190 UNCONSCIOUS NERVOUS OPERATIONS 



270. Necessity of Ventilation. In each ordinary expira- 

 tion of an adult man, from twenty to thirty cubic inches 

 of air issue from the lungs, or in one hour about twelve 

 cubic feet. This air has been deprived of a large pro- 

 portion of its oxygen, which has been replaced chiefly by 

 carbon dioxide. This carbonic acid, while not itself poi- 

 sonous, at least in small quantities, is always associated 

 in expired air with waste products of organic life which 

 are so, and is a measure of their amount. To be fit for 

 breathing, air should not contain more than one fifth of one 

 per cent of carbon dioxide. Some authorities say one tenth. 



It is found that in quiet breathing a man gives out 

 something over 1000 cubic inches of carbon dioxide in an 

 hour. If hard at work, he will expire two or three times 

 as much. From 1000 to 3000 cubic feet of fresh air per 

 hour for each occupant of a closed room should be 

 supplied from outside the building, and in hospitals and 

 workshops the amount should often be much larger. Per- 

 sons vary greatly in their sensitiveness to impure air. 

 Many become accustomed by long usage to dwelling in 

 ill-ventilated rooms, and seem to suffer no immediate evil 

 effects ; when others coming from a purer atmosphere will 

 experience dizziness, headache, or nausea. 



271. Ventilation is the regular and continuous removal 

 of the expired, vitiated air from a room and the admis- 

 sion of pure atmospheric air. To be adequate to human 

 needs, it must bring into a room enough external air to 

 dilute the poisonous products of respiration and of the 

 combustion of gas, oil, or candles, together with the exha- 

 lations from the skin, to such a degree that the air of the 

 room may remain pure enough for breathing. 



The amount of air, by weight, inhaled by an average 

 person in twenty-four hours is from six to eight times 



