It would be superfluous to comment on Koch's influence in the
development of modern bacteriology and medicine. Yet no collection of his
essays has ever been published in English. My purpose in preparing this
collection has been to correct this deficiency.

As I began work on this collection, my intention was simply to bring
together several of Koch's most important and influential essays. But Koch
wrote some two hundred items on a wide range of topics. I soon realized
that sampling his best work in all these areas would produce a long volume
containing essays that would seem almost unrelated to one another. I
decided that a selection of related papers would best reflect the coherence
and interconnectedness of Koch's thought. Once that decision was made it
was relatively easy to focus on Koch's early bacteriological essays.
Originally, I had intended to include some of Koch's writings on such
purely technical topics as disinfection and the conservation of cultures;
Koch was a master technician and these aspects of his work were extremely
influential. However, virtually all of Koch's work was based on technical
innovations, and his purely technical papers have less inherent interest than
those in which his new methods were used to attack theoretical problems--
especially the preeminent theoretical problem of nineteenth century
medicine: disease causation. Thus, I decided against including any papers
that were exclusively elaborations of bacteriological techniques. It also
seemed to me that a good sample of Koch's work on the etiology of
bacterial diseases should include not only the initial presentation of his
ideas, but at least some of his tenacious and devastating responses to
critics. These are the considerations that guided me in selecting the ten
essays that I have included.

Koch's studies of anthrax, wound infections, tuberculosis, and cholera
are marvelous illustrations of experimental technique combined with
theoretical insight. Taken as a whole, these studies are probably Koch's
best work. Thus, while whole areas of Koch's research are not represented
in this collection, the essays that are included provide an excellent sample
of Koch's finest contributions.

In preparing these essays, I have given a great deal of attention to
tracing Koch's sources. I have checked almost all of Koch's footnotes
against the original publications; I have provided additional information
when Koch's references were incomplete; and I have inserted new notes in
many places where Koch alludes to earlier writers without himself giving
bibliographic details. My notes and my additions to Koch's notes are all
bracketed. Without special notice I have taken some of Koch's biblio-

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