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3. RESEARCHER IN HELSINKI, OXFORD AND PHILADELPHIA
 In 1928 Ragnar Granit travelled to Oxford University, just two years after Professor Edgar D. Adrian
had been the first to measure the electric impulse of a single nerve. The most notable nerve physiologist of the time,
Sir Charles Scott Sherrington, was then working at Oxford. Granit wanted to understand vision and
realized that the underlying fact was that the retina itself functions as a nerve centre which processes
visual information and transmits already processed information to the brain's visual centre.
Using the electric measuring technique developed by Edgar Adrian, Granit continued bioelectric research
at the University of Pennsylvania as researcher in medical physics from 1929 to 1932. After that he was back again
at Sherrington's laboratory during the years 1932-1933. He continued his electroretinogram (ERG) bioelectric research
on the visual nerve and the retina at the University of Helsinki from 1935 to 1940. Granit's book Sensory Mechanisms of the Retina
published in 1947 is one of the classics in the field of the electrophysiology of the eye.
One of Sherrington's central thoughts was that the effect of nerve signals on the next nerve cell, via a synapse,
can be either activating or inhibiting. Granit became interested in the idea of being able to demonstrate experimentally
that the retina also contained inhibiting synapses. After leaving Sherrington and returning home to Helsinki,
he succeeded in this experiment. In this work he used a self-made electron valve amplifier. He published his research results in 1935.
However, this work was not yet applied to a single nerve cell. In his further work, also carried out in Helsinki,
Granit performed an experiment on a single nerve cell. The preparation involved an insulated frog's eye
which had just been opened. For this he required an extremely small electrode. In his measurements he used
an especially sharp silver needle insulated with a glass capillary tube. The glas capillary had been melted round
the whole silver needle except for the head of the needle. This type of electrode was the first of its kind
and was to be used later as in instrument in countless other electro-physiological research experiments.
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Granit further pursued the physiological basis of colour perception. According to his research results,
some nerve fibres of the eye are not particularly selective in the case of colour. On the contrary,
they react in the same way over the whole spectrum. In contrast, other fibres clearly distinguish between colours.
In 1937 Granit published these research results, thus confirming the theory of colour perception
put forward in his own day by Hermann von Helmholtz (1821-1894).
Together with another physiologist from Helsinki, Gunnar Svaetichin, Granit observed that the electric impulses
generated in the retina, the so-called electroretinogram, showed that sensitivity to colour is concentrated mainly
in three different groups in the area of blue, green and red. This provided the first biological demonstration
in support of the Young-Hemholz three-colour theory.
In 1929 Ragnar Granit was appointed Docent in Physiology, and in 1937 Swedish-language Professor of Physiology
at the University of Helsinki. In 1940, when the Winter War between Finland and Russia had ended, he was appointed Research Professor at Harvard University in the United States. It is known that he had already bought the travel tickets to the United States when he received the offer to become Professor of Neurophysiology at Karolinska Institutet of Stockholm. He decided in favour of the latter. In 1945 the Neurophysiology Laboratory of the Nobel Institute of Medicine in Stockholm was founded. He was invited to become its director and worked in this position until his retirement in 1967.
Ragnar Granit was also Visiting Professor at the Rockefeller Institute in New York during the years 1956-1966,
at St. Catherine's College, Oxford in 1967, at the University of the Pacific, San Francisco in 1969,
at the University of Düsseldorf in 1975, at the Max-Planck Institute (Bad Nauheim) in 1976 and
at the National Institute of Health (Bethesda, Maryland, USA) in 1971-1972 and 1974.
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