OS) S t 



attractions. No overpowering or supernatural agency 

 comes in to complicate their action, which is modified 

 only by the action of the others. Vitality, therefore, is 

 the sum of the energies of a living body, both potential 

 and actual. 



Moreover, the important fact must be fully recognized 

 that in living beings we have to do with no new elemen- 

 tary forms of matter. Precisely the same atoms which 

 build up the inorganic fabric, compose the organic. In 

 the early days of chemistry, indeed, it was supposed 

 that the complicated molecules which life produced 

 were beyond the reach of simple chemical law. But as 

 more and more complex molecules have been, one after 

 another, produced, chemistry has become re-assured, and 

 now doubts not her ability to produce them all. A few 

 years hence, and she will doubtless give us quinine and 

 protagon, as she now gives us coumarin and neurine, 

 substances the synthesis of which was but yesterday an 

 impossibility. 20 



In studying the phenomena of living beings, it is im- 

 portant also to bear in mind the different and at the 

 same time the coordinate purposes subserved by the 

 two great kingdoms of nature. The food of the plant 

 is matter whose energy is all expended ; it is a fallen 

 weight. But the plant-organism receives it, exposes it 

 to the sun's ray, and, in a way yet mysterious to us, con- 

 verts the actual energy of the sunlight into potential en- 

 ergy within it. The fallen weight is thus raised, and 

 energy is stored up in substances which now are alone 

 competent to become the food of the animal. This food 

 is not such because any new atoms have been added to 

 it ; it is food because it contains within it potential en- 



