Abstract: The present invention relates to a membrane suitable for use as the support for one or more test reagents for testing a material applied to the membrane, which membrane is characterized in that it is initially an open pored porous material and in that at least part of the length the pores therein are blinded so that cell wall fragments from the material applied to the membrane are substantially prevented from passage through the membrane. Preferably, the pores are totally blinded by a gelatin matix containing one or more reagents which react with a fluid applied to one surface of the membrane to give a color which can be observed from a second surface of the membrane.