The 1860s were a period of rapid scientific progress, but an enormous number of foundational discoveries still lay ahead. Germs, electrons, radioactivity, genetics, viruses, blood types, other galaxies, and even entire groups of chemical elements were all unknown or unrecognized during that decade. Here’s a look at the most significant things the world had not yet discovered.
Germs as the Cause of Disease
In the 1860s, most people and many physicians still believed that disease came from “bad air,” foul smells, or even evil spirits. The idea that tiny organisms could invade the body and make you sick was not yet established. Louis Pasteur was doing early work on microorganisms during this period, but it took until the final decades of the 19th century for Robert Koch to conclusively prove that a specific germ could cause a specific disease. Before that proof arrived, surgeons operated with bare, unwashed hands, and hospitals were breeding grounds for infection. Until the 20th century, losing a child to disease was tragically common, in large part because no one understood what was actually causing illness.
Viruses
Even after bacteria were identified as disease agents, an entirely separate category of pathogen remained invisible. Viruses were not discovered until 1892, when a Russian scientist named Dmitri Ivanovsky showed that the agent causing tobacco mosaic disease could pass through a filter fine enough to trap all known bacteria. Something smaller than any bacterium was causing infection. In 1898, the Dutch microbiologist Martinus Beijerinck confirmed the finding and coined the term “virus” to describe this new kind of infectious agent. He demonstrated that unlike bacteria, it could move through gel, behaving more like a dissolved substance than a solid particle. The entire concept of a virus simply did not exist in the 1860s.
Genetics and Heredity
Gregor Mendel actually published his famous experiments on pea plants in 1866, right in the middle of the decade. But here’s the twist: nobody noticed. His paper was sent to 120 recipients, and Mendel ordered just 40 reprints. The work was completely ignored by the scientific community. Even Charles Darwin, who was actively puzzling over how traits passed from parent to offspring, almost certainly never encountered Mendel’s results.
It wasn’t until 1900, more than three decades later, that three different scientists independently rediscovered Mendel’s principles. Only then did the world begin to understand that inheritance follows predictable patterns governed by discrete units (what we now call genes). Throughout the 1860s and for decades after, heredity remained a mystery.
The Electron and Atomic Structure
In the 1860s, scientists knew atoms existed, but they had no idea what was inside them. The electron, the first subatomic particle ever identified, wasn’t discovered until 1897. That year, J.J. Thomson at Cambridge showed that cathode rays could be deflected by an electric field, revealing them to be streams of tiny, negatively charged particles far smaller than any atom. Thomson proposed that atoms were spheres of positive charge with these small negative particles embedded throughout, like raisins in a pudding. Before this discovery, the internal structure of matter was a complete blank.
Radioactivity
The 1860s had no concept of radioactivity. The phenomenon was discovered in 1896 by Henri Becquerel, who found that uranium emitted penetrating rays similar to the X-rays that Wilhelm Röntgen had just discovered the year before. This opened the door to understanding that atoms are not stable, indivisible spheres but can release energy spontaneously. Marie and Pierre Curie would soon expand on Becquerel’s work, discovering radium and polonium. None of this was even imaginable in the 1860s.
An Entire Group of Chemical Elements
Dmitri Mendeleev published his first periodic table in 1869, organizing the known elements by their properties. But he had no idea that an entire group was missing. The noble gases, including helium, neon, argon, krypton, and xenon, were all discovered between 1894 and 1898 by William Ramsay. These five elements added a completely new column to the periodic table and fundamentally changed how scientists understood the way electrons hold atoms together. In the 1860s, not a single one of these gases had been identified.
Blood Types
Blood transfusions had been attempted for centuries before the 1860s, but they were essentially a gamble. Sometimes patients survived, sometimes they died, and no one understood why. The answer came in 1901, when Karl Landsteiner at the University of Vienna discovered the ABO blood group system. He showed that human blood comes in distinct types, and mixing incompatible types triggers a fatal immune reaction. This single discovery made safe transfusions possible for the first time. Throughout the 1860s, doctors had no way to predict whether a transfusion would save a patient or kill them.
Insulin and the Treatment of Diabetes
Diabetes was a known condition in the 1860s, but it was essentially a death sentence, particularly for what we now call type 1 diabetes. There was no understanding of the hormone that regulates blood sugar. Insulin was not extracted until 1921, when Frederick Banting and Charles Best isolated it from animal pancreases. In 1922, a diabetic teenager named Leonard Thompson became the first person to receive an insulin injection, transforming the disease from fatal to manageable. For the entire 1860s and more than half a century beyond, there was simply no treatment.
Neurons and How the Brain Works
The 1860s brain was essentially a black box. Scientists knew it controlled the body, but they didn’t understand its basic building blocks. The technique that first revealed individual nerve cells wasn’t developed until 1873, when Camillo Golgi created a staining method that made single neurons visible under a microscope. Santiago Ramón y Cajal then used this method in the 1890s to systematically map brain tissue, arguing that the nervous system is made of individual cells that communicate across tiny gaps rather than forming one continuous network. Charles Sherrington later named those gaps “synapses.” The electron microscope finally proved Cajal right in the 1950s. In the 1860s, none of this architecture was known.
Other Galaxies
People in the 1860s looked up at the night sky and assumed the Milky Way was the entire universe. Every star, every fuzzy patch of light, was thought to belong to our single galaxy. That belief held until 1923, when Edwin Hubble photographed the Andromeda nebula in detail and found a pulsating star deep in one of its spiral arms. By calculating its distance, he proved that Andromeda was far beyond the Milky Way, making it an entirely separate galaxy. The universe went from containing one galaxy to billions in a single discovery. For the people of the 1860s, the cosmos was unimaginably smaller than we now know it to be.
Plate Tectonics and Moving Continents
The idea that continents move was not even proposed until the early 20th century, and it was widely rejected for decades after that. The theory of plate tectonics, explaining that Earth’s rigid outer shell is broken into massive plates that slowly shift, collide, and pull apart, was not accepted by geologists until the late 1960s. That makes it one of the most recent major scientific revolutions. In the 1860s, the continents were assumed to have been fixed in place since the formation of the Earth. No one suspected that the ground beneath their feet was in constant, imperceptibly slow motion.
Practical Electric Lighting
While early experiments with electric arc lamps date back to 1835, no one in the 1860s had a practical electric light bulb. Scientists spent roughly 40 years tinkering with filaments and bulb atmospheres before Thomas Edison’s team produced a bulb in October 1879 that could last 14.5 hours using a carbonized cotton thread filament. Edison then went further, building the first system for distributing electricity from a central generator through wires, demonstrated in London in 1882. In the 1860s, the world ran on gas lamps, candles, and oil. The idea of flipping a switch to light a room was still two decades away.