424 THE CANADIAN NATURALIST* [J)eC. 



their action, wliich 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 elementary 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 andneurine, substances the synthesis of which was but 

 yesterday an impossibility.^** 



In studying the phenomena of living beings, it is important 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, converts the 

 actual energy of the sunlight into potential energy 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 energy, which 

 at any time, may become actual as force. This food the animal 

 now appropriates ; he brings it in contact with oxygen, and the 

 potential energy becomes actual ; he cuts the string, the weight 

 falls, and what was just now only attraction, has become actual 

 force ; this force he uses for his own purposes, and hands back the 

 oxidized matter, the fallen weight, to the plant to be again de- 

 oxidized, to be again raised. The plant then is to be regarded as 

 a machine for converting sunlight into potential energy : the 

 animal, a machine for setting the potential energy free as actual, 

 and economizing it. The force which the plant stores up is 

 undeniably physical; must not the force which the animal sets 

 free by its conversion, he intimately correlated to it? 



But approaching our question still more closely, let us, in 

 illustration of the vital forces of the animal economy, choose three 

 forms of its manifestation in which to seek for the evidences of 



