I want to know the answer to the following question:
What animal byproduct was imported to Plymouth in the 19th century?
All the background I'm provided with is that "Aside from the dockyard in the town of Devonport, industries in Plymouth such as the gasworks, the railways and tramways and a number of small chemical works had begun to develop in the 19th century, continuing into the 20th century.". Is that enough to answer the question?