THE ANIMAL AS A PRIME MOVER. 299 



with oxygen to form carbonic acid, water, and salts capable of solution 

 in water. It is possible, but perhaps not probable, that other sub- 

 stances and energies forming constituents of these compounds may 

 exist, having eluded the investigating chemist and physicist; but this 

 is thought unlikely. We probably know precisely what enters the 

 animal prime motor, and what are the sources of all its energies. Food 

 and air are the two known elements of all its powers. It is also pos- 

 sible, but probably not the fact, that this machine may drink in from the 

 surrounding ether some portion of its energy in forms still undetected and 

 unsuspected. We are compelled, for the present, certainly, to assume 

 that all the energies developed and applied in the vital machine are 

 initially latent in vegetable matter, air, and water. This organic sub- 

 stance is derived by the carnivorous animals indirectly through the 

 other creatures, all of which live upon vegetation directly. The organic 

 forces of plant life derive all energy from the inorganic world of min- 

 erals and from the gases of the atmosphere by utilizing the primary 

 energy of solar rays in the chlorophyll with which every leaf is provided, 

 as the active agent in that transformation. The vital machine thus 

 ultimately derives all its energies from the sun. 



Food is the material in which are stored the substances supplied to 

 the vital machine as the reservoir of the potential energy from which 

 the required energies, in various active forms, may be derived, as 

 demanded, to perform the work of the body and the mind. It consists 

 of a mixture of edible and other matter, the former being that part 

 from which energy is derivable; the latter being indigestible and unas- 

 signable and only useful in promoting, by mechanical irritation, the 

 action of the digestive system. 



All foods contain : 



Water — required for solution of nutrients. 



Xutrients — protein, fats, carbohydrates. 



Innutrient matter. 



Protein consists of the albuminoids, and, in vegetable matter, the 

 amides, a less valuable portion of the food. The white of egg, the 

 fibrine of meat, and the gluten of wheat are illustrations of albuminoid 

 compositions. 



Fats, such as those of meat, and the greases of vegetation, the oils 

 of the animal and vegetable compounds extractable by ether consti- 

 tute the basis of construction of the fats of the body and of a part of 

 the nerve and brain substance. 



Carbohydrates are the starches and sugars of the vegetable. 



Salts are found in both animal and vegetable foods, and are in some 

 cases essential elements of the compositions making up the body, though 

 not, in the ordinary sense, digestible and nutrient. 



Mineral matters constitute, in the case of the vegetable foods, the 

 principal portion of the innutrient matter of food, and form the ash 

 when the plant is burned. In some cases these mineral matters serve 



