302 BIOLOGY 



out of starches, can convert one proteid into another, and can 

 make new living protoplasm if fed with lifeless proteids; all of 

 these are constructive processes. Whatever energy is needed 

 for this work must be obtained by breaking down part of the 

 food, so that the result is a reduction of the total amount of 

 organic materials. In their constructive work, animals are not 

 only unable to make starches and sugars, but they are unable 

 to make proteids. Since they require these as materials out 

 of which to manufacture muscles, nerves, glands, 'etc., it fol- 

 lows that they are dependent upon plants, not only for starches 

 but also for proteids, which the plants manufacture and which 

 the animals utilize. 



From this outline of the transformation of energy it is evi- 

 dent that living organisms, both animals and plants, are in 

 a strict sense machines. That living beings possess special 

 powers shown by no other kind of mechanism, and therefore 

 belong in a category by themselves, is very evident; but so far 

 as concerns the problem of energy they are machines. Vital 

 energy is only the energy of sunlight transformed into various 

 types within the mechanism of the living machine. Since 

 coal is simply an accumulation of the remains of plant life of 

 past ages, we now see the source of its energy. It contains 

 the stored sunlight of the past. 



