Luria

Luria, Alexander Romanovich, 1902-77, Soviet psychologist. Luria made advances in many areas, including cognitive psychology, the processes of learning and forgetting, and mental retardation. One of Luria's most important studies charted the way in which damage to specific areas of the brain affect behavior. His writings have been edited by M. Cole and S. Cole, The Making of Mind (tr. 1979).

Luria or Loria, Isaac ben Solomon, 1534-72, Jewish kabbalist, surnamed Ashkenazi, called Ari [lion] by his followers, b. Jerusalem. In his 20s he spent seven years in seclusion, intensely studying the kabbalah. He settled (c.1570) at Safed, Palestine, where he became the teacher and leader of a large circle of students who formed an important school of mysticism. Combining messianism with reinterpreted kabbalistic doctrines from an earlier period, Luria sought to understand the nature and connection between earthly redemption and cosmic restoration. Man's deeds, linked to the secret processes of creation and thus an integral part of the cosmic drama, work toward man's redemption by aiding in the restoration of the cosmos to its original state. It is the Jewish people, through their adherence to God's halakah, who will effect this restoration and thereby bring forth the Messiah as the consummate act of earthly redemption. Luria's philosophy has come down to us through the numerous works of his chief disciple, Hayim Vital.

Luria, Roger of: see Roger of Loria.

Luria, Salvador Edward, 1912-1991, American physician, b. Turin, Italy, M.D., Univ. of Turin, 1935. He conducted research and taught at the Institute of Radium in Paris (1938-40), Columbia (1940-42), Indiana Univ. (1943-50), and the Univ. of Illinois (1950-59) before joining the faculty at the Massachusetts Institute of Technology in 1959. In 1969 Luria, Max Delbrück, and Alfred Hershey were awarded the Nobel Prize in physiology or medicine for uncovering new information about the replication mechanism and genetic structure of viruses. Beginning in 1940, the researchers, working in parallel, became interested in using bacteriophages (viruses that infect bacteria) to study such fundamental life processes as self-replication and mutation. Luria conducted experiments that supported Delbrück's finding that radiation-induced genetic damage in bacteriophages could be repaired by gene exchange. The collective work of these three scientists contributed substantially to the discipline of virology and to the progress of molecular biology.

(born 1534, Jerusalem—died Aug. 5, 1572, Safed, Syria) Jewish mystic and founder of a school of Kabbala. He was brought up in Egypt, where he pursued rabbinic studies. He dedicated himself to the study of the Kabbala with messianic fervour, and in 1570 he journeyed to a centre of the movement in Galilee. He died two years later in an epidemic, having written little. The Lurianic Kabbala, a collection of Luria's doctrines recorded after his death by a pupil, had great influence on later Jewish mysticism and on Hasidism. It propounds a theory of the creation and later degeneration of the world and calls for restoration of the original harmony through ritual meditation and secret combinations of words.

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(born 1534, Jerusalem—died Aug. 5, 1572, Safed, Syria) Jewish mystic and founder of a school of Kabbala. He was brought up in Egypt, where he pursued rabbinic studies. He dedicated himself to the study of the Kabbala with messianic fervour, and in 1570 he journeyed to a centre of the movement in Galilee. He died two years later in an epidemic, having written little. The Lurianic Kabbala, a collection of Luria's doctrines recorded after his death by a pupil, had great influence on later Jewish mysticism and on Hasidism. It propounds a theory of the creation and later degeneration of the world and calls for restoration of the original harmony through ritual meditation and secret combinations of words.

Learn more about Luria, Isaac ben Solomon with a free trial on Britannica.com.

Luria-Delbrück experiment (1943) (also called the Fluctuation Test) demonstrates that in bacteria, genetic mutations arise in the absence of selection, rather than being a response to selection. Therefore, Darwin's theory of natural selection acting on random mutations applies to bacteria as well as to more complex organisms. Max Delbrück and Salvador Luria won the 1969 Nobel Prize in Physiology or Medicine in part for this work.

In their experiment, Luria and Delbrück inoculated a small number of bacteria into separate culture tubes. After a period of growth, they plated equal volumes of these separate cultures onto phage (virus) containing agar. If virus resistance in bacteria were caused by a spontaneous activation in bacteria--i.e., if resistance were not due to heritable genetic components, then each plate should contain roughly the same number of resistant colonies. This, however was not what Delbrück and Luria found. Instead, the number of resistant colonies on each plate varied drastically.

Luria and Delbrück proposed that these results could be explained by the occurrence of a constant rate of random mutations in each generation of bacteria growing in the initial culture tubes. Delbrück developed a sophisticated mathematical model based on this hypothesis that was entirely consistent with these results. The conclusion was that mutations in bacteria, as in other organisms, are random rather than directed.

The results of Luria and Delbrück were confirmed in more graphical, but less quantitative, way by Newcombe. Newcombe incubated bacteria in a Petri dish for a few hours, then replica plated it onto two new Petri dishes treated with phage. The first plate was left unspread, and the second plate was then respread, that is, bacterial cells were moved around allowing single cells in some colony to form their own new colonies. If colonies contained resistant bacterial cells before entering into contact with the phage virus, one would expect that some of these cells would form new resistant colonies on the respread dish and so to find a higher number of surviving bacteria there. When both plates were incubated for growth, there were actually as much as 50 times greater number of bacterial colonies on the respread dish. This showed that bacterial mutations to virus resistance had randomly occurred during the first incubation. Once again, the mutations occurred before selection was applied.

More recently, the results of Luria and Delbrück were questioned by Cairns and others, who studied mutations in sugar metabolism as a form of environmental stress. However, eventually this result was found to have been caused by selection for gene amplification and/or a higher mutation rate in cells unable to divide. Nevertheless, there is no evidence yet for directed mutagenesis: only those mutations that allow the cells to respond to the environmental stress accumulate in a growing population.

References

External links

• On Mutation lab