BUT STILL MORE RAPIDLY EXPENDED. 877 



lows.* Hence also it is, that men in health can 

 endure a temperature of 32 during moderate 

 exercise, with more comfort and safety, than one 

 of 50 while in a state of rest ; and that when 

 supplied with an abundance of food, they can 

 endure the most intense degrees of cold, so much 

 better than during abstinence, as observed by 

 Franklin, Ross, and other travellers in the arctic 

 regions. 



We have also seen, that the vital activity of all 

 the organs, and the rapidity with which their 

 composition is renewed, are in proportion to the 

 amount of caloric that passes through them in a 

 given time, in combination with the arterial blood 

 by which they are nourished. But as it is a law 

 of nature that the cause of force is always expended 

 in producing motion, it will be found that the vital 

 heat of animals is wasted more rapidly during vio- 

 lent exercise, than it is obtained by respiration. 



* In accordance with the absurd theory of Bacon, Boyle, 

 Borelli, Boerhaave, Haller, and many others, that heat is the 

 effect of motion, friction, &c., it was maintained by Cullen, that 

 " animal heat is probably the effect of the motion of the blood, 

 because in dying animals, the heat grows less as the motion of the 

 blood grows less ; and when at death it ceases altogether, the 

 heat ceases also in a very short time." It is almost incredible, 

 that this sentence should have been written after Cullen was made 

 acquainted with the great discovery of Dr. Black. Nor is it less 

 remarkable, that Dr. C. Holland should have maintained that 

 exercise increases respiration and animal temperature, by causing 

 a less amount of blood than usual to pass through the lungs in a 

 given time. (Laws of Life.) 



