WORK THE MUSCLES 1<M 



The Maintenance and Regulation of Temperature 



In the first stage of muscular contraction, in which the 

 potential energy is converted into tension, no loss in the form of 

 heat is to be detected. That is, the whole of the potential energy 

 lost appears in the form of mechanical tension, which can perform 

 external work. If no external work is done, on the other hand, 

 this energy becomes heat, and there is always heat produced in the 

 restitution phase, since only a part of the energy obtained by com- 

 bustion is stored as potential energy in the muscle system. We see, 

 therefore, how the temperature of warm-blooded animals is kept up 

 by muscular activity. The advantage of having a raised tempera- 

 ture is that the numerous processes, physical and chemical, go on 

 at a faster rate, the former being less affected than the latter. It is 

 even a debateable question whether the raised temperature in fever 

 is not beneficial in the destruction and elimination of the bacteria 

 and the poisons they produce. 



The heat produced in muscular activity serves, then, to main- 

 tain the raised temperature in warm-blooded animals. But in 

 muscular exercise too much is produced, and we become too hot. 

 How do we get rid of the excess? The most effective way is the 

 familiar one of sweating, since the evaporation of water requires a 

 large amount of heat energy, which is drawn from the skin and 

 indirectly from the blood. Evaporation of water from the lungs 

 must also be added. A less effective way is by widening the blood 

 vessels in the skin and allowing more loss by radiation, and by 

 heating the air by conduction. 



In hot weather we make use of yet another means, that is, by 

 reducing muscular activity as far as possible. 



In cold weather we diminish loss by narrowing the blood 

 vessels of the skin, and we increase production by greater muscular 

 activity. One form of the latter is " shivering " an automatic 

 method of keeping warm. A hibernating mammal, on waking up, 

 raises his temperature in this way with rapidity. 



Thus, the most effective way of lowering the temperature is by 

 sweating ; of raising it is by muscular activity. 



Since the source of our energy is food and we need less heat 

 energy in hot weather because we lose less to the surroundings it 

 is clear that less food is required in the summer. 



There are, as we see, several factors involved in the regulation 

 of our temperature, so that the necessity of a co-ordinating centre 

 is obvious. Such a centre has been found in a part of the brain, 

 situated between the highest intellectual parts and the more 

 automatic parts. This centre is so arranged as to be sensitive to 

 the temperature of the blood passing through it. If this tempera- 



