Connections were made by twisting the wire together, soldering, and wrapping with tape. Since the hot and neutral were run separately, the wiring tends to be rather confusing. The hot wire tended to run from one fixture to the next. The wire, insulation and insulators tend to stand up very well. I've seen, for example, is in quite good condition.
Grounding is usually difficult to install.
No bushing on boxes either, so wiring changes need special attention to box entry. Sometimes the neutral isn't balanced very well between separately hot circuits, so it is sometimes possible to overload the neutral without exceeding the fusing on any circuit. In fact, it was probably a Good Thing. This is a very bad thing. Consult your inspector.