Simplify the following text for a Grade 11 native English-speaking person.
Original: With the widespread use of the microscope in the 18th century , it was discovered that the ` cancer poison ' spread from the primary tumor through the lymph nodes to other sites ( `` metastasis '' ) .
Simplified: With the microscope , it was discovered that the ` cancer poison ' spread from the one tumor through the lymph nodes to other sites ( `` metastasis '' ) .