146 RESPIRATION. 



entrance of air but was provided with a valve preventing its escape. By another open- 

 ing, the mask was connected by a rubber tube with three glass balloons, capable of hold- 

 ing 8,544 cubic inches, in which a vacuum had been previously established. With the mask 

 fixed upon the face, and a stopcock opened, connected with the balloons, so as to gradu- 

 ate the current of air, the subject respires freely in the current which comes from the 

 exterior into the receivers. In this way, although the quantity of air respired is not meas- 

 ured, the vacuum in the receivers draws in the products of respiration. The current will 

 continue for from eight to thirteen minutes and is so regulated that the air is respired 

 but once. The quantity of carbonic acid in the receivers represents the quantity pro- 

 duced during the time that the experiment has been going on. By carefully fulfilling all 

 the physiological conditions, regulating the number of respirations, as far as possible, to 

 the normal standard, different observations on the same subject, at different times and under 

 the same conditions, were attended with results so nearly identical as to give every con- 

 fidence in the accuracy of the process. But even then, these observers recognized such 

 immense variations in the exhalation of carbonic acid with the constantly-varying physi- 

 ological conditions, that they did not feel justified in taking their observations as a basis 

 for calculations of the entire quantity exhaled in the twenty-four hours. 



The results of the above-mentioned observations on the male, between the ages of six- 

 teen and thirty, between 1 and 2 P. M., under identical conditions of the digestive and 

 muscular systems, each experiment lasting from eight to thirteen minutes, showed an 

 exhalation of about 1,220 cubic inches of carbonic acid per hour. 



Dr. Edward Smith, in his elaborate paper on the phenomena of respiration, employed 

 a very rigorous method for the estimation of the carbonic acid exhaled. He used a mask, 

 fitting closely to the face, which covered only the air-passages. The air was admitted after 

 being measured by passing through an ordinary dry gas-meter. The expired air was passed 

 through a drying apparatus, and the carbonic acid was absorbed by a solution of potash, 

 arranged in a number of layers so as to present a surface of about seven hundred square 

 inches, and carefully weighed. This apparatus was capable of collecting all the carbonic 

 acid exhaled in an hour. The estimate was made for eighteen waking hours and six hours 

 of sleep. The observations for the eighteen hours were made on four persons; namely, 

 Dr. Smith, get. 38 years, weighing 196 pounds, 6 feet high, with a vital capacity of 280 

 cubic inches ; Mr. Moul, ret. 48 years, 5 feet 9 inches high, 1V5 pounds weight ; Dr. 

 Murie, set. 26 years, 5 feet 7|- inches high, 133 pounds weight, vital capacity 250 cubic 

 inches ; Prof. Frankland, set. 33 years, 5 feet 10 inches high, and 136 pounds weight. 

 Breakfast was taken at 8^ A. M., dinner at 1^, tea at 5|-, and supper at 8^ p. M. The ob- 

 servations occupied ten minutes and were made every hour and half-hour for eighteen 

 hours. The average for the eighteen hours gave 20,082 cubic inches of carbonic acid for 

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

 of 4,126 cubic inches. 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), containing T144 oz. av. of carbon. Considering the great varia- 

 tions in the exhalation of carbonic acid, this estimate can be nothing more than an ap- 

 proximation. One of the great modifying influences is muscular exertion, by which the 

 production of carbonic acid 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 gives the following approximate estimates of these differences : 



In quietude 7'144 oz. av. of carbon. 



Non-laborious class 8'68 " " 



Laborious class 11'7 " " 



In studying the variations in the exhalation of carbonic acid, important information 

 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 



