PART II 



THE POWERS OF LIFE 

 CHAPTER VIII 



VITALITY 



I. The Task of Physiology — 2. The Seat of Life — 3. The Energy of 

 Life — 4. Cells, the Elements of Life — 5. The Machinery of 

 Life — 6. Protoplasm — J. The Chemical Elements of Life — 8. 

 Growth — 9. Origin of Life 



i. The Task of Physiology. — So far we have been 

 considering the ways of living creatures, as they live and 

 move, feed and grow, love and fight ; as they build their 

 homes and tend their young. We shall now turn to 

 the inner mysteries, and seek, so far as we may, to fathom 

 the wisdom Of the hidden parts. We shall describe the 

 machinery — the means by which the forces of life cause 

 those movements by which we recognise their presence. 



This study is called physiology ; and the plan of our 

 sketch of present knowledge will be as follows : We shall 

 first try to realise what we mean by life ; we shall then 

 limit ourselves to the consideration of certain kinds of life, 

 and attempt to make plain in what parts of all living 

 creatures are the forces of life most active. Having done 

 this, we shall describe the life processes of the simplest 

 creatures, and then those of the higher animals. 



It is not easy to say clearly what we mean by life ; but 

 we recognise as one of its characteristics the power of 

 movement. 



