237 



blooded animals possess. It is now very generally 

 allowed, that the caloric given out during the com- 

 bustion of bodies, is, like that obtained in respira- 

 tion, derived from the changes which the oxygen 

 gas of the air is made to undergo. When, there- 

 fore, equal quantities of oxygen gas are' converted 

 into carbonic acid by combustion and by respiration, 

 equal quantities of caloric may be expected to be 

 set free ; and this opinion, too, Dr Crawford at* 

 tempted by experiment to establish. He found, 

 'that 100 ounce measures of oxygen gas, changed 

 into carbonic acid by the respiration of a guinea-pig, 

 shut up in a close vessel, communicated to 31 lb, 

 7 oz. troy of water, surrounding that vessel, 17.3 

 of heat ; while the same quantity of oxygen gas, 

 converted into the same acid by the burning of 

 charcoal, communicated to a like quantity of water 

 19.3 of heat; and he concluded, therefore, that, 

 somewhat more heat was produced by the combus- 

 tion of charcoal, than by the respiration of an ani- 

 mal *. M. Lavoisier, likewise, made experiments 

 of a similar nature, but he substituted the melting of 

 ice, as a measure of the comparative heat given out 

 by respiration and combustion, for the raising of the 

 temperature of water ; and the conclusion which he 

 drew, when equal quantities of oxygen gas were 

 changed into carbonic acid by the respiration of a 

 guinea-pig and the combustion of charcoal, made 

 the quantity of heat produced by the animal, exceed 

 that by the combustion of charcoal in the propor- 



* On Animal Heat, p. 351. 



