PHYSIOLOGY OF RESPIRATION. 661 



Physical Changes in the Expired Air. — ^The expired air is 

 warmed nearly or quite to the body temperature and is nearly 

 saturated with water vapor. Since, as a rule, the air that we 

 inspire is much cooler than the body and is far from being saturated 

 with water vapor, it is evident that the act of respiration entails 

 upon the body a loss of heat and of water. Breathing is, in fact, 

 one of the means by which the body temperature is regulated, 

 although in man it is a subsidiary means. In other animals — the 

 dog, for instance — panting is a very important aid in controlling the 

 body heat. Heat is lost in respiration not simply in warming the 

 air in the air passages, but also by the evaporation of water in the 

 alveoli, the conversion of water from the liquid to the gaseous form 

 being attended by an absorption of heat. Breathing is also one 

 of the means by which the water contents of the body are regulated. 

 The water that we ingest or that is formed within the body is kept 

 within certain limits, and this regulation is effected by the secretions 

 of urine and sweat mainly, but in part also by the constant loss of 

 water from the blood as it passes through the lungs. 



The Injurious Effect of Breathing Expired Air— Ventila- 

 tion. — It is generally recognized that in badly ventilated rooms the 

 air acquires a disagreeable odor, perceptible especially immediately 

 on entering, and that persons remaining under such conditions fo^: 

 any length of time suffer from headache, depression, and a general 

 feeling of uncomfortableness. It has been assumed, although 

 without sufficient proof, that these effects are due to the vitiation of 

 the atmosphere by the expired air. When the ventilation is very 

 imperfect and the room greatly crowded death may result, as, for 

 instance, in the historical case of the Black Hole of Calcutta. 



In India in 1756, when Fort William at Calcutta was taken from the 

 English by the Indian forces, some 146 persons were confined in the Black Hole 

 Prison, a small room, 18 x 14 x 10, during a sultry night in June — only 23 of 

 the captives were alive in the morning. The incident has been cited often as 

 an example of death from suffocation due to an insufficient supply of air, 

 but the pathetic description left by one of the survivors (A genuine Narrative 

 of the Deplorable Deaths of the English Gentlemen and others who were suf- 

 focated in the Black Hole in Fort Williams, at Calcutta, etc., by J. Z. Hol- 

 well, London, 1758) makes it probable that death was due to heat prostration 

 from the heat, moisture, and stagnant air. 



Under the ordinary conditions of life poor ventilation pro- 

 duces its obviously evil results in rooms temporarily occupied — 

 schools, churches, lecture rooms, theaters, etc. — and it is important 

 to know what is the cause, and how it may be avoided. On the 

 basis of older work it had been assumed that there is present in 

 the expired air a volatile organic substance which when breathed 

 again, possibly after having undergone some further change, ex- 

 erts a toxic influence. The evil effects of badly ventilated rooms 



