LECT. VII. ANIMAL HEAT. 147 



of carbonic acid exhaled. The activity of the respiratory 

 movements, the density of the respired air, and the quan- 

 tity of carbon introduced in the aliments, ought to be in 

 proportion to each other, in order to preserve the materials 

 of the animal economy. Letellier has lately proved that, 

 with birds and guinea-pigs, the quantity of oxygen con- 

 sumed in respiration is smaller, in proportion as the 

 temperature of the air is higher. The carbonic acid ex- 

 haled at centig. [= 32 Fahr.] he found to be double 

 that produced at the temperature of + 15 to 20 centig. 

 [= 59 Fahr. to 68.] 



In those animals in which the activity of the respiratory 

 movements is greater, the capillary circulation more rapid, 

 and the quantity of the blood-globules more considerable, 

 the portion of the fat in their tissues is very small. This 

 is the case with birds, the hyena, and the tiger. If these 

 animals be allowed but little or no exercise, fat soon ac- 

 cumulates in their tissues. From the experiments of Tre- 

 viramus, we learn that, if their weights be equal, a cold- 

 blooded animal consumes ten times less oxygen than a 

 mammal, and nineteen times less than a bird. 



Finally, I think it important to notice the results of a 

 great number of experiments made by Boussingault, to de- 

 termine, by a comparison of the composition of the aliments 

 with that of the excrements, whether any azote be exhaled 

 during respiration by graminivorous animals. 



By taking the mean of his results, we find that a turtle- 

 dove consumes, in 24 hours, 5-10 grammes of carbon, and 

 in the same space of time gives out 18-70 grammes of 

 carbonic acid (i. e. 565-165 cubic inches,) and 0-16 gram- 

 mes of azote (i. e. 7-69 cubic inches.) The azote, there- 

 fore, is ins part of the volume of carbonic acid, a propor- 

 tion below that found by Dulong and Despretz. The 

 hydrogen consumed in one day is 0-07 gramme ; so that 



