MOVEMENTS.] PHYSIOLOGY, • 39 



being simple I have been all this while speaking of 

 one muscle only, the biceps in the arm. But there 

 are a multitude of muscles in the body besides the 

 biceps, as there are many bones besides those of the 

 arm, and many joints besides the elbow. But what I 

 have said of the one is in a general way true of all the 

 rest. The muscles have various forms, they pull upon 

 the bones in various ways, they work on levers of 

 various kinds. The joints differ much in the way in 

 which they work. All manner of movements are pro- 

 duced by muscles pulling sometimes with and some- 

 times against each other. But you will find when you 

 come to examine them that all the movements of 

 which your body is capable depend at bottom on this — 

 that certain muscular fibres, in obedience to 

 a something reaching them through their 

 nerves, contract, shorten, and grow thick, 

 and so pull their one end towards the other, 

 and that to do this they must be continually 

 ^ supplied with pure blood. 



Moreover, what I have said of the relations of 

 muscle to blood is also true of all other parts of the 

 body. Just as the muscle cannot work without a due 

 supply of blood, so also the brain and the spinal cord 

 and the nerves have even a more pressing need of 

 pure blood. The weakness and faintness which we 

 feel from want of food is quite as much a weak- 

 ness of the brain and of the nerves as of the muscles, 

 — perhaps rather more so. And other parts of the 

 body of which we shall ha^'e to speak later on need 

 blood too. L^-i^t^^ '^ -^ 



The whole history of our daily life is shortly this. 

 The food we eat becomes blood, the blood is carried 



