BLOOD. 125 



the loss has been variously estimated by Berthollet, Pfaff, and 

 Davy at from l-27th to 1-lOOth of its bulk. Allen and Pepys, 

 however, found the loss not more than l-16Gth, or about 0-6|^, 

 and they looked upon the former as a mere error of obser- 

 vation. 



The most important experiments regarding the changes 

 which atmospheric air undergoes in respiration, are those of 

 Allen and Pepys/ of Dulong,^ and of Despretz.^ 



The earlier experiments of Allen and Pepys showed that 

 the quantity of oxygen lost was exactly replaced by the car- 

 bonic acid generated, and that nitrogen was given off. 



In their later experiments, it appeared that more oxygen 

 was absorbed than the quantity of carbonic acid expired ac- 

 counted for ; they were also further con^dnced of the accuracy 

 of their former observations respecting the increased quantity 

 of nitrogen which is expired. They caused animals to breathe 

 an atmosphere of pure oxygen, and likewise of oxygen mixed 

 with three times its volume of hydrogen. In the latter case 

 a portion of the hydrogen disappeared, and was replaced by an 

 equal volume of nitrogen. 



The experiments of Dulong were conducted with great ac- 

 curacy, and by means of apparatus expressly prepared for the 

 purpose. They showed that more oxygen is consumed than is 

 replaced by the carbonic acid formed. The quantity of oxygen 

 thus lost, and not replaced by carbonic acid, amounted in the 

 case of herbivorous animals to about 10^ of the oxygen which 

 was changed into carbonic acid; in carnivorous animals the 

 minimum excess amounted to 20, and the maximum to 50^. 



The observations of Despretz confii'm the results obtained 

 by Dulong, and hkewise show that nitrogen is developed 

 during respiration. 



The following table presents a sketch of the results of the 

 observations made by Despretz ; the calculations are founded 

 on the French litre : — 



' Schweiger's Journal, vol. 1, p. 182; and vol. 57, p. 337. PliU. Trans. 1809, 

 p. 410. 



2 lb. vol. 38, p. 505. 



^ Aunales de Chimie et de Physique, vol. 26, p. 337. 



