Despite worrying results, demand for tuberculin overwhelms the Charité. Behring's diphtheria cure is put to the test. Ida meets Tischendorf's father.

Koch fails in one aspect of his life, but succeeds in another. Ehrlich faces a betrayal and increasing anti-Semitism. Ida rethinks her future plans.

Nurse Therese falls ill. Koch tests tuberculin on humans, starting with himself. Behring reaches a breakthrough in his work on a diphtheria cure.

Spinola repays Behring for saving a life. Ida is urged to pursue an ambitious dream. Koch receives two visitors: a Tokyo doctor and the new emperor.

Koch reveals big news at the congress while Ehrlich struggles to find a doctor to deliver his wife's breech baby. Tischendorf and Ida's romance blooms.

Pathologist Virchow tries to uphold his liberal values in a time of upcoming nationalism. Doctor Koch continues his work on battling the rampant tuberculosis. Von Behring tries, in vain at first, to join his lab while Jewish Doctor Ehrlich is welcomed for his work on colorizing cells. Ms. Lenze recovers after an appendicitis but has to work off the fees for her treatment by working as a nurse.