Color ultrasound smear liquid is generally gel, clinical gel varieties. Because color ultrasound ultrasound can not pass through the gas, but the gas is everywhere, the gel can make the ultrasound probe and the body surface completely attached, to avoid the gas to produce too much interference, can be effective, clear observation of the specific situation of the tissue in the abdominal cavity. When a patient uses less gel or does not apply gel during the ultrasound examination, the gas will enter between the ultrasound probe and the tissues, and it will not be possible to see the specific conditions of the organs.