stem at a distal end thereof the sample retainer is a cage having a cage wall 112 defining a region within which is captured a biological sample in use the biological sample which may include any of the material identified above but is not limited to those materials is placed directly into the sample cage the sample is inserted into the cage by means of removing an end plug 108 to access the cage the plug 108 can be refitted in this case with a resilient snap fit to retain the sample perforations 114 provide fluid communication into the cage but prevent the sample from leaving the cage in use the sample holder is fitted into the cassette 50 as shown by the position of sample holder 100 u2032 in fig1 the cassette has receiving chambers 52 for convenience three chambers 52 are shown but it is equally likely that just one two or more chambers could be employed in this position the sealing cap 104 engages a complementary surface of the chamber to hermetically seal the receiving chamber 52 also the cap acts to support the stem and cage and suspend the same in the chamber to provide correct positioning of the cage in the chamber the cassette 50 is assembled with an.