Koch's postulates in relation to the work of Jacob Henle and Edwin Klebs.

Among the essential elements of a theory of disease is the set of criteria that must be satisfied to establish that some specific factor is the cause of a particular disease. For example, in the germ theory various nonequivalent criteria have been proposed for establishing that specific micro-organisms cause particular diseases.' Perhaps the most famous criteria are the conditions known as Koch's postulates. The postulates are invariably mentioned even in superficial discussions of Robert Koch's work. However, different authors state the postulates differently,2 and many authors provide no evidence that they have read Koch; often the only justification for stating the postulates in a particular way is a superficial secondary work.3 There is also disagreement about whether or not Koch adopted the postulates from his predecessors. Some commentators, assuming that Koch derived the postulates from Jacob Henle, refer to the postulates as the Henle-Koch postulates4 or even as the Henle postulates.5 Others deny that Henle significantly influenced Koch's thinking about causal criteria.6 Given that the postulates have been so influential, it is remarkable that there have been no serious attempts to resolve these issues. This essay will first determine how Koch stated and used the postulates in some of his early papers. We will then examine the research tradition from which Koch seems to have derived the postulates, and argue that Edwin Klebs was a more important