In the summer of 1952, at Cold Spring Harbor on the north shore of Long Island, geneticist Alfred Hershey and research assistant Martha Chase placed bacteria infected with radioactively labelled viruses into a Waring kitchen blender and switched it on. The experiment did not prove that DNA contains every instruction used by every living system. It did provide some of the clearest evidence yet that DNA, rather than protein, was the genetic material entering a bacterial cell during infection.
Their paper appeared in the September 20, 1952 issue of The Journal of General Physiology. Seven months later, James Watson and Francis Crick published their model of DNA’s double-helical structure.
The question that would not die
DNA had been visible to science since 1869, when Swiss physician Friedrich Miescher isolated a phosphorus-rich substance from white blood cells collected from used hospital bandages. He called the material nuclein, but its biological purpose remained obscure for decades, as the National Human Genome Research Institute recounts in its history of the discovery.
The obstacle was partly chemical. DNA appeared to be assembled from only four repeating bases, while proteins were built from twenty amino acids capable of folding into an enormous range of shapes. To many researchers in the early twentieth century, protein looked complex enough to encode heredity, while DNA looked too repetitive.
That assumption became harder to defend after Oswald Avery, Colin MacLeod and Maclyn McCarty published their landmark pneumococcus experiments in 1944. They showed that DNA purified from one bacterial strain could produce a lasting hereditary change in another, identifying DNA as the “transforming principle,” as the National Human Genome Research Institute explains.
Not everyone accepted the conclusion immediately. Questions remained about whether another substance in the preparation might have caused the transformation, and the wider field wanted an experiment in which DNA and protein could be followed separately. Hershey and Chase found a way to do exactly that.
Why a virus was the perfect witness
Their experimental subject was bacteriophage T2, a virus that infects Escherichia coli. A T2 particle consists largely of a protein structure surrounding DNA, creating a comparatively simple system in which the two candidate genetic materials could be separated and tracked.
When a phage attaches to a bacterium, part of the virus enters the cell and redirects the bacterium’s machinery toward producing new phages. Whatever entered had to contain the information required for that process. Hershey and Chase therefore needed to determine whether the entering material was protein, DNA or some combination of the two.
Cold Spring Harbor had already become an important meeting ground for the researchers studying bacteriophages, including Max Delbrück, Salvador Luria and members of the informal phage group. Hershey’s work on viral genetics would eventually help earn him a share of the 1969 Nobel Prize in Physiology or Medicine with Delbrück and Luria.
The trick with radioactive atoms
Hershey and Chase needed labels that would allow them to follow viral protein and viral DNA independently. Their solution came from the elemental differences between the two materials.
Phage proteins contain sulfur-bearing amino acids, while the phosphate backbone of DNA contains phosphorus. T2 DNA contains no sulfur, so radioactive sulfur-35 could be used principally to mark the protein coat, while phosphorus-32 could mark the DNA.
The researchers grew one population of phages with sulfur-35 and another with phosphorus-32. The resulting viruses carried detectable radioactive signals associated with different components. Instead of trying to see the molecules directly, Hershey and Chase could follow where each radioactive label travelled.
They allowed the labelled phages to infect fresh cultures of E. coli. Once the viruses had attached and infection had begun, they reached for the blender.
Why a kitchen appliance worked
The blender was not a novelty added for dramatic effect. Its shearing force was strong enough to knock most of the attached phage material away from the exterior of the bacteria, while leaving the bacterial cells largely intact. Hershey and Chase tested the procedure carefully before relying on it.
They then used a centrifuge to separate the components. The heavier bacterial cells formed a pellet at the bottom of the tube, while much of the detached viral material remained in the liquid above, known as the supernatant.
If protein had entered the bacteria, a substantial amount of sulfur-35 should have travelled into the pellet. If DNA had entered, phosphorus-32 should have remained with the bacterial cells and later appeared in newly produced phages.
The primary paper reports that blending released about 75 percent of the phage-associated sulfur into the surrounding solution, compared with only about 15 percent of the phosphorus. It also found that progeny from phosphorus-labelled phages retained 30 percent or more of the parental phosphorus, while progeny from sulfur-labelled phages contained less than 1 percent of the parental sulfur, according to the paper’s record and abstract in Cold Spring Harbor Laboratory’s repository.
Most of the protein-associated label stayed outside the bacteria. Most of the DNA-associated label entered with the cells, and part of it appeared in the viral descendants. The experiment strongly indicated that DNA was carrying the hereditary information needed to produce more phages.
September 20, 1952
Hershey and Chase did not write their conclusion in the sweeping language later histories would use. Their paper stated that the bulk of the sulfur-containing protein had no further function after infection and that the DNA had some function inside the cell. It also warned that further chemical conclusions should not be drawn from the experiments.
That caution mattered because the separation was not perfect. Some sulfur remained with the bacterial fraction, and some phosphorus was released into the surrounding liquid. The authors had shown what happened to most of the labelled material, not accounted for every molecule.
Martha Chase was listed as the paper’s second author, not merely acknowledged as technical help. She had completed her undergraduate degree in 1950 and worked with Hershey at Cold Spring Harbor from 1950 until 1953, contributing directly to one of molecular biology’s defining experiments.
Contemporary summaries sometimes describe the result more absolutely than the original authors did. A WIRED anniversary account, for example, captures how the experiment came to be remembered as the moment DNA displaced protein as the accepted carrier of hereditary information.
What happened over the next seven months
The result arrived while James Watson and Francis Crick were trying to determine DNA’s three-dimensional structure at the Cavendish Laboratory in Cambridge. The growing evidence that DNA was the genetic material made the molecule’s structure one of the most consequential problems in biology.
Their model drew on several lines of evidence, including X-ray diffraction data produced by Rosalind Franklin, Maurice Wilkins and their colleagues at King’s College London. In April 1953, Watson and Crick published their short Nature paper proposing the double helix.
Watson later became a central figure at Cold Spring Harbor Laboratory, serving as its director and then in other leadership positions. He died in November 2025 at the age of 97, more than seven decades after the blender experiment helped focus molecular biology’s attention on DNA.
The long tail of the experiment
The Hershey-Chase experiment became one of the foundation stones of molecular biology, but it was not the beginning of the story and did not stand alone. Avery, MacLeod and McCarty had already produced compelling evidence in bacteria, while later work explained DNA’s structure, replication and relationship to proteins.
Marshall Nirenberg, Har Gobind Khorana, Robert Holley and other researchers deciphered the genetic code in the following decade. Restriction enzymes, recombinant DNA, polymerase chain reaction, automated sequencing and CRISPR all depended on a progressively deeper understanding of how genetic information is stored and used.
The Human Genome Project published an initial draft sequence in 2001 and completed its main reference sequence in April 2003. That international effort examined DNA on a scale Hershey and Chase could not have imagined, generating the first sequence of the human genome, as the National Human Genome Research Institute records.
What the radioactive tags could not prove
The experiment directly addressed T2 bacteriophages infecting bacteria. It did not prove that DNA is the hereditary material in every biological entity, since some viruses use RNA genomes, and it did not show that DNA acts without proteins or other cellular machinery.
It also could not exclude every possibility involving an unlabelled or sulfur-free protein component. Hershey and Chase explicitly acknowledged that limitation in their paper, even as their evidence made the protein-coat explanation increasingly difficult to sustain.
The experiment’s influence came from convergence. Its results agreed with the earlier bacterial transformation work, with observations of phage infection and with the expanding body of evidence placing DNA at the centre of heredity. The blender experiment did not create the DNA case by itself, but it made that case much harder to dismiss.
The blender that remained
The machine was a commercially available Waring kitchen blender rather than a custom-built scientific instrument. What made it historically important was not its sophistication, but the precision of the question Hershey and Chase designed it to answer.
The original blender is now preserved in the Cold Spring Harbor Laboratory Archives. It remains a physical reminder that a decisive experiment does not always require exotic machinery, provided the materials can be separated cleanly enough to make the result visible.
The phosphorus-32 and sulfur-35 used in 1952 had relatively short half-lives, so the radioactive atoms that marked the experiment have long since decayed. The blender remains, the paper remains, and so does the pattern the counters revealed: most of the protein stayed outside, while the DNA went in.
