CHAP. XXIX.] QUANTITY OF CARBON EXHALED. 413 



can be proved in the arterial and venous blood. Moreover, blood 

 may be caused to absorb, or to give up, these gases after it has 

 been removed from the body. 



All the tissues of the body contain a small quantity of dissolved 

 gases ; and carbonic acid can be detected in all the animal fluids, 

 even in the urine. 



Frogs' muscles, carefully deprived of nerves and vessels, will give 

 out carbonic acid if placed in an atmosphere of oxygen gas ; and 

 it has been shown by G. Liebig, that the muscles continue to ab- 

 sorb oxygen, and to exhale carbonic acid, as long as their power 

 of contractility lasts, and that they retain their contractile power 

 for a much longer period in an atmosphere of oxygen gas than in 

 one of hydrogen, nitrogen, etc. The careful observations of 

 Lehmann upon the respiration of insects (in which class the air is 

 directly carried to the elements of the tissues by the tracheae) , tend 

 still further to prove the truth of this view. We may, therefore, 

 conclude, that the oxygen of the air is carried by the blood to the 

 ultimate elements of the tissues, and that here chemical combina- 

 tion takes place and carbonic acid is produced ; the carbonic acid 

 being then transmitted to the lungs in solution in the venous blood, 

 and there exhaled. 



Quantity of Carbon removed from the Body. The estimation of 

 the amount of carbon eliminated from the organism in a given 

 time is a matter of great difficulty, and the results of the experi- 

 ments of observers present wide, differences. Allen and Pepys 

 calculated the daily quantity at rather more than 11 oz. troy, while 

 Mr. Coathupe estimated it at only 4- 9 7 ounces, and Scharling at 

 7-382 ounces. 



The method employed by Liebig consisted in subtracting the 

 total quantity of carbon in the faeces and urine from that present 

 in the food ; the remainder represented the quantity excreted in 

 the breath in the form of carbonic acid. Erom these data, Liebig 

 calculates that an adult male, taking moderate exercise, loses 13-9 

 ounces of carbon daily from the lungs and skin. In order to 

 convert this large quantity of carbon into carbonic acid, 37 ounces 

 of oxygen must be absorbed during the same period by the lungs 

 and skin ; but this estimate is doubtless too high. Andral and 

 Gavarret estimated the carbon at nine ounces. 



According to the recent accurate investigations of Scharling, a 

 powerful adult man exhales in the course of twenty-four hours 

 about 30*6 oz. of carbonic acid, which corresponds to 8'34 oz. of 

 carbon, and this we may look upon as a correct estimate. 



