526 OF RESPIRATION. 



kidneys. It also appears, from the recent experiments of Dr. Bence Jones, 1 

 that the action of oxygen is exerted in the system upon Ammonia, and probably 

 upon other products of decomposition of the nitrogenous tissues, in such a 

 manner as to produce Nitrous or Nitric acid, which makes its appearance in 

 the urine. 



564. The absolute quantity of Carbonic Acid exhaled from the Lungs is liable 

 to variation from so many sources, that no fixed standard can be assigned for it. 

 The mean of a great number of observations, however, made in different modes, 

 and under different circumstances, would give about 160 grains of Carbon per 

 hour as the amount set free by a well-grown adult man, under ordinary circum- 

 stances. Taking this as the average of the twenty-four hours, the total quantity 

 of Carbon thus daily expired from the Lungs would be 3840 grains, or 8 oz. Troy. 

 The chief causes of variation are the Temperature of the surrounding Medium, 

 Age, Sex, Development of the body, state of Health or Disease, Muscular Ex- 

 ertion or Repose, Sleep or Watchfulness, Period of the Day, and state of the 

 Digestive process. These will now be considered in detail. 



a. Temperature of 'surrounding Medium. The amount of Carbonic Acid 

 exhaled by warm-blooded animals is greatly increased by external Cold, and 

 diminished by Heat; as is shown by the following results of comparative ex- 

 periments upon the quantity set free by the same animals, at low, medium, and 

 high temperatures, in periods of an hour (Letellier 3 ) : 



Tern, about 32. Tern. 59 68. Tern. 86 106. 



Grammes. Grammes. Grammes. 



A Canary . ' .'".', . 0.325 0.250 0.129 



A Turtle-Dove .. .. . 0.974 0.684 0.336 



Two Mice ':.' V . 0.531 0.498 0.268 



A Guinea-Pig . .' ''!' . 3.006 2.080 1.453 



From this table it appears that the quantity of carbonic acid exhaled by Mam- 

 mals between 86 and 106 is less than half that set free near the freezing- 

 point; whilst that which is exhaled between 59 and 68 is but little more than 

 two-thirds of the same amount. The diminution occasioned by heat is still 

 more remarkable in Birds which exhale at the highest temperature scarcely more 

 than one-third of that set free at the lowest. The observations of Vierordt 3 

 upon himself show that the same is true of the Human subject ; a difference of 

 10 Fahr., according to him, producing a variation of rather more than two 

 cubic inches in the amount of Carbonic Acid hourly expired. 



b. Age. The amount of Carbonic Acid exhaled increases in both sexes up to 

 about the thirtieth year ; it remains stationary until about the forty-fifth ; and 

 then diminishes. The following are the comparative results of experiments 

 upon males of different ages, and of a moderate degree of muscular development 

 (Andral and G-avarret 4 ) : 



Carbon exhaled Carbon exhaled 



Age. per hour. Age. per hour. 



8 years 

 12 " 

 14 " 

 20 " 

 26 " 



77.0 grains. 37 years 164.7 grains. 



113.9 " 48 " 161.7 " 



126.2 " 59 " 154.0 " 



166.3 " 68 " 147.8 " 



169.4 76 " 92.4 " 



c. Sex. At all ages beyond eight years, the exhalation is greater in Males 

 than in Females. Nearly the same proportionate increase takes place, however, 

 in Females, up to the time of puberty ; when the quantity abruptly ceases to 



1 " Philosophical Transactions," 1851 ; and " Medical Times," Aug. 30, 1851. 



2 " Annales de Chimie et de Physique," 1845. 



3 "Physiologic des Athmens," pp. 73-82. 



4 " Annales de Chimie et de Physique," 1843. 



