548 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



hour. All circumstances, such as muscular activity, which increase the output 

 of CO 2 augment the demand for fresh air. When confined in rooms, every 

 person should have an air-space equal to about 28,000 liters, or 1000 cubic 

 feet, the floor- space should not be less than ^ of the cubic capacity of the 

 room, and the air should be renewed as often as twice an hour. In lecture- 

 rooms, school-rooms, etc. the air-space per individual is usually very small, so 

 that the renewal must be more frequent and in proportion to the limitation of 

 space per individual. 



Ventilation is accomplished by natural and artificial means. The forces of 

 the wind, the differences in temperature within and without the building, the 

 natural diffusion of gases owing to variations in composition, etc., all cause 

 more or less circulation. Artificial ventilation is effected by the use of proper 

 appliances for the forced introduction of air into and expulsion from apartments. 



F. THE EFFECTS OF THE RESPIRATION OF VARIOUS GASES. 



The respiration of pure O takes place without disturbance of the respiratory 

 processes, but dyspnoea is developed when the inspired air contains less than 13 

 volumes per cent. (p. 543). Respiration of pure CO 2 (p. 544) is fatal within 

 two or three minutes, but an atmosphere containing as much as 25 to 30 per 

 cent, may be respired for a few minutes without ill effect (p. 544). Nitrogen, 

 hydrogen, and carburetted hydrogen (CH 4 ) may be inhaled with impunity if 

 they contain not less than 13 volumes per cent, of O. The respiration of 

 nitrous oxide or of air containing much ozone rapidly produces anaesthesia, 

 unconsciousness, and death. Carbon monoxide (CO) and cyanogen are decid- 

 edly toxic, combining with haemoglobin and displacing oxygen. Sulphuretted 

 hydrogen, phosphoretted hydrogen, arseniuretted hydrogen, and antimoniu- 

 retted hydrogen are all poisonous and are all destructive to haemoglobin. An 

 atmosphere containing 0.4 volume per cent, of sulphuretted hydrogen is said 

 to be toxic. Air containing 2 volumes per cent, of CO (carbon monoxide) is 

 quickly fatal. Certain gases and vapors as, for instance, ammonia, chlorine, 

 bromine, ozone,, etc. produce serious irritation of the respiratory passages, and 

 may in this way cause death. 



G. EFFECTS OF THE GASEOUS COMPOSITION OF THE BLOOD ON THE 



RESPIRATORY MOVEMENTS. 



Certain terms are employed to express peculiarities in the respiratory phe- 

 nomena : Eupncea is normal, quiet, and easy breathing. Apncea is a suspen- 

 sion of the respiratory movements. Hyperpncea is a condition of increased 

 respiratory activity. Polypncsa, thermopolypnoea, and heat-dyspnoea are forms 

 of hyperpnoea due to heating the blood or the skin. Dyspnoea is distinguished 

 by deep and labored breathing ; the respiratory rate is usually less than the 

 normal, but in some forms it may be higher. Asphyxia (suffocation) is cha- 

 racterized by infrequent, feeble, and shallow respirations. 



Eupncea is the condition of respiration observed during bodily and mental 



