Marvels of Modern Medicine: Invention of Microscope and Eradication of Smallpox

FROM THE LECTURE SERIES: An Introduction to Infectious Diseases

By Professor Barry C. Fox, M.D., University of Wisconsin

Over the years, scientists, physicians, and inventors have contributed greatly toward the development and progress of medicine. The various discoveries and inventions laid the foundations of modern medicine, including the use of the microscopes and the total eradication of smallpox. Let’s take a look.

Collage of images showing concept of medical science.
Over the ages, various inventions and discoveries have contributed toward the growth of modern medicine. (Image: Triff/Shutterstock)

The Microscope and Antonie van Leeuwenhoek

The 1600s saw one of the most important milestones in modern medicine—the development of the modern light microscope to identify specific germs. Till then, scientists tried combining lenses to attempt to increase magnification. However, they were difficult to build and could only enhance objects by 20 to 30 fold.

Antonie van Leeuwenhoek is best known for his pioneering work and contributions toward the development of microscopes. Considered to be the “Father of Microbiology”, van Leeuwenhoek started as an apprentice in a dry goods store where magnifying glasses were used to count threads in cloth to determine quality. He taught himself to grind and polish the lenses and continued to construct microscopes. Later, he used them to discover bacteria in 1674. He was the first to identify single-celled organisms, as well as muscle fibers and blood flows through capillaries.

Robert Hooke’s Contributions

Image of a vintage microscope.
The invention of the microscope was a major breakthrough in the field of microbiology. (Image: moomsabuy/Shutterstock)

Another scientist, Robert Hooke is designated as the “English Father of Microscopy” and is famous for his book, Micrographia, which contains marvelous copperplate engravings of his findings, including details of a fly’s eye.

He was the first to use the term cell to describe what he saw—looking at slices of cork through his microscope that was divided into individual spaces. He confirmed Leeuwenhoek’s discoveries and improved upon the microscope’s design. Both Antonie van Leeuwenhoek and Robert Hooke contributed much to the emerging field of Microbiology.

This is a transcript from the video series An Introduction to Infectious Diseases. Watch it now on The Great Courses Plus.


A historically important disease, whose death rate rivaled that of the Plague, is smallpox. The cause of smallpox is traced to the variola virus, which is thought to have evolved from animals in the central African rainforest thousands of years ago. The virus became established in humans in the Nile River Valley approximately 10,000 years ago. Evidence of smallpox was even found in mummified bodies of the Egyptian pharaohs that date back to 10,000 BC.

Later, the disease became widespread in Europe and Asia, killing almost half a million Europeans yearly at the turn of the 19th century, with over 80 percent of them being children.

Spread of Smallpox

Smallpox enters the body through infectious particles, contacting the mucous membranes, or via the respiratory system via inhalation of droplets. From its initial site of the invasion, it spreads locally to lymph nodes, then jumps into the bloodstream, where it can enter other major organs. The pox on the skin is the visual clue of the internal disease.

The colonization of the “New World” carried smallpox to the Americas, where it played a major role in the conquest of Mexico and Peru, as well as the European settlement of North America. Many of the indigenous Native American populations, whose immune systems had never been exposed to the virus, were unable to fight off the disease, resulting in their deaths.

Learn more about global travel, war, and natural disasters.

Fight against Smallpox

One of the true triumphs of modern medicine has been the eradication of smallpox. As late as the 20th century, there were millions of worldwide deaths from smallpox. The World Health Organization estimated that as recently as 1967, 15 million people contracted smallpox and 2 million died of it that year.

And, in order to reduce the risk of smallpox, an ingenious preventive inoculation called “variolation” was devised as early as the 10th century in Asia.

Variolation for Smallpox

Individuals were deliberately injected with smallpox by blowing dried smallpox scabs into the noses of the individuals. These individuals usually contracted a mild form of smallpox, leaving them immune. Only 1 to 2 percent of these patients died, compared to the 30 percent mortality for others dying from smallpox without the variolation prevention.

In 1700, this procedure was being widely used in India, Africa, and the Ottoman Empire, but smallpox was still a serious threat with no treatment. Therefore, developing a more scientific vaccination for prevention was a world healthcare priority.

Learn more about emerging and reemerging diseases.

Vaccine for Smallpox

Image showing people receiving smallpox vaccine in the 1800s.
The smallpox vaccine played a major role in eradicating the disease. (Image: Everett Collection/Shutterstock)

A more traditional type of smallpox immunization was developed in 1796 by the English physician Edward Jenner.

Jenner was unaware that smallpox was caused by a virus, but despite his unawareness, he discovered that immunity to smallpox could be conveyed by inoculating a person with material from a cowpox lesion, a poxvirus from the same family. He called the material “vaccine” from the root word “vacca”, which is Latin for “cow”. Therefore, the term “vaccination” was coined.

Learn more about STDs and other infections below the belt.

Modern Vaccine and Eradication of Smallpox

The vaccine now is no longer a cowpox derivative like Jenner’s. Instead, it is a live vaccine derived from a similar poxvirus—the vaccinia virus. The last case of smallpox in the U.S. was in 1949, but in 1967, the disease was still endemic in 31 countries.

Since the “incubation period” for smallpox is relatively long, 7 to 17 days, and quarantine can be effective in halting transmission, smallpox was a prime candidate for worldwide eradication. The WHO worked hard over the next ten years to eradicate the disease and the last naturally occurring smallpox case in the world was in Somalia in 1977. In 1980, the world was declared free of smallpox.

These eradication programs demonstrate how international collaboration and cooperation can have a significant worldly benefit.

Common Questions about Marvels of Modern Medicine

Q: Who is considered the “Father of Microbiology”?

Antonie van Leeuwenhoek, is considered the “Father of Microbiology”.

Q: How does smallpox enter the human body?

Smallpox enters the human body through infectious particles, contacting the mucous membranes, or via the respiratory system via inhalation of droplets.

Q: What did Edward Jenner find out about immunization against smallpox?

Edward Jenner discovered that immunity to smallpox could be conveyed by inoculating a person with material from a cowpox lesion, a poxvirus from the same family.