referring now to fig1 and 2 , the measuring device for the deformation of red blood cells illustrated includes a measuring channel denoted as a whole by 1 and having a port or channel proper whose passage cross - section , shown in fig2 is that of a flattened rectangle of width equal to 1 cm and height equal to 100μ . the channel is formed from an upper glass plate 3 of rectangular shape and a lower thicker glass plate 4 also of rectangular shape , provided at its front and rear ends with an inlet passage 5 and an outlet passage 6 . a fluid - tight peripheral seal 7 is interposed between the two glass plates 3 , 4 , so as to form lateral edges of the passage cross - section . as can be seen in fig1 the channel 1 , whose length is about 4 cm is arranged vertically so as to be traversed by the beam 8 of a laser 9 , said beam 8 being directed perpendicularly to the assembly of glass plates 3 , 4 to be recovered on a screen 10 or other device enabling analysis of the diffraction image formed . the discharge passage 6 of the channel 1 is connected by a tube 11 to a discharge receiver 12 . at its side , the inlet passage 5 is connected to an inlet tube 13 ending at a mixing chamber 14 at which terminates a pump 15 , for instance a piston pump constructed in the form of a syringe and provided with actuating means ( not shown ), said pump 15 enabling injection with a regular flow rate , or red blood cells , into the chamber 14 . the chamber 14 is on the other hand connected to a mixing chamber 16 at which end the outlets of two pumps 18 19 , also shown in the form of syringes , the pistons 20 of said pumps being also driven by suitable drive means . the liquids contained in the pumps 18 and 19 and which are mixed in the desired proportions in the chamber 16 , form by mixing in said chamber the liquid intended to comprise the cell suspension . this liquid is , for example a dextran solution having the viscosity of 10 cp and the desired tonicity . due to the use of the two pumps 18 , 19 and of the mixing chamber 16 , it is possible to vary , as desired , the viscosity , the tonicity or the partial pressures or again other parameters of the medium , and this so as to obtain either a medium of constant composition during the whole measurement or a medium of gradually variable composition . in operation , it is understood therefore that the device enables the establishment through the channel proper 2 of a laminar flow of a homogeneous suspension of red blood cells in the liquid of composition provided in advance . the movement of this suspension through the channel produces a diffraction image recovered on the screen 10 . this diffraction image , which has circular concentric rings when the liquid is at rest , becomes elongated and takes on a characteristic configuration when the liquid flows with a laminar movement through the channel 2 , the configuration of the image being characteristic of the deformation undergone by the suspended red blood corpusles . the flow rate of the stream traversing the channel 2 , and consequently the amplitude of the flow speeds , is determined by the amount of the pressure upstream provided by the different pumps . it is also possible to provide regulating means for this flow rate in order to obtain a perfectly constant flow rate which can be established at adjustable desired values . the various characteristics of the suspension , namely the composition of the liquid , its partial pressures , its tonicity , as well as the density of the red blood cells in the liquid , are easily defined by the technician skilled in the art and have no need to be modified with respect to the values used for measurements in equipment of the prior art such as that described in the aforesaid french patent . instead of being of flattened rectangular shape , the cross - section of the channel could also be square , for example a square of 150μ side , or even circular , for example of diameter comprised between 25 and 100μ , the length of the channel being such that taking into account the possible turbulence caused by the arrangement of liquid inlets and outlets , the zone traversed by the light beam is traversed by a flow of laminar type . in general , a length of some centimeters is sufficient . in this second embodiment , the channel is formed inside a glass tube 22 of internal diameter 150μ . this glass tube is connected to a flared portion 23 of funnel shape whose diameter decreases progressively toward the tube 22 and whose end of largest diameter is connected to a cylindrical chamber 24 . inside this chamber 24 , and concentrically with the common axis of the assembly , is arranged an annular needle , that is to say , a needle having a cylindrical outer peripheral wall 26 and an inner peripheral wall 25 defining between then a narrow annular space 27 open through its front end , closed at its rear end and receiving in the vicinity of the latter an inflow of red blood cells 28 in concentrated suspension in a suitable liquid medium . the inner wall 25 is extended outside of the chamber 24 at its rear end , and is connected to a liquid inlet tube . the same liquid is also introduced into the chamber 24 through a passage 29 , the flow rates of liquid through the inner space 30 of the wall 25 and through the peripheral space 31 of the chamber 24 being such that any notable turbulence does not tend to be produced at the level of the front end of the needle 24 , 25 so as to create in the vicinity of the front end of the needle a practically laminar flow zone , this laminar flow continuing inside the tube 22 . for the measurement , there is therefore established in the space 30 and in the space 31 a flow rate of liquid devoid of red blood cells so as to tend to cause in the frustoconic portion 23 and the tube 22 a flow of laminar nature and there is established simultaneously a flow of red blood cells through the annular space 27 which then forms in the liquid an annular suspension 32 of red blood cells spaced both from the axis of the tube 22 and from the wall of the latter . as is seen notably in fig4 the red blood cells remain concentrated in this annular portion 32 of the cross - section in which the speed gradient is large . in this way there is obtained on the screen a diffraction image which is still more distinct and precise enabling measurements of very great accuracy . of course , the injection of red blood corpuscles into a suitable portion of the passage cross - section of the channel can be effected along different geometries . thus , in the example of fig1 it would be possible , instead of injecting the red blood cells into a mixing chamber upstream of the channel 2 so as to obtain a homogeneous suspension , to inject on the contrary the red blood cells inside a chamber 1 , into the channel , so the cells become disposed along a flat configuration of little thickness arranged for example at mid - distance between the inner wall of the upper glass plate 3 and the central portion of the channels 2 . it is self - evident that the technician skilled in the art could vary , not only the geometry of the cross - section of the channel , but also the dimensions of the latter as well as the value of the suspension flow rate passing through the channel . the corresponding values can be obtained by simple experiments , it being understood that the thickness of the channel , that is to say the distance traversed by the beam inside the channel , must vary as a function of the state of dilution that it is desired to obtain , as is otherwise known . the distance traversed by the beam in the solution actually containing the erythrocytes is at least equal to 25μ . the upper value of this distance is preferably limited to 150μ , this being principally to avoid flow rates which are too high , a dilution which is too great , as well as the difficulties of maintaining a laminar flow in too large a passage cross - section , but it is self - evident that these values , indicated for practical reasons , are not critical from the theoretical point of view . the dilution is preferably such that about 80 to 90 % of the cross - section of the light beam is intercepted by the particles . lastly , the embodiments of the invention which have been described in detail are simply preferred embodiments and it is self - evident that the method can be put into practice by other means . thus , it was observable , surprisingly , that it was possible to practise the method according to the invention in devices such as those of the aforementioned french patent , provided that the rotary walls of the latter were immobilized and that the liquid was forced to flow with the desired flow rate through the device . the channel can be curvilinear as well as rectilinear . although the invention has been described with regard to a particular embodiment , it is understood that it is in no way limited thereto and that it is possible to introduce various modifications of form therein without however departing from either its scope , or its spirit .