248 ANIMAL HEAT. 



oxygen absorbed into the blood from the air in the lungs 

 were combined with carbon and hydrogen in the system, 

 and that as much heat were thus generated as would be 

 developed during the quick combustion of equal quantities 

 of oxygen and carbon, and of oxygen and hydrogen, still, 

 the whole quantity of heat produced would amount to only 

 from f to f of that which is developed during the same 

 space of time by carnivorous as well as herbivorous 

 animals. Despretz placed animals in a vessel surrounded 

 with water ; an uninterrupted current of air to and from 

 the vessel was maintained, and the volume and composition 

 of the air employed were ascertained both before and after 

 the experiment (which was continued i \ or 2 hours), as 

 well as the increase in the temperature of the surrounding 

 water during its progress ; by this means it was found 

 that the heat which should have been generated, accord- 

 ing to the chemical theory of respiration, would account for 

 from 0*76 to 0*91 only of that which the animals really 

 gave out during the same time. The failing of these 

 experiments to account for all the heat produced threw 

 doubts on the chemical theory of animal heat (as the pro- 

 posed explanation has been called), till Liebig showed that 

 Dulong and Despretz were in error in their conclusions, 

 from having formed too low an estimate of the heat pro- 

 duced in the combustion of carbon and hydrogen. On 

 repeating their experiments, and using the more accurate 

 numbers to represent these combustion-heats, Liebig found 

 reason to believe that the quantity of heat which would 

 be generated, by the union of the oxygen absorbed into 

 the blood from the atmosphere with the carbon and hydro- 

 gen taken into the system as food, would be sufficient to 

 account for the whole of the caloric formed in the animal 

 body. 



Many things observed in the economy and habits of 

 animals are explicable by this theory, and are, therefore, 

 evidence for its truth. Thus, as a general rule, in the 



