INTRODUCTION.] PHYSIOLOGY. 



making it go on. Not until you have wound it up 

 will it go on again as it did before. And every time 

 you want it to run you must wind it up afresh. 

 Living animals move again and again, and yet need 

 no winding up, for they are always winding themselves 

 up. Indeed, as we go on in our studies we shall 

 come to look upon our own bodies and those of all 

 animals as pieces of delicate ntiachinery with all 

 manner of springs, which are always running down 

 but always winding themselves up again. 



3. You are warm ; beautifully warm, even on 

 the coldest winter day, if you have been running hard ; 

 very warm if you are well wrapped up with cloth- 

 ing, which, as you say, keeps the cold out, but really 

 keeps the warmth in. The bed you go to at night 

 may be cold, but it is warm when you leave it in the 

 morning. Your body is as good as a fire, warming 

 itself and everything near it. 



The bird too is v^arm, so is the dog and the horse, 

 and every four-footed beast you know. Some animals 

 however, such as reptiles, frogs, fish, snails, insects, and 

 the like do not seem warm when you touch them. 

 Yet really they are always a little warm, and some 

 times they get quite warm. If you were to put a 

 thermometer into a hive of bees when they are busy 

 you would find that they are very warm indeed. All 

 animals are more or less warm as long as they are 

 alive, some of them, such as birds and four-footed 

 beasts, being very warm. But only so long as they 

 are alive; after death they quickly become cold. 

 When you find a bird lying on the grass quite 

 still, not stirring when it is touched, to make quite 

 sure of its being dead you feel it. If it is quite 



B 2 



