1944 · Oswald T. Avery; Colin M. MacLeod; Maclyn McCarty
Studies on the Chemical Nature of the Substance Inducing Transformation of Pneumococcal Types
What this work is
The 1944 paper by Avery, MacLeod, and McCarty on the substance that changes one type of pneumococcus into another. They extracted a stringy liquid from killed Type III bacteria and showed it turned rough cells into smooth Type III cells, a change their descendants kept. Protein-digesting enzymes left it working, preparations that broke down DNA stopped it, and they concluded the substance is DNA.
Then and now
Avery, MacLeod, and McCarty showed that a stringy extract from dead bacteria changed living ones, and that enzymes which thin fish-sperm extract stopped it. Biology teaches this as the proof that genes are made of DNA. The paper showed a liquid changing colonies, not a gene, and nobody has seen one.
Verdict
UNSCIENTIFIC
The work only partly follows the scientific method inside its paradigm, and the paradigm itself does not pass. The worse layer decides. The verdict is unscientific.
1·This work · inside the paradigm
MIXED
Partly follows the scientific method within Genomics / DNA Model.
2·Paradigm · Genomics / DNA Model
UNSCIENTIFIC
Fails the tests. The worse layer decides.
How the verdict is decided
The verdict grades both layers: the paradigm this work assumes, and how the work was carried out inside it. Both must be scientific for the whole thing to be scientific. A clean method inside an unscientific paradigm is unscientific. An unscientific method inside a better paradigm is unscientific. A split on either layer is mixed. The worse layer decides.
1·This work
Did this work test its claim with methods that are independent, falsifiable, and non-circular?
MIXED
This study claims that DNA is the chemical substance that transforms one type of pneumococcus bacterium into another, and that the change is inherited by the descendants. The tests split.
Independently Verifiable
Fail
The glossy transformed colonies are visible to anyone, but the liquid only becomes 'DNA' at the step where sugar color tests and nitrogen-phosphorus ratios are read through the nucleic acid chemistry.
Falsifiable
Pass
Protein-digesting enzymes destroying the transforming power, or the viscosity-destroying enzyme leaving it intact, would have killed the claim in the titration tubes, and nothing in the design could hide either result.
Non-Circular
Pass
The activity was scored by colony growth on blood plates and the chemistry was calibrated on fish-sperm fractions from another laboratory, so no instrument here was built from the conclusion it was used to prove.
Why
The changed colonies are visible, but the liquid becomes DNA only through color tests and element ratios read by nucleic acid chemistry. Protein enzymes stopping the change, or the DNA-thinning enzyme leaving it intact, would have killed the claim in the tubes. Activity was scored by colonies on plates and the chemistry was set on fish-sperm fractions from another lab, so no tool here was built from the conclusion.
2·Paradigm · Genomics / DNA Model
Does the framework this work assumes pass the three tests?
UNSCIENTIFIC
Independently Verifiable
Fail
The framework's central entity is a name attached to color tests, element ratios, and viscosity readings; no one has seen DNA.
Falsifiable
Fail
Inside this framework a failed transfer is read as enzyme degradation or trace protein contamination, so no experiment the field runs can count against DNA carrying the specificity.
Non-Circular
Fail
The enzyme used to prove the point was defined by its action on fractions the same chemistry had already called nucleic acid, and every later DNA test descends from that naming.
Why
The DNA model began with this kind of work: a viscous fraction that changed how bacteria grew. The fraction and its effect are real. The model's move was to name the fraction from its chemistry, then, over the following decades, to promote that named substance into a code said to specify every trait. Every tool the field now uses to find DNA was built after that naming, from sequences the model itself assembled. In this paper, the enzyme that destroyed the transforming principle was itself defined by what it did to other fractions already called nucleic acid by the same chemistry. And when a transfer fails in this framework, the answer is a degraded sample, trace protein, or bad technique. The name never carries the risk. A stranger can watch the colonies change. The substance doing the changing, as the field describes it, has only ever been the model reading its own instruments.
From the work
This difference in the character of growth makes it possible by inspection alone to distinguish tentatively between positive and negative results.
Analysis of these results shows that irrespective of the presence of phosphatase or esterase only those preparations shown to contain an enzyme capable of depolymerizing authentic samples of desoxyribonucleic acid were found to inactivate the transforming principle.
If it is ultimately proved beyond reasonable doubt that the transforming activity of the material described is actually an inherent property of the nucleic acid, one must still account on a chemical basis for the biological specificity of its action.