24)2 ANIMAL HEAT. 



Warm-blooded animals are continually eating; birds, whose tem- 

 perature is the highest, incessantly, if they can obtain food; where- 

 as the cold-blooded eat little and seldom. Some make a meal only 

 once in three or more months; Dr. Stevens saw a large rattle- 

 snake, plump, active, and venomous, which was said not to have 

 tasted food for nine months. u 



The temperature of parts falls if not maintained by a constant 

 stream of blood from the lungs through the aorta and its rami- 

 fications, and is, caeteris paribus, in exact proportion to this 

 supply. When parts shrink, and are pale, they are cold from 

 want of blood: when they do not shrink, or they are even full, 

 turgid, and purple, they are cold from the want of changed blood. 

 Still for a time respiration may not be quick and yet the tempera- 

 ture high, as in the yellow fever of the West Indies v : combustion 

 may go on rapidly in the extreme vessels of a part or the whole of 

 the body, for a limited period, disproportionately to the removal 

 of the product, the carbonic acid, in the lungs, and the supply 

 of oxygen for the combustion. On the other hand, general or local 

 temperature may be low though respiration be rapid, for it may 

 carry off carbonic acid and supply oxygen to little purpose, if the 

 circulation in the extreme vessels languishes. 



Whether the theory be correct or not, the production of 

 animal heat must be as evidently a chemical process, as changes 

 of temperature among inanimate bodies ; yet some ascribe it to 

 nervous energy. I cannot imagine nervous energy to cause heat 

 any more than to cause chemical affinity. As it may bring sub- 

 stances into proximity which have an affinity for each other, and 

 thus produce their union, so it may effect those changes which are, 

 according to physical laws, accompanied by changes of tempera- 

 ture ; but caloric in the body must, I apprehend, like affinity, 

 follow the same laws, and no others, as out of the body. This, 

 however, does not prevent animal temperature from deserving 

 the epithet vital, because it is regulated by the vital powers of 

 the system, although through the instrumentality of chemical 

 changes. If the high temperature of an inflamed part is 

 owing to the increased momentum, the increased sum of the 

 quantity and velocity of its blood, yet this increased momentum 

 is produced by the vital powers. 



Sir B. Brodie removed the brain of animals, and continued 



u 1. c. p. 35. T Dr. Stevens, 1. c. p. 38. 



