 

 ventilation is insufficient. 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 marked discomfort, with 

 dyspnoea, began to be felt. No close odour could be detected. 



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 ventila- 

 tion, 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 con- 

 sumed) is not only affected by muscular work, but also by every- 

 thing which influences the general metabolism. In males it 

 is greater on the average than in females (in the latter there is 

 a temporary increase during pregnancy), but for the same body- 

 weight and under similar external conditions there is no difference 

 between the sexes. The gaseous exchange is greater in pro- 

 portion to the body-weight in the child than in the adult. This 

 depends largely on the fact that, other things being equal, the 

 metabolism is relatively to the body-weight more active in a small 

 than in a large organism, since the surface (and therefore the 

 heat loss) is relatively greater in the former. But it has been 

 shown that even in proportion to the surface the metabolism is 



