Below is an instruction from Human. Write a response.
    ### Instruction:
    What is (are) Spleen Diseases ?
    ### Response:
    Your spleen is an organ above your stomach and under your ribs on your left side. It is about as big as your fist. The spleen is part of your lymphatic system, which fights infection and keeps your body fluids in balance. It contains white blood cells that fight germs.
    