The word “Animal” derives from the Latin (anima, animus) name for the vital principle called “Soul” which is a life principle associated with functions like breathing, or the principle called animation. Breathing is a vital function as it is associated with the “Power” of self-nutrition. The power of self-nutrition is the originating power, the possession of which leads us to speak of things as living, and non-living. Nutrition is a vital power as the action is not a mechanical performance. Nutrition is a function associated with a purpose and it is guided to achieve a future end and it involves the choice or selection of specific means to attain the desired goal of its action.