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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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