Doctor's Review: Medicine on the Move

January 17, 2022
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Sperm spotter

How an unlikely, untrained scientist unlocked biology's best-kept secret

These days, most giggling fifth-graders have a good inkling about sperm, eggs and what happens when the two get together. But while it's hard to imagine a time when people didn't know how babies are made, it wasn't until the 17th century that science caught up with instinct. Indeed, the first piece of the puzzle was put into place by a self-taught scientist with no formal medical education -- a man who was more comfortable around a bolt of fabric than a bell jar.

It's more amazing still that the secret got out at all, even once the necessary tools were in place and sperm was discovered. With all the rigours and rigamarole imposed upon science by religion in days past (and present!), the fact that Antony van Leeuwenhoek's findings were so readily accepted and disseminated to both the scientific and lay communities was nothing short of a miracle.


Above all else, Antony van Leeuwenhoek was a curious fellow. Born in Delft, Holland in 1632 into a nice middle-class family -- his father's people were basket-weavers, his mother's were beer-makers -- he too appeared destined for the quiet life of a tradesman. At the age of 16, he left school for an apprenticeship in a linen shop in Amsterdam, where he learned to determine the thread counts of cloth by examining the textiles beneath a magnifying glass. A few years later, he returned home to Delft, opened up his own fabric store and set to work. The most extraordinary thing about young Leeuwenhoek at the time was his supposed friendship with Jan Vermeer, even serving as the trustee of his estate when the master painter died in 1675. But the clothsman was destined for far more than one famous friendship.

During his early years as a draper, his interest in magnification grew. After reading a well-known book on the subject -- Micrographia (1665), written by the brilliant English scientist, Robert Hooke -- he became aware of a tiny world people were just beginning to explore. Hooke's book was a beautifully illustrated work. Among other things, it presented elaborate engravings of microscopes, plant life and insects, including, most famously, the eye of a fly. Incidentally, it was also Hooke who first observed and coined the word "cell," since the firm boundaries of these basic biological building blocks reminded him of the cells monks lived in. Van Leeuwenhoek was fascinated.

He worked hard at improving the lenses he used in his trade, hoping to put them to use examining scientific swabs rather than swaths of cloth. To that end, Leeuwenhoek took the looking glass to the next level, artfully crafting and grinding small lenses, increasing their curvatures and optical quality so that, eventually, he was able to achieve an impressive magnification of 270X. Considering the standard draper's magnifying glass had a power of about 3X, this was quite an improvement! Although credit for inventing the first microscope usually goes to the late-16th-century Dutch father-and-son optometrist team of Hans and Zacharias Janssen, Van Leeuwenhoek's device was the first practical microscope in that it was functional and reliable.


The mysteries of the world in miniature unfolded before Van Leeuwenhoek's eyes. He gave up the cloth trade to devote himself to his scientific pursuits. With his microscope -- whose single, convex lens was focused using two screws -- he went on to discover many great things. His natural curiosity led him to study everything beneath his lenses and he even collaborated with a scientific illustrator to record all of his observations in greater detail. Eager to share his discoveries with the world, he wrote to London's Royal Society. He sent his first letter in 1673.

To the Society's great credit, they were interested in his work, despite the fact that Van Leeuwenhoek only spoke Dutch, had no relevant education to speak of and was unknown to everyone in the scientific and medical communities. For 50 years, the Royal Society translated his correspondence and reports on everything he saw through his microscope, from microorganisms and other biological matter to inorganic samples of all kinds, and published them. The French Academy of Sciences also picked up his work and soon, the scientific world was abuzz.

An incredible series of scientific firsts soon followed. The first item to be described and subsequently published was his account of a bee stinger. With no shortage of sample sources to inspire him -- from fossils to his own feces -- Van Leeuwenhoek worked furiously. He wrote eloquently in 1674 of the world of wonder contained in a single drop of lake water, and described the amazing "animacules" -- the first mention of microorganisms in the literature -- found in plaque scraped off the teeth of old men. Bacteria, blood cells, capillary circulation, single-celled creatures, algae, yeast, microscopic worms... Van Leeuwenhoek found them all. Most famously, however -- and potentially the most scandalous -- was what the Dutch diviner discovered in his own ejaculate in 1677.


Like so many great scientists of the past, Van Leeuwenhoek enjoyed experimenting on himself -- and in this case, who could blame him? And so, the man who is kindly known as the Father of Microscopy (despite the fact that the microscope was actually invented several decades before he was born) became the first to spot these important little swimmers live and in action. More importantly still, he proposed the fertilization theory of reproduction: a complete about-face from the commonly held wisdom at the time, which stated that life basically just sort of happened if the conditions were just right.

Apparently, the countless little tadpole-like creatures beneath his lens bemused Van Leeuwenhoek. Ever the diplomat, he recorded what he saw and presented his discovery to the Royal Society with the following disclaimer:

"What I investigate is only what, without sinfully defiling myself, remains as a residue after conjugal coitus. If your Lordship should consider that these observations may disgust or scandalize, regard them as private and to publish or destroy them as your Lordship thinks fit."

Despite the fact that some naysayers wrote off these newfound spermatozoa as nothing more than bacteria, the Society bigwigs saw the value in Van Leeuwenhoek's output, and published the news, unsure exactly what sort of fallout to expect... and from whom.


Though the church's position on such matters at the time was firmly entrenched in the so-called "spontaneous generation of life" camp, Van Leeuwenhoek -- a religious man himself -- skirted the issue by proclaiming sperm just another one of God's miracles. The church accepted this compromise and the scientific community was happy to leave the theory behind, too, adopting instead the concept of omne vivum ex ovo -- that every living thing comes from another living thing. As the microscopic wonders of nature became clearer thanks to Van Leeuwenhoek, other scientists began to follow in his footsteps; before long, the very nature of scientific understanding had changed.

Van Leeuwenhoek was elected a fellow to the Royal Society in 1680, after a team of delegates sent to Delft to double-check his observational skills reported that the draper and his lenses really were all they were cracked up to be. He went on to demonstrate the wonders of microscopy to many famous figures, including the Tsar of Russia and the Queen of England.

In addition to his scientific pursuits and successes, he remained an enthusiastic craftsman of magnifiers throughout his life. In this regard, Van Leeuwenhoek was unequalled and extremely prolific, producing an estimated 500 lenses and 400 microscopes. Many of his devices were made of precious metals, which may be why very few, if any, original Van Leeuwenhoek microscopes exist to this day. After his death in 1723, his family members and other owners sold many of them for the value of the copper, silver and gold with which they were made.

It was the little Dutch man who could who opened the scientific community's eyes to so many of nature's miracles in miniature. As the centuries rolled on, bigger, better and brighter microscopes came along -- some built on Van Leeuwenhoek's design; others designed from scratch -- which shed more light into who we are, revealing the awesome anatomical details of our own form, as well as those of the natural world we inhabit. Today, electron microscopes have the power to magnify up to two million times and are capable of showing us far more than just sperm and cells, stripping us down to our very DNA.

Impressive, to be sure, but remember -- all it took to spy the sperm that started it all was an untrained tradesman and his 270X microscope.

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