EXHALATION OF WATERY VAPOR ETC. 149 



In a student rather above the ordinary height the quantity was 11,929 

 grains (773 grammes). 



The mean of his observations gave a daily exhalation of 8,333 grains (540 

 grammes), or about a pound and a half. 



The extent of respiratory surface has a marked influence on the quantity 

 of watery vapor exhaled. This fact is very well shown by a comparison of 

 the exhalation in the adult and in old age, as in advanced life the extent of 

 respiratory surface is much diminished. Barral found the exhalation in an 

 old man less than half that of the adult. It is evident that the absolute 

 quantity of vapor exhaled is increased when respiration is accelerated. The 

 quantity of water in the blood also exerts an important influence. Valentin 

 found that the pulmonary transpiration was more than doubled in a man 

 immediately after drinking a large quantity of water. 



The vapor in the expired air is derived from the entire surface over which 

 the air passes in respiration, and not exclusively from the air-cells. The air 

 which passes into the lungs derives a certain quantity of moisture from 

 the mouth, nares and trachea. The great vascularity of the mucous mem- 

 branes in these situations, as well as of the air-cells, and the great number 

 of mucous glands which they contain, serve to keep the respiratory surfaces 

 constantly moist. This is important, for only moist membranes allow the 

 free passage of gases, which is of course essential to the process of respira- 

 tion. 



Exhalation of Ammonia, Organic Matter etc. A small quantity of am- 

 monia is exhaled by the lungs in health, and this is increased in certain dis- 

 eases, particularly in uraemia. Its characters in the expired air are frequently 

 so marked, that patients who are entirely unacquainted with the pathology 

 of uraemia sometimes recognize an ammoniacal odor in their own breath. 



The pulmonary surface exhales a small quantity of organic matter. This 

 has never been collected in sufficient quantity for analysis, but its presence 

 may be demonstrated by the fact that a sponge completely saturated with the 

 exhalations from the lungs, or the vapor from the lungs condensed in a glass 

 vessel, will undergo putrefaction, which is a property distinctive of organic 

 substances. 



It is well known that certain substances which are but occasionally found 

 in the blood may be eliminated by the lungs. Certain odorous matters in 

 the breath are constant in those who take liquors habitually in considerable 

 quantity. The odor of garlics, onions, turpentine and of many other articles 

 taken into the stomach, may be recognized in the expired air. 



The lungs eliminate certain gases which are poisonous in very small 

 quantities when they are absorbed in the lungs and carried to the general 

 system in the arterial blood. Hydrogen monosulphide, which produces death 

 in a bird when it exists in the atmosphere in the proportion of one to eight 

 hundred, may be taken in solution into the stomach with impunity and even 

 be injected into the venous system ; in both instances being eliminated by 

 the lungs with great promptness and rapidity (Bernard). The lungs, while 

 they present an immense and rapidly absorbing surface for volatile poisonous 



