Possible Clues:

• Examination of tissue from a living body
• Test on living tissue
• Test sample by ring-fencing lion heart ¿ it says so at end of letter
• Examination of tissues or liquids from a living body
• On tops of built-in ovens, perhaps saucepans with unknown quantity of a sample that needs to be examined
• Diagnostic tissue exam
• Medical test involving the extraction of sample tissue or cells
• Tissue analysis
• Examination of tissues cut from living body