Final answer:
The specific experiment conducted by Southam to test his hypothesis about HeLa cells is not described in the student's question, which primarily details the importance and history of HeLa cells in medical research.
Step-by-step explanation:
The experiment to test Southam's hypothesis about HeLa cells was not explicitly described in the student's question. However, the information provided about HeLa cells outlines their significance in medical research and the fact that they were derived from Henrietta Lacks's cancer cells. This line of cells became instrumental in medical advances due to their ability to divide indefinitely in culture.
Leonard Hayflick's experiment, which is not clearly mentioned but may be what the student is referring to, involves the Hayflick limit that describes the number of times a normal human cell population can divide until cell division stops. Southam's specific experiment on HeLa cells is not detailed in the question and will require additional context to provide a precise experiment description.