THE CHEMISTRY OF EXTERNAL RESPIRATION 243 



that the temperature and the proportion of watery vapour do not rise 

 too high. In addition, however, it has been supposed by some that a 

 volatile poison exhaled from the lungs is peculiarly responsible for the 

 evil effects. Certain observers, indeed, alleged that the condensed 

 vapour of the breath, when injected into rabbits, produced fatal symp- 

 toms. But this has been shown to be erroneous; and the most careful 

 experiments 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 some of the 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 furniture, but only becoming per- 

 ceptible 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., an immensely 

 greater proportion than occurs even in very badly ventilated rooms, 

 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 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 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 proportion 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 greater in youth than in adult life, and 

 greater in the vigorous adult than in the old man. So that the age 

 of the organism has an influence apart from the extent of surface. 

 The taking of food increases the gaseous exchange, partly from the 



