Microbe Hunters

Paul Henry de Kruif’s medical science book, Microbe Hunters (1926), explores the truth behind the earliest microbial discoveries and explains where vaccinations come from. The book is still widely respected and read today. De Kruif was a bestselling nonfiction writer whose work inspired many aspiring physicians, scientists, and technicians to join the field. Best-known for Microbe Hunters, he is also remembered for greatly assisting Sinclair Lewis with his 1925 Pulitzer-Prize-winning novel, Arrowsmith.

In Microbe Hunters, de Kruif tells the stories of the first scientists to work on microbes and bacteria. We know bacteria and viruses cause illnesses, but this knowledge came from somewhere. Every scientific discovery begins with a pioneer; de Kruif encourages us to remember the scientists who paved the way for the vaccines we take for granted today.

Each of Microbe Hunters' twelve chapters focuses on the microbial discovery of a single scientist. The earliest “microbe hunters” found these tiny living organisms and studied their behavior, whereas later scientists developed this knowledge, learning how to interact with the microbes directly. Given the book’s age, readers should be aware that science has progressed since its publication, but it remains a useful study tool.



Microbe Hunters begins with the first hunter, Antony Leeuwenhoek. Although Leeuwenhoek was the first scientist to discover microbes, he has largely been forgotten by the modern world. Leeuwenhoek lived in Holland during the seventeenth century. Few people trusted science yet, and people were very superstitious. Leeuwenhoek grew up illiterate and he never attended university. However, de Kruif explains that because of his ignorance, Leeuwenhoek made his most important discoveries.

Since Leeuwenhoek couldn’t read, others didn’t influence him. He relied wholly on his own senses and ingenuity. He taught himself how to make a microscope, discovering strange shapes moving around inside a droplet of water. We now call these living things microbes. Paving the way for microbial science, Leeuwenhoek is known as the “Father of Microbiology.”

Leeuwenhoek is significant for the way he stumbled upon ground-breaking knowledge. De Kruif reminds readers that many significant discoveries happen entirely by accident. Lazzaro Spallanzani, who followed Leeuwenhoek, wasn’t a typical scientist, either. He made his discoveries by trial and error. He loved to know how things worked, and he set out to learn everything he could about microbes. Through various, haphazard experiments, Spallanzani eventually proved that microbes reproduce. This is how they spread and multiply.



Microbial study fell silent for many years after Spallanzani’s discovery. Scientists accepted that microbes exist, but they didn’t understand how dangerous microbes can be. No one realized that microbes cause disease and that they are responsible for mass epidemics. Not until the 1830s did scientists learn about the link between microbes and sickness.

In the 1830s, a boy called Louis Pasteur questioned why townsfolk died after a dog bite. His family told him that demons killed people through mad dogs. They told Pasteur to stop asking strange questions and accept the will of God. Pasteur, however, couldn’t stop thinking about these dog bites. He dedicated his life to proving that microbes somehow caused illness.

Another scientist, however, declared he could prove that microbes caused sickness. To some extent, he stole the limelight from Pasteur. This scientist, Robert Koch, astounded Germany with these accusations, but his claims made Pasteur more determined than ever to complete his life’s work. Pasteur eventually proved that infecting animals with small, weak volumes of microbes didn’t kill them. Instead, the animals recovered from the infection. Pasteur paved the way for the first vaccinations. He finally proved that dog bites made people sick because the bites transferred lethal microbes to the human body.



De Kruif admits that the eighteenth and nineteenth centuries were terrible times to be an animal. Scientists, now convinced that they could defeat dangerous microbes, experimented on countless animals. They killed everything from guinea pigs to chickens, and they injured many more. Animal welfare didn’t exist in this early scientific world. Readers should be aware that de Kruif describes animal experiments in some detail.

Scientists eventually realized that they could harness vaccines to treat disease outbreaks. For example, they learned how to stop the spread of yellow fever by finally ceasing animal experiments and testing the vaccines on humans instead. Microbe Hunters explores the brave sacrifices made by scientists and volunteers alike, all in the name of microbiology. We should remember that scientists often endanger themselves to save the rest of us.

Microbe Hunters tells the personal stories behind these scientists, reminding us that scientists are, above all, human. We shouldn’t remember these pioneers simply for their discoveries—we should remember them for their humanity first. The book ends on an optimistic note, with the hope that scientists will eventually unlock every secret of the microbiological world.