THE CHEMISTRY OF EXTERNAL RESPIRATION 2 4 t 



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 07, just as in a starving man. 

 Total Respiratory Exchange. 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' 

 *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 proportionate to the numbers 

 2, 3, and 6 respectively. When unaccustomed 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 work, 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 distinctly, and at 6 in 10,000 disagree- 

 ably, close, while at 9 parts in 10,000 it is oppressive and almost in- 

 tolerable. This is not due to the carbon dioxide as such, for pure 

 carbon dioxide added alone in similar proportions to the air of a room 

 has not the same bad effect, and the amount of this gas is only taken 

 as an index of the extent to which the air has been vitiated by some 

 other products or processes connected with the occupation of the 

 room. Very often the mere rise of temperature in a crowded and ill- 

 ventilated space is sufficient to induce disagreeable symptoms, especially 

 as it is inevitably associated with an increase in the humidity of the 

 air, which reduces the capacity of the body to cool itself by increasing 

 the secretion of sweat. Thus it has been found that persons in a 

 respiratory chamber feel quite comfortable with only moderate ventila- 

 tion when the carbon dioxide has risen to I per cent., if care is taken 

 that the temperature and * he 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 



