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Physiology
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Introduction; History of Physiological Investigation; Recent Advances
III
RECENT ADVANCES
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Among the most important advances of the 20th century are the
discovery of new hormones; recognition of the role of vitamins;
discovery of blood types; development of the electrocardiograph
and electroencephalograph, to record the activity of the heart
and brain; discovery of the cause and cure of pernicious anemia
by George Richards Minot, William Parry Murphy, and George
Hoyt Whipple, all American physicians; and greater
understanding of metabolism, the role of enzymes, and the
immune system.
The first part of the 20th century also witnessed great advances
in the understanding of reflexes, first elaborated by the French
philosopher René Descartes as a philosophic concept to
distinguish involuntary reflexes of animals from the more
rational reactions of humans. The concept was refined by the
work of German zoologists, who described it in physical terms
and divided behavior into its component reflexes. Further
understanding was facilitated by the British neurophysiologist
Sir Charles Sherrington, who showed that reflexes enable the
nervous system to function as a unit. The concept of a

2. conditioned response, first described in the 18th century by the
Scottish physiologist Robert Whytt, a pioneer in the study of
reflex action, culminated in the later work of the Russian
physiologist Ivan Pavlov and that of the Russian
neuropathologist Vladimir Bekhterev. Although there was no
validity to Pavlov's attempt to extend the principles of
conditioning—the method by which responses may be elicited
more frequently or more predictably by reinforcement—to
complex mental processes, his work had great impact on
psychology and learning. It was one of the primary influences in
the founding of behaviorism by the American psychologist John
B. Watson; the work of the American psychologist B. F. Skinner
in programmed instruction, the basis of so-called teaching
machines, was also based on the theory of conditioning and
reinforcement.
The 20th century has also witnessed other fundamental
advances