Avery, Macleod, and McCarty

Who Were They? 

     Oswald Avery was born on October 21, 1877 in Halifax, Nova Scotia, Canada. He attended Colgate College and then Colgate University. Afterward, he entered the College of Physicians and Surgeons in New York and got his medical degree in 1904. He then moved to the Hogland Lab in Brooklyn in 1907 to work on the bacteriology of yogurt but then got interested in tuberculosis. Later, he joined the Rockefeller Institute of Medical Research to participate in a pneumonia research program.

    Maclyn Mccarty was born on June 9, 1911 in South Bend, Indiana. In 1929, he attended Stanford University for pre-med training and entered medical school at John Hopkins University in 1933. In 1940, he accepted a position to work with William Tillet at New York University. Tillet arranged for McCarty to join Avery’s lab at the Rockefeller Research Institute to pursue his interest in bacteriological research.

    Colin Macleod was was born on January 28, 1909 in Port Hastings, Nova Scotia, Canada. He finished primary school at age 15 and once he was old enough, he went to McGill University where he completed his medical research. He received his medical degree at age 23. In 1934, he began medical research in New York as a part of the Pneumonia Service (directed by Rufus Cole and O.T. Avery) in the Rockefeller Institute Hospital, which is where the Avery-Macleod-McCarty experiment began.


    After hearing about Griffith’s experiments on bacterial transformation, Avery was skeptical and decided to replicate the experiments. However, Avery wanted to see if this transformation could occur inside of a test tube, or in vitro, instead of in mice. He hypothesized that each pneumococcus contains the necessary enzymes to produce capsules of all major types and that each capsule is characterized by a different polysaccharide. He thought that if nonpathogenic bacteria of each type had lost the ability to produce any of the capsules, the ability could be reestablished through transformation. In addition, he stated that the transforming factor was similar to a gene that could be transferred from dead cells to live cells.


    To test their hypothesis, Avery, Macleod, and McCarty removed the lipids and carbohydrates from a solution of heat-killed pathogenic (type IIS) pneumococci. Proteins, RNA, and DNA remained. Then, they subject the solution to treatments of enzymes to destroy either the proteins (by adding proteinase), RNA (by adding ribonuclease), or DNA (by adding deoxyribonuclease). Finally, they added a small portion of each sample to a culture containing live nonpathogenic (type IIR) bacteria, observing whether or not transformation had occurred by testing for the presence of virulent type IIS pneumococci.


    In the two test tubes where the proteins and RNA were destroyed using enzyme treatments, transformation occurred and type S cells appear after adding R cells. In the test tube where DNA was removed and R cells were added, no transformation occurred and no S cells appeared.



    Since transformation could not occur if DNA wasn’t present, DNA must of been the transforming factor. This is also confirmed that DNA contains hereditary material.