130 RESPIRATION 



tient; and the less the proportion of oxygen to carbon dioxide, the 

 greater is the quotient. It is evident from this that the observations of 

 physiologists on the consumption of oxygen and the elimination of 

 carbon dioxide, when applied to the respiratory quotient, must undergo 

 some revision. 



The respiratory quotient is lowered by animal food and increased by 

 a vegetable diet. It is much lowered by fasting. 



The quotient is lower in children than in adults. 



The quotient is higher during the day than during the night. 



The quotient is much diminished during sleep. 



The quotient is much increased by muscular work. 



The quotient is much diminished by low external temperature. 



The quotient is much increased by breathing a mixture containing 

 twenty-one parts of oxygen and seventy-nine parts of hydrogen. 



Exhalation of Watery Vapor. From a large number of observations 

 on his own person and on eight others, collecting the water by sulphuric 

 acid, Valentin made the following estimates of the quantities of water 

 exhaled from the lungs in twenty-four hours : 



In his own person the exhalation in twenty-four hours was 5934 

 grains (384.48 grams). 



In a young man of small size the quantity was 5401 grains (350 

 grams). 



In a student rather above the ordinary height the quantity was 1 1,929 

 grains (773 grams). 



The mean of his observations gave a daily exhalation of 8333 grains 

 (540 grams), 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 well shown by a com- 

 parison 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 quantity of vapor exhaled is increased when respiration is ac- 

 celerated. 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 that passes into the lungs derives a certain quantity of moisture 

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

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

 number of mucous glands which they contain, serve to keep the respira- 



