the call of nature

:  to speak in a loud distinct voice so as to be heard at a distance :  shout

:  to make a request or demand

:  to utter a characteristic note or cry

:  an act of calling with the voice :  shout

:  an imitation of the cry of a bird or other animal made to attract it

:  an instrument used for calling

:  the inherent character or basic constitution (see constitution 2) of a person or thing :  essence

:  disposition, temperament

:  a creative and controlling force in the universe