EXCHANGE OF WARM-BLOODED ANIMALS. 709 



The respiratory exchange of warm-blooded animals. -The 

 tissues of warm-blooded animals are the seat of a very energetic 

 combustion, which is subject to quantitative and qualitative changes, 

 owing to the influence of certain factors, such as age, size of body, 

 external temperature, muscular activity, rest, digestion, hunger, and 

 hibernation. A general comparison between the various members of 

 the two great classes of the warm-blooded animals, birds and mammals, 

 will be found in the tables on pp. 706-708. 



These tables 1 show that, weight for weight, birds have a more 

 rapid respiratory exchange than mammals, and this difference is 

 associated with a higher bodily temperature. 2 It is also to be 

 noticed that the respiratory quotient of the herbivorous animals is 

 nearly unity, but that of the carnivorous animals is about 0*74. 

 The respiratory exchange of small animals of the same or of 

 different species is relatively greater than that of large animals. 3 

 The causes of many of these differences will now be discussed in 

 detail. 



The influence of external temperature upon the respiratory ex- 

 change. Since the time when Crawford 4 showed by experiment that 

 external cold increased the discharge of carbon dioxide from a warm- 

 blooded animal, numerous similar observations have been made by various 

 observers. The most important result of this work has been the dis- 

 covery that cold-blooded animals respond to changes of external tempera- 

 ture in an exactly opposite way to that shown by warm-blooded animals ; 

 in the former class a rise or fall in the temperature of the surroundings 

 produces respectively an increase or decrease in the intake of oxygen 

 and the output of carbon dioxide, whereas in the latter class cold increases 

 and heat diminishes the respiratory exchange. On this account it will 

 be well to consider separately the influence of temperature on these two 

 classes of animals, and then to discuss the causes of the great difference 

 in the effect. 



Cold-blooded animals. Some of the earliest experiments upon the 

 influence of temperature upon the respiratory exchange of cold-blooded 

 animals appear to have been made by Delaroche, 5 Treviranus, 6 and 

 Marchand, 7 but, owing to imperfect methods, their results are not very 

 exact, although they show that the respiratory exchange slowly rises 

 and falls with the external temperature. 



In 1857, Moleschott 8 made a series of experiments upon frogs, and 

 found that exposure to an increased external temperature or to light 

 caused an increase in the output of carbon dioxide. 



Eegnault and Eeiset 9 made three observations upon the respiratory 

 exchange of green lizards at different external temperatures, and obtained 

 the following results : 



1 Further data will be found in the article by Zuntz, Hermann's " Handbuch," Bd. iv. 

 Th. 2, S. 129, from which many of the figures in the above tables have been taken. See 

 also tables in paper by Richet, Arch, de pliysiol. norm, et path., Paris, 1891, tome xxiii. 

 p. 74. 



8 Article "Animal Heat," this Text-book, vol. i. p. 791. 



3 See p. 720. 



4 "On Animal Heat," London, 1788, pp. 311, 387. 



5 Journ. dephys. de chim., etc., Paris, 1813, tome Ixxvii. p. 5. 



6 Ztschr.f. Physiol., 1831, Bd. iv. S. 1. 



7 Journ. f. prakt. Chcm., Leipzig, Bd. xxxiii. S. 152. 



8 Untersuch. z. Natitrl. d. Mensch. u. d. Thiere, 1857, Bd. ii. S. 315. 



9 Ann. de chim. etphys., Paris, 1849, Ser. 3, tome xxvi. 



