Final answer:
To address internal bleeding, one should immediately call for emergency medical assistance. Elevating the legs may help, but only if instructed by emergency services, while tourniquets and giving fluids are not recommended in this situation. In critical emergencies requiring blood transfusion without known blood type, type O negative blood is utilized.
Step-by-step explanation:
When a casualty is showing signs of internal bleeding, the correct course of action is to call for emergency medical assistance immediately. Internal bleeding can be life-threatening and requires prompt medical evaluation and treatment. Elevating the legs can help maintain blood flow to vital organs, but this should only be done if directed by emergency services. A tourniquet is not appropriate for internal bleeding; it is used for severe extremity bleeding that cannot be controlled by direct pressure. Giving fluids is not recommended unless directed by a healthcare professional, as it could potentially worsen the situation depending on the internal injury.
Regarding blood transfusions in an emergency, when a patient's blood type is unknown and there is no time for testing, type O negative blood is used because it is the universal donor type and is most likely to be compatible with all patients.