'Spirit' Collections are diverse. They can be considered to include all collections of biological specimens which have been prepared by an initial fixation of the tissue, followed by subsequent mounting in a preservative fluid, in a closed vessel. The fixing agent and the preservative can be identical, though more commonly they are not: there may have been intermediate steps of washing or dehydration between fixation and mounting, or not. The material preserved may be animal, plant or fungal; it may have been hard or soft, coloured or colourless, hydrophilic or water-repellent. The vessel containing the specimen may be of glass or a variety of plastics - and may itself be of historic interest. A 'pot' may be anything from modern to a few hundred years old and its condition, whatever its age, may be anything from excellent to irredeemably putrid. However, a feature common to all spirit specimens is that they change with time and require surveillance and periodic maintenance for optimal preservation. What is considered here is the nature of normal tissue cohesion, the chemistry of fixation and preservation and the relation between the two, in the context of these, slow changes.