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 - 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 i 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 1S57, 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 Keiset 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," Ed. iv. 
Th. 2, S. 129, from which many of the figures in the above tables have been taken. See 
also tables in paper by Biehet, Arch, de physiol. norm, et path., Paris, 1891, tome xxiii. 
p. 74. 
- Article "Animal Heat," this Text-book, vol. i. p. 791. 
3 See p. 720. 
4 "On Animal Heat," London, 17S8, pp. 311, 3S7. 
5 Journ. dephys. de chim., etc., Paris, 1813, tome lxxvii. p. 5. 
6 Ztschr.f. Physiol., 1831, Bd. iv. S. 1. 
7 Journ. f. prakt . Chem., Leipzig, Bd. xxxiii. S. 152. 
' 8 Untersuch. z. Xatvrl. d. Mertsch. a. d. Thieve, 1857, Bd. ii. S. 315. 
9 Ann. de chim. etphys., Paris, 1849, Ser. 3, tome xxvi. 
