122 RESPIRATION 



2.642 cubic inches (43.3 cubic centimeters). After taking the deepest 

 possible inspiration and holding the breath for a hundred seconds, the 

 percentage was increased 3.08 above the normal standard ; but the ab- 

 solute quantity was diminished more than fourteen cubic inches (229.4 

 cubic centimeters). Allen and Pepys noted that air which had passed 

 nine or ten times through the lungs contained 9.5 per cent of carbon 

 dioxide. 



Vierordt has given the following formula representing the influence 

 of the frequency of the respirations on the production of carbon dioxide : 

 Taking 2.5 parts per hundred as the constant value of the gas exhaled 

 by the blood, the increase over this proportion in the expired air is in 

 exact ratio to the duration of the contact of the air and blood. 



Among the most reliable observations on the quantity of carbon 

 dioxide exhaled by the human subject in a definite time and the varia- 

 tions to which it is subject, are those of Andral and Gavarret and of 

 Edward Smith. The observations of Lavoisier and Seguin, Prout, Davy, 

 Dumas, Allen and Pepys, Scharling and others, do not seem to have 

 fulfilled the necessary experimental conditions so completely. The ob- 

 servations of Andral and Gavarret were made on sixty-two persons of 

 either sex and different ages. and under identical conditions as regards 

 digestion, time of the day, barometric pressure and temperature ; and 

 the observations on males, between the ages of sixteen and thirty, be- 

 tween i and 2 P.M., under identical conditions of the digestive and mus- 

 cular systems, each experiment lasting eight to thirteen minutes, showed 

 an exhalation of about 1220 cubic inches (20 liters) of carbon dioxide 

 per hour. . 



Edward Smith employed the following method for the estimation of 

 the carbon dioxide exhaled : He used a mask, fitting closely to the face, 

 which covered only the air-passages. The air was admitted after having 

 been measured by an ordinary dry gas-meter. The expired air was 

 passed through a drying apparatus, and the carbon dioxide was absorbed 

 by a solution of potassium hydrate, arranged in a number of layers so as 

 to present a surface of about seven hundred square inches (45 square 

 decimeters), and was carefully weighed. This apparatus was capable of 

 collecting all the carbon dioxide exhaled in an hour. The estimates were 

 made for eighteen waking hours and six hours of sleep. The observa- 

 tions occupied ten minutes each and were made every hour and half- 

 hour for eighteen hours. The average for the eighteen hours gave 

 20,082 cubic inches (329 liters) of carbon dioxide for the whole period. 

 Observations during the six hours of sleep showed a total exhalation of 

 4126 cubic inches (7.145 liters). This, added to the quantity exhaled 

 during the day, gives as the total exhalation in the twenty-four hours, 



