218 RESPIRATION. 



But Dr. Edwards has since shown that, however correct were 

 these results, it was erroneous to generalise from them; that more 

 oxygen is continually consumed by brutes than goes to the form- 

 ation of carbonic acid ; and that this excess varies from above \ of 

 the volume of the latter to almost nothing.* The variation de- 

 pends not only upon the species, but upon the developement re- 

 lative to the age, and upon individual differences in adults. 



He therefore finds that the bulk of the air is not unaffected by 

 respiration, but that generally a diminution takes place. Dr. Le 

 Gallois b and Dr. Delaroche c also found that oxygen disappeared 

 in greater quantity than carbonic acid was formed. 



Allen and Pepys observed that, if the same air was breathed 

 repeatedly, some oxygen was absorbed and some azote discharged, 

 and that, if nearly pure oxygen was employed in the case of 

 guinea-pigs, carbonic acid was produced and a portion of the oxy- 

 gen replaced by azote, this portion decreasing, however, as the 

 experiment proceeded. 



Dr. Edwards ascertained that respiration causes sometimes an 

 increase of azote, sometimes a diminution, and sometimes no im- 

 portant difference in its quantity. He thinks that it is always being 

 absorbed and discharged, and that the proportion of these pro- 

 cesses differs under different circumstances. Its discharge exceeds 

 at all times in very young animals, as seen in guinea-pigs ; and in 

 spring and summer; while its absorption exceeds in autumn and 

 winter, as far as his experiments upon adult sparrows and yellow- 

 hammers go; though occasional exceptions occurred from unappre- 

 ciated circumstances, powerful enough to overbalance the effect 

 of season. d The difference in the proportion of the inspired and 

 expired azote never equalled the greatest differences observed 

 between the oxygen which disappeared and the carbonic acid 

 formed. Cold-blooded quadrupeds were shown by Spallanzani e 

 to absorb azote, and fish by Humboldt and Provencal. f Sir 

 Humphry Davy had already ascertained the absorption of azote 

 in his own person. 



Dr. Edwards's reasons for believing azote to be constantly both 

 absorbed and discharged are : 



a De V Influence des Agens Physiques sur la Vie. Paris, 1824. p. 410. sqq. 



b Annales de Chimie et Physique, t. iv. p. 115. sq. 



e Journal de Physique, t. 77. 



d 1. c. p. 420. sqq. 461. sqq. 



e Memoires sur la Respiration, pp. 184. 258. 



f Mtmoires d 'Arcueil, t. ii. 



