298 THE ANIMAL AS A PRIME MOVER. 



The vital machine, on the other hand, has purposes and performs 

 offices of essentially different kinds. It must not only transform the 

 latent energies of the supplies received by it into useful external work, 

 but all its work being directed toward the sustenance and preservation 

 of the contained soul, as its principal and always essential purpose, all 

 its operations being automatic or self-directed, all its powers of trans- 

 formation of energy are demanded for the production, by transforma- 

 tion, presumably, of (1) the vital forces and energies ; (2) the physical 

 energies demanded in constructing, rebuilding, and operating the ani- 

 mal frame; (3) the external work required to furnish the body supplies, 

 to protect it from decay or injury, and to minister to the physical 

 wants and ethical requirements of the personality of which it is at 

 once the home and the vehicle. 



This curious prime mover is thus an apparatus which, from familiar 

 sources of energy, transfers and transforms, for its own purposes and 

 applications, a variety of energies, performing a variety of work in 

 various realms. The nature and composition of the sources of latent 

 energy, always chemical compounds capable of oxidation, are well 

 known; the character and method of many of the internal as well as 

 of the external expenditures of energy are equally well understood; 

 but there are a variety and considerable number of internal operations, 

 involving transformations of energy, the nature and method of which 

 are entirely beyond observation by any process of experimentation yet 

 devised. 



''Food" is taken into the body, enters into solution with the peptic 

 fluids, elaborated from previously supplied nutriment, is absorbed into 

 the circulation, and disappears from our sight and reach; heat, carbon- 

 dioxide, vapor of water, various salts, and a considerable proportion of 

 unutilized nutriment are rejected from the system, and work is per- 

 formed as the product of transformed energies and in large amount, 

 both within the machine and upon external bodies. A chain of energy 

 transformations is in continuous operation, of which we see the two 

 ends, so far as the vital machine is concerned, but of which we only 

 get occasional glimpses between the extremities, and some of the links 

 of which are, as yet, undiscovered and unknown. It is certain that the 

 series of changes, material and kinetic, involves familiar methods of 

 transformation, and it is hardly less certain that singular and probably 

 wonderful and unknown processes of energy development and transfor- 

 mation are concealed within this miracle among machines. 



Possibly a study of the present state of scientific research relative to 

 this machine may give at least some idea of the importance and com- 

 plexity of the problems here placed before the man of science and the 

 engineer, if not give a clew to their final solution. 



The source of power in the animal machine is invariably the stored 

 chemical energy of vegetation, the potential energy of the hydrocarbons 

 and other compounds contained in all plants, and capable of uniting 



