RESPIRATION. 



345 



his experiments upon warm-blooded animals 

 and reptiles, found that in some cases the 

 quantity of azote in the air respired was 

 increased, in others diminished, while in 

 others it remained unchanged ; but these 

 changes in the quantity of azote did not equal 

 the difference between the amount of oxygen 

 absorbed and of carbonic acid exhaled. La- 

 voisier and Seguin*, Allen and Pepysf, Va- 

 lentin and BrunnerJ, and Dr. Thomson $, 

 in their experiments on the respiration in the 

 human species, detected no change upon the 

 quantity of azote.|| Boussingaultl, by a 

 series of comparative analyses of the aliments 

 consumed, and of the excrements in a turtle- 

 dove, arrived at the conclusion by this in- 

 direct method of research that azote was 

 exhaled. 



Marchand**, in his carefully-conducted ex- 

 periments on frogs, detected a quantity of 

 ammonia in the tube of his apparatus, con- 

 taining the concentrated sulphuric acid, and 

 concludes that nitrogen in this combination is 

 exhaled from the lungs and skin. 



From a review of all the experiments upon 

 the nitrogen of the respired air, we perceive 

 that though the evidence preponderates in 

 favour of the exhalation of a small quantity 

 of nitrogen from the lungs ft, yet that it is not 

 sufficiently conclusive to justify us in stating 

 that its operation is constant. It appears, 



* Mem. de 1' Academic Eoyale for 1789, p. 574. 



f Opus cit. 



j Opus cit. 



Animal Chemistry, p. 612. 1843. Dr. Thom- 

 son says, in experimenting upon animals placed in 

 vessels in which the air was renewed during the 

 experiment, no diminution of the volume of air took 

 place, but the case was very different when the 

 animal was obliged to breath confined air. Nysten 

 (Opus cit. p. 230) observed an evolution of azote in 

 the human species, both in a state of health and 

 disease, when the same air was breathed several 

 times. Marchand, on the other hand (Journal fur 

 praktische Chemie, band xxxiii. S. 166), from his 

 experiments on frogs placed in close vessels, con- 

 cludes that it is exceedingly probable, if not certain, 

 that, under this condition, these animals absorb part 

 of the azote of the atmospheric air. 



|| Vierordt remarks upon Valentin and Brunner's 

 experiments, and the same observation applies to 

 to the others on the human species, that the evolu- 

 tion of a minute quantity of nitrogen, not readily 

 detected during the short time each of these experi- 

 ments was carried on, might amount to a notable 

 quantity in the 24 hours. 



^f Annales de Chimie et de Physique, torn. xi. 

 p. 433. 1844. In taking the mean of the result of 

 his experiments, he found a turtle-dove, weighing 

 2885-971 English Troy grains, evolved in 24 hours 

 from the lungs 288-597 grains of carbonic acid gas, 

 and 2-469 grs. of azote, or in volume 576-155 English 

 cubic inches of carbonic acid and 7-689 cubic inches 

 of azote, a considerably smaller quantity than was 

 obtained by Dulong and Despretz in their experi- 

 ments by the direct method. This quantity of azote, 

 according to Boussingault, constitutes the one-third 

 of the whole of this substance which entered into 

 the composition of the aliment of the pigeon. 



** Opus cit. 



ft It must, however, be remembered that in the 

 great majority and in the most trust-worthy of these 

 experiments in favour of the increase of the nitrogen, 

 the exhalations from the skin were mixed with 

 those from the lungs. 



however, from the evidence adduced, that 

 the nitrogen in the expired air is at least 

 frequently increased in quantity in ordi- 

 nary respiration, but not to the extent of 

 affecting materially the percentage of this gas 

 in the respired air.* Valentin and Brunner, 

 in their carefully conducted experiments, could 

 detect no traces of hydrogen, carbonic oxide, 

 or carburetted hydrogen, in the expired air. 



By far the most important chemical change 

 the atmospheric air undergoes during its so- 

 journ in the lungs, is a diminution in the 

 quantity of its oxygen and an increase of its 

 carbonic acid gas ; and it may be safely af- 

 firmed that all the other changes in the 

 respired air are of trivial importance in the 

 function of respiration, when compared with 

 this. There can be no doubt that the con- 

 clusion drawn by Allen and Pepys from their 

 experiments, that the amount of oxygen 

 which disappears from the inspired air is 

 exactly equal to the quantity required to form 

 the carbonic acid that appears in the expired 

 air, is incorrect ; for all the latest and most 

 accurate experiments have confirmed the 

 general accuracy of the results obtained by 

 Lavoisier and Davy on this point, and have 

 satisfactorily determined that a larger quantity 

 of oxygen disappears from the inspired air 

 than what is sufficient to form the carbonic 

 acid gas present in the expired air. 



Percentage and absolute quantity of carbonic 

 acid gas in the expired air. The results of 

 the earlier experimenters on this point are of 

 so little value that we need not refer to them. 

 The following results have been obtained by 

 some of the later experimenters: 



QUANTITY OF CARBONIC ACID GAS IN THE 100 PARTS 

 OF THE EXPIRED AIR ESTIMATED BY VOLUME. 



* Even supposing the nitrogen of the respired air 

 to remain unaltered in quantity, yet as the quantity 

 of oxygen absorbed is somewhat greater than what 

 is necessary to form the carbonic acid exhaled along 

 with the expired air, the percentage of the nitrogen 

 in the inspired air will be slightly greater than in 

 the expired air when estimated by volume. 



f Thomson's Annals of Philosophy, vol. ii. p. 333. 

 1813. In some subsequent experiments by Trout 

 (same work, vol. iv. p. 331) the range in the quan- 

 tity of carbonic acid gas in the expired air was be- 

 tween 2-80 and 4-70, the minimum number occurring 

 once only, and while he was sleepy. Prout's expe- 

 riments were performed upon himself, and at everv 

 hour of the day and night. 



J London, Edinburgh, and Dublin Philosophical 

 Magazine, vol. xiv. p. 401. 1839. These expert- 



