Dr. Richard L. Riley, whose work with guinea pigs as a Johns Hopkins Hospital researcher in the 1950s proved that particles the size of a mote of dust could transmit tuberculosis, died of a stroke Monday at a hospital in Athol, Mass. He was 90 and had been living in Petersham in central Massachusetts.
Dr. Riley - who wrote most of his roughly 120 scientific papers on the 1928 Remington typewriter he got as a high school graduation present - was equally well known for his work explaining the mechanisms that allow the body to exchange oxygen and carbon dioxide.
"His work absolutely laid the foundation for modern understanding of this problem," said Dr. Solbert Permutt, professor at the Johns Hopkins Asthma and Allergy Center who began working with Dr. Riley in 1956. "Most of our principles come from Riley."
Although he retired in 1978, Dr. Riley consulted on various projects until his death. His work from the 1950s and 1960s is still widely discussed, as scientists try to understand more about drug-resistant tuberculosis - and even how inhalation anthrax can be prevented.
Last week, researchers gathered at the Centers for Disease Control and Prevention in Atlanta to discuss a federally funded project to duplicate Dr. Riley's tuberculosis experiments in Witbank, South Africa. Using his model, the South Africa project will try to determine how long people remain contagious from tuberculosis, and will also examine the effectiveness of using ultraviolet light to eradicate tuberculosis germs.
That technique, which Dr. Riley pioneered at Hopkins, is now part of a national project to prevent the spread of TB at homeless shelters. The project was started by Dr. Edward Nardell, a Harvard Medical School professor who said he began working with Dr. Riley in 1983 after hearing him give a talk on ultraviolet light.
A native of North Plainfield, N.J., Dr. Riley graduated from Harvard University in 1933 and Harvard Medical School in 1937.
During World War II naval service in Pensacola, Fla., he became interested in the problem of how pilots could go higher and still breathe properly and launched his research on the physiology of respiration.
After the war, he went to the Columbia School of Medicine in New York but was recruited in 1950 by Johns Hopkins. Six years later, at a time when tuberculosis was a major national killer, he and a team that included his former Harvard mentor, launched a four-year experiment that became crucial to preventing the disease.
Taking over a six-room ward at the top of the Veterans Administration Hospital in Baltimore, Dr. Riley's team set up 150 guinea pigs in cages, and connected air ducts from the cages to the rooms of tuberculosis patients. In a paper published this year, Dr. Riley described the strain the project put on the hospital: "A damn nuisance for everybody," he wrote. "And this went on for years."
The results proved that even the tiniest particles, called droplet nuclei, coughed up by infected people could transmit the disease. "Up until then, we had sort of ignored the little tiny droplets that evaporate almost immediately," concentrating instead on large particles that fell to the ground and mixed into dust, said Dr. George R. Comstock, professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health.
From 1960 to 1977, Dr. Riley was chairman of the Department of Environmental Medicine at Hopkins, and in 1970, the National Tuberculosis and Respiratory Disease Association awarded him its highest honor, the Edward Livingston Trudeau Medal.
"He had this great capacity to be interested in the work of other people, and to encourage them and help them," said Dr. Permutt. "He was turned on by the kind of quantitative thinking that goes with putting equations together. If it ended in an algebraic expression, he wasn't turned on. But graphs! Graphs were things that just blew his mind."
His son, Richard C. Riley of Ithaca, N.Y., said Dr. Riley was also an accomplished pianist who had considered a career in music and played his favorite Bach pieces until he died. He also wrote poems to commemorate every family occasion and was an expert tennis player.
"More than anything, he was a graceful man," his son said. "Physically graceful and intellectually graceful. Opinionated as hell, but a very warm person."
Dr. Riley's wife of 51 years, the former Mary Catesby Jones, died in 1999.
Surviving, in addition to his son, are his wife of two years, the former Barbara Sleigh Ellis; two daughters, Mary Louisa Riley of Shanghai, China, and Susan Holt Riley of Petersham; and two granddaughters.
Plans for a memorial service were incomplete. The family suggested donations to Petersham Unitarian Church, Petersham, Mass. 01366.