What precautions should be taken when filling gaps in a 100-year-old floor to ensure its structural integrity and longevity?

When filling gaps in a 100-year-old floor, it is important to first assess the overall condition of the floor and consult with a professional to determine the best approach. Precautions that should be taken include using appropriate materials that are compatible with the existing floor, ensuring proper support and reinforcement of the floor structure, and allowing for expansion and contraction of the wood. It is also important to address any underlying issues that may have caused the gaps in the first place to prevent future damage.