406 RESPIRATION. [CHAP. XXIX. 



The general average of the results of Valentin and Brunner, and 

 Vierordt, all of which were performed on adult males, may be 

 accepted for that age and sex, viz., 4'35 parts of carbonic acid in 

 100 parts of expired air ; or deducting the small quantity of car- 

 bonic acid contained in the air when inspired, we may conclude 

 that 4'30 parts per cent, by volume of that gas are derived from 

 the lungs at each ordinary expiration. Taking, as before, 30 

 cubic inches as the volume of each expiration, the actual quantity 

 of carbonic acid in each will be 1*29 cubic inches=about 23 cubic 

 inches per minute=about 1393 cubic inches per hour = about 27,864 

 cubic inches, or 16*1 cubic feet per day. In this last quantity of 

 carbonic acid there are about seven and a half ounces by weight 

 of carbon. 



A great variety of circumstances, no doubt, modify the activity 

 with which carbonic acid is formed in the system, and eliminated 

 from it ; some of these are very worthy of notice. Digestion has 

 been observed to be attended with an increased exhalation of it in 

 many of the lower animals ; and Scharling, Valentin, and Vierordt 

 have recently noted the same fact with great accuracy in Man. 

 Thus, one hour after a midday meal, Vierordt found that his. pulse 

 was quickened by 15, his respiration by 1, the volume of the 

 expired air was slightly increased, nearly 50 per cent, more of air, 

 and 2 1 cubic inches more of carbonic acid were expired in one 

 minute, and the per centage of carbonic acid in the expired air was 

 also augmented in a very trifling degree. If the meal were omitted 

 these results did not occur. On the other hand, fasting, especially 

 if prolonged, diminishes the exhalation. 



Particular substances taken into the blood, exert a very remark- 

 able influence upon the development of carbonic acid in the system. 

 Dr. Prout long since observed a considerable diminution under 

 alcohol, particularly if taken on an empty stomach ; and his con- 

 clusions have been fully confirmed by Vierordt and Bocker. The 

 former found, that, having taken more than half a bottle of wine, 

 the carbonic acid fell in a quarter of an hour from 4*54 to 4'01 per 

 cent, of the expired air ; i.e., by about one-ninth of its whole 

 quantity ; and this lasted for two hours. In addition to this, the 

 latter author found that, under the same influence, the whole con- 

 stituents of the urine are diminished in amount. Dr. Prout states 

 that a dose of strong tea likewise lessens the exhalation of carbonic 

 acid. 



Since the introduction of ether and chloroform as anaesthetics in 

 the practice of surgery, their mode of action has been much inves- 





