666 PHYSIOLOGY OF RESPIRATION. 



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 for 

 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 

 extreme cases of this latter kind it is most probable that several 

 causes combine to produce a fatal result. The conditions are such 

 as to lead to a very large increase in carbon dioxid and diminution 

 of oxygen in the respired air a result which carried to a certain 

 point will itself cause death; and in addition the air becomes 

 heated to a high temperature and saturated with water vapor, 

 both of these latter conditions preventing loss of heat from 

 the body and producing a fever temperature. Under the or- 

 dinary conditions of life poor ventilation produces its ob- 

 viously 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 has 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, exerts a toxic influence. The 

 evil effects of badly ventilated rooms have been attributed mainly 



