the disclosure herein describes a method and apparatus for the removal , by dialysis , of gases physically dissolved in the blood of a person , more particularly a diver or an aviator ; the blood is brought into contact , in an exchange cell , with a membrane permeable to gases only ; a liquid having high solubility for gases is circulated on the side of the membrane so that the gases dissolved in the blood are made to follow their chemical potential gradient across the membrane into the liquid .