In 1890, Koch announced the discovery of tuberculin, a substance derived from tubercle bacilli, which he thought was capable of arresting bacterial development in-vitro and in animals. This news gave rise to tremendous hope throughout the world, which was soon replaced by disillusionment when the product turned out to be an ineffective therapeutic agent. In this paper Koch provided his definitive expression of "Koch's Postulates."
The second paper described “Koch’s phenomenon”, and tuberculin skin test. Koch showed that tuberculin injected intradermally would elicit a severe local inflammatory reaction in tuberculous patients. This was the first diagnostic skin test. Abbreviated English translation of second paper in Bibel, Milestones of immunology (1988).