f OF ANIMAL HEAT. 115 



the air and forms carbonic acid, the smaller capacity of this than 

 of common air for caloric, must cause an increase of tempera- 

 ture, but the blood, having changed from venous to arterial, has 

 acquired a greater capacity than before and absorbs the heat given 

 out by the carbonic acid. The blood, of course, does not become 

 warmer, because the heat is not more than sufficient to render 

 its temperature equal to what it was previously ; and indeed 

 it is not quite sufficient for this, since the arterial blood of the 

 pulmonary veins is generally two degrees lower than that of the 

 pulmonary artery. 



The body in this way acquires a fund of heat, and yet the 

 lungs, in which it is acquired, do not experience any elevation 

 of temperature. 



The arterial blood, charged with much heat which is not sen- 

 sible, as it circulates through the small vessels, becomes venous, — 

 acquires a dark hue, and its capacity for heat is diminished; 

 consequently its temperature rises, — the heat which was pre- 

 viously latent, is, from the decrease of capacity, sufficient to 

 raise its temperature, and is evolved. In this mode, the loss of 

 heat which occurs from the inferior temperature in which we 

 live, is compensated. The fresh supply is taken in at the lungs, 

 and brought into use in the minute vessels. 



Of late, this theory has fallen into discredit. 



All experiments upon the capacities of bodies for heat are very 

 delicate and liable to error ; and the conclusions of Crawford on 

 this point have been denied by MM. Delaroche and Berard, 

 with respect to the gases, and by Dr. Davy, with respect to arte- 

 rial and venous blood.* 



Mr. Brodie cut off the communication between the brain and 

 lungs of animals, and continued respiration artificially.! The 

 usual chemical changes continued in the lungs upon the blood, 

 nevertheless the temperature of the animals diminished, and even 

 more rapidly than if the respiration had not been continued, owing, 



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* Philos. Trans. 1814; •<! •' f Philos. Trans. 1812. 



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