142 CHANGES OF AIR AND BLOOD IN RESPIRATION. 



ured 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 decimetres), and was care- 

 fully 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 observations 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 litres) of carbon dioxide for 

 the whole period. Observations during the six hours of sleep showed a total 

 exhalation of 4,126 cubic inches (7*145 litres). This, added to the quantity 

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

 during complete repose, 24,208 cubic inches (about 14-24 cubic feet, or 

 336-145 litres), containing 7-144 oz. (202-47 grammes) of carbon. In view 

 of the great variations in the exhalation of carbon dioxide, this estimate can 

 be nothing more than an approximation. 



One of the important modifying influences is muscular exertion, by which 

 the production of carbon dioxide is largely increased. This would indicate 

 a larger quantity during ordinary conditions of exercise, and a much larger 

 quantity in the laboring classes. Dr. Smith has given the following approxi- 

 mate estimates of these differences : 



In quietude 7*144 oz. (202*47 grammes) of carbon. 



Non- laborious class 8*68 " (246*04 grammes) " 



Laborious class 11*7 " (331*61 grammes) " 



In studying the variations in the exhalation of carbon dioxide, important 

 imformation has been derived from experiments by many observers on the 

 inferior animals, as well as from the observations of Dumas, Prout, Scharling, 

 Pettenkofer and others, on the human subject. The principal conditions 

 which influence the exhalation of this principle are the following : Age and 

 sex ; activity or repose of the digestive system ; kind of diet ; sleep ; muscu- 

 lar activity ; fatigue ; moisture and surrounding temperature ; season of the 

 year. 



Influence of Age. In treating of the consumption of oxygen, it was stated 

 that during the first few days of extraiiterine existence, the demand for oxy- 

 gen on the part of the system is very small. At this period there is a corre- 

 spondingly feeble exhalation of carbon dioxide. It is well known that during 

 the first hours and days after birth, the new being has little power of generat- 

 ing heat, needs constant protection from changes in temperature, and the 

 voluntary movements are very imperfect. During the first few days, indeed, 

 the infant does little more than sleep and take the small quantity of colostrum 

 which is furnished by the mammary glands of the mother. While the ani- 

 mal functions are so imperfectly developed and until the alimentation be- 

 comes more abundant and the child begins to increase rapidly in weight, the 

 quantity of carbon dioxide exhaled is very small. 



After the respiratory function has become fully established, it is probable, 



