1104 PHYSIOLOGY 



acid, sulphuretted hydrogen, phosphuretted hydrogen (PH S ), arseniuretted 



hydrogen, &c. 



IRRESPIRABLE GASES are those which are so irritating that they pro- 

 duce spasm of the glottis. Such are ammonia, chlorine, sulphur dioxide, 

 nitric oxide, and many others. 



VENTILATION 



A point of practical importance is the securing to each individual of 

 sufficient fresh air, so that he may always have a plentiful supply of oxygen, 

 and may be relieved of his waste products. It is found that a dwelling-room 

 becomes unpleasant and stuffy when the percentage amount of C0 2 has 

 reached 0-1 per cent. This stuffiness is supposed to be due to organic 

 exhalations from the skin, lungs, and alimentary canal, some of which have 

 a poisonous effect, giving rise to headache and sleepinesss. Since these 

 cannot be measured, it is taken as a cardinal rule in ventilation that the 

 amount of C0 2 should never rise above 0*1 per cent. 



Since in questions of ventilation we have generally to deal with trades in 

 which the metric measure is not used, it may be convenient to give the data 

 as to carbon dioxide production and the amount of air required in cubic 

 feet. 



An adult man gives off about 0-6 cubic foot of C0 2 every hour. Hence 

 in that time he raises the amount of C0 2 in 1000 cubic feet of air from -04 

 per cent, (the normal amount in the atmosphere) to O'l per cent. He must 

 therefore be supplied with 2000 cubic feet of air per hour in order to keep 

 the amount of CO 2 down to -07 per cent. 



(Ordinary air contains -04 per cent. C0 2 , therefore 2000 cubic feet would 

 contain 0-8 cubic foot C0 2 , which with the 0-6 cubic foot.given off by the man 

 would be 1-4, which is -07 per cent.) 



In order that the air may be easily renewed without giving rise to exces- 

 sive draught, a certain amount of cubic space must be allotted to each man. 

 Each adult should have in a room 1000 cubic feet of space, and be supplied 

 every hour with 2000 to 3000 cubic feet of air. 



