[Robert Koch's unpublished and unfinished experiments on sheep-pox (author's transl)].

The archives of the Robert Koch Institute include a casket with preparations and handwritten notes by Robert Koch (Fig. 1). He made these preparations during his time as a rural doctor between October of 1878 and September of 1880. They refer to an outbreak of sheep-pox at Rackwitz, a place near his practice at Wollstein (Fig. 2). This work has not been published; we know of it from one of Robert Koch's private letters (11). To reconstruct his working scheme and reasoning, we consulted particularly his reports on rinderpest experiments which he began in 1896 (6). The preparations from this casket which had been stained with Bismarck brown (according to Weigert) date back to a period when Robert Koch developed the foundations of bacteriology and they are evidence of his preparedness to accept new operational procedures (1, 2, 3). Thus, we have to assume that these preparations were to serve as evidence of a bacteriological etiology of sheep-pox. A wrong conclusion as to associations between the superinfection present and etiology of the disease (7) was ruled out by maintaining his own postulate. Simultaneously with this preparation work, Robert Koch performed animal experiments (11). His experience from these studies was utilized later on in his rinderpest experiments (6). On account of his confrontation with viral disease - which had its starting point in his unpublished work on sheep-pox - Robert Koch stated his postulate to be valid in the same manner as if bacteriological etiology had been demonstrated (4,6). The importance of these preparations is also seen in the interpretation of viral tissue damage, i.e. increase of macrophages and plasma cells with subsequent necrosis (9) characteristic of vira infection (Figs. 3, 4).