The colours seen especially in dissected specimens provide a wealth of information for interpreting the structure. Both spirit and formaldehyde preserved specimens suffer from rapid loss of colour, some being bleached white in only a few weeks. The techniques below have been developed within the medical community to prevent this loss. Before using these preservative fluids on animal specimens, the thorax and abdomen should be opened taking care not to cut any major blood vessels thus retaining as much of the blood as possible.