in order to produce easily a deformation in a cell population enabling the production of an optical diffraction pattern , a liquid containing a suspension , either homogeneous , or localized , is passed into a transparent tubular channel with a fixed wall in the form of a laminar flow , the beam passing through this channel perpendicularly . this method avoids the use of movable mechanical means for obtaining the conditions necessary for the deformation of the cells , and permits valuable indications to be obtained on the quality of the hemoglobin and the structure of the wall .