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Alfred Kahl only spent a decade in the world of the microcosmos, but in that time he discovered more ciliates than anyone else ever has!

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When you’ve been on a journey through the  microcosmos, there are some names that start   to feel pretty familiar. Antonie van Leeuwenhoek comes up pretty often, as befits a microscopist   whose delightful descriptions of the bacteria  and protozoans essentially birthed a whole field   of research.

Then you’ve got Müller, and your  Ehrenberg, your Dujardin—names that endure because   of the microbial knowledge they are attached to. Alfred Detlef Fritz Kahl   has one of those names. The more you look into  the literature to identify ciliates, the more   his name comes up.

And yet, he’s probably one  of the more mysterious figures of microbiology.  We know that he was born in 1877, in a town  north of Hamburg, Germany. And we also know   that he was a high school teacher who taught  English, French, and natural history. But any   other details of his personal life are  obscure except that he had a daughter   Lucia who attended a series of lectures about  protozoans at the Tropical Institute of Hamburg.  And we know this because in  one of his works, Kahl wrote,   “The very interesting literature and preparations  my daughter Lucia brought home fascinated me, as a dedicated biologist, and created the desire to study this field more deeply.” So Kahl did what people who develop a  curiosity for the microbial world do:   he got some water from nearby and he put  it under a microscope.

The year was 1924,   and Kahl dedicated himself to studying the  literature and mastering the microscope.   Using a brightfield microscope, he would use a  micropipette to take an individual specimen and   watch it at low magnification with no cover slip.  At this point, he could gather information about   the organism’s overall shape and movement, and  then he would apply the cover slip, elevating it   with little dots of Vaseline underneath the  corners to keep from crushing the ciliate.   With a needle, he then very gently pushed down the  edges until the coverslip was applying just enough   pressure to render the organism immobile, but not  so much that the slide would squish it to death.   The process is delicate, and it  takes time to master, but it works.  Kahl estimated that it took him about 9  months to feel confident in his drawing   and identification skills. And  from there, he went all out.   His first monograph was published in  1926, when he was 49. His last publication   came around 1935.

And in that period of time,  he published 21 papers that totaled around   1800 pages of descriptions and illustrations  of around 700 new species of ciliates.  Yes, 700.  For reference, in 1974, the microbiologist John  O. Corliss described what he saw as—up until   that point— three ages of ciliate classification.  The first period lasted roughly from 1880-1930,   and he named it the age of discovery. Scientists  during that period discovered about 500 species.  In the course of a decade,  Kahl more than doubled that.  Of course, Kahl was benefiting from advancements  in microscopy and experimental techniques, and he   was building off an available base of literature.  And yet his accomplishment still stands as   uniquely his—he was largely working  alone, and yet through careful work,   and dedication, he probably discovered  more ciliates than anyone else ever has.  Kahl’s contributions extended beyond just  uncovering new species.

The second age of ciliate   discovery, which lasted between 1930 and 1950, was  marked not by a need to just uncover new species,   but to understand how to better group them. By  the end of just the 1930s, there were around   3,000 known ciliates to classify, leading  to the creation of new taxa and genera   that some have called Kahlian classification  because of the labels he introduced into it.  Though of course like many microbial taxonomy  efforts, these labels would undergo massive   changes in later eras of research. The third  era that Corliss described lasted between 1950   and 1970, and this era would apply the  advanced techniques of those days to better   the relationships between the roughly 6,000  species known at the time.

And of course,   those relationships are still being revised  and updated with the new techniques of today.  Kahl’s classification system may not have  lasted, but maybe that’s part of its value.   Our understanding of microbes is marked by  so many stories of how we have attempted to   classify and reclassify and reclassify again. And  given how many species we have yet to encounter,   it is a task that will likely never end. During his lifetime, his work invited its share of   criticism.

Some took issue with his methods, while  others disagreed with the definitions he used to   distinguish species. But while Kahl acknowledged  the feedback, his careful and thorough work   would produce descriptions that still endure  and inform our understanding of ciliates.  But his work seemed to come to an abrupt  end in 1935 for reasons that are not known.   Some have speculated that he was frustrated with  both the criticisms from academic scientists,   and the challenges of getting his work  published. There is a manuscript from 1943,   submitted to the journal Mikrokosmos  aimed towards amateur microscopists like   Kahl.

But whether there was meant to be more  would become irrelevant: Kahl died in 1946,   and those who have looked into these questions  have found neither an obituary nor a grave.  There are mysteries both microbial and  human to this story, and if Kahl helped   us solve some of the former, he left us with  more of the latter. Just as we know little   about the beginning of his life, we know little  about the end of it as well. It’s really just   that decade of work that seems to have lasted.

But oh how it has lasted. Alfred Kahl’s texts   have gone on to become immensely  important to those who study ciliates,   filled with drawings that help those  like James, our master of microscopes,   who are trying to figure out what they see under  their microscopes. The tools may have changed,   the ways we share information has evolved, but the  delight and the curiosity—that remains unchanged.  Thank you for coming on this journey with us as  we explore the unseen world that surrounds us.

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