Encyclopedia of Biology

their cleavage products), 1881; Die Gewebe des men-
schlichen Körpers und ihre mikroskopische Unter-
suchung (The tissues in the human body and their
microscopic investigation), 1889–91, in two volumes,
with Behrens and Schieerdecker; and Leitfaden für
medizinisch-chemische Kurse (Textbook for medical-
chemical courses), 1888. He was also the author of Die
Probleme der Biochemie(The problems of biochem-
istry), 1908; and Die Beziehungen der Chemie zur
Physiologie(The relationships between chemistry and
physiology), 1913.
Kossel had honorary doctorates from the Universi-
ties of Cambridge, Dublin, Ghent, Greifswald, St.
Andrews, and Edinburgh, and he was a member of var-
ious scientific societies, including the Royal Swedish
Academy of Sciences and the Royal Society of Sciences
of Uppsala. Albrecht Kossel died on July 5, 1927.

Krakatoa An island volcano along the Indonesian
arc, between the islands of Sumatra and Java. Krakatoa
erupted in 1883 in one of the largest eruptions in histo-
ry and was heard as far away as Madagascar (2,200
miles). The volcanic dust veil that created spectacular
atmospheric effects, like vivid red sunsets, acted as a
solar radiation filter, lowering global temperatures as
much as 1.2°Cin the year after the eruption. Tempera-
tures did not return to normal until 1888.

Krebs, Sir Hans Adolf(1900–1981) GermanBio-
chemist Sir Hans Adolf Krebs was born in
Hildesheim, Germany, on August 25, 1900, to Georg
Krebs, M.D., an ear, nose, and throat surgeon of that
city, and his wife Alma (née Davidson).
Krebs was educated at the Gymnasium Andreanum
at Hildesheim. Between 1918 and 1923 he studied
medicine at the Universities of Göttingen, Freiburg-im-
Breisgau, and Berlin. He received an M.D. degree at the
University of Hamburg in 1925. In 1926 he was
appointed assistant to Professor Otto Warburg at the
Kaiser Wilhelm Institute for Biology at Berlin-Dahlem,
wherehe remained until 1930. He was forced to leave
Germany in 1933 because of his Jewish background.
In 1934 he was appointed demonstrator of bio-
chemistry at the University of Cambridge, and the fol-
lowing year was appointed lecturer in pharmacology at
the University of Sheffield. In 1938 he became the

newly founded lecturer-in-charge of the Department of

Biochemistry. In 1939 he became an English citizen. By

1945 he was a professor and director of the Medical

Research Council’s research unit established in the

department. In 1954 he was appointed Whitley Profes-

sor of Biochemistry in the University of Oxford, and

the Medical Research Council’s Unit for Research in

Cell Metabolism was transferred to Oxford.

At the University of Freiburg in 1932, he discov-

ered a series of chemical reactions (now known as the

urea cycle) by which ammonia is converted to urea in

mammalian tissue. For his discoveries of chemical reac-

tions in living organisms now known as the citric acid

cycle or the Krebs cycle, he was awarded the 1953

Nobel Prize in physiology or medicine. These reactions

involve the conversion, in the presence of oxygen, of

substances that are formed by the breakdown of sug-

ars, fats, and protein components to carbon dioxide,

water, and energy-rich compounds.

Krebs was a member of many scientific societies,

winning many awards and citations for his work, and

published works including Energy Transformations in

Living Matter (1957) with British biochemist Hans

Kornberg. He was knighted in 1958. He died on

November 22, 1981, in Oxford, England.

Krebs cycle A biochemical cycle in the second stage

of cellular respiration involving eight steps that com-

pletes the metabolic breakdown of glucose molecules

to carbon dioxide. Acetyl coenzyme A (CoA) is com-

bined with oxaloacetate to formcitric acid. Citric acid

is then converted into a number of other chemicals,

and carbon dioxide is released. The process takes

place within the mitochondrion. Also called the citric

acid cycle or tricarboxylic acid (TCA) cycle, it was

conceived and published by scientist Hans Adolf

Krebs in 1957.

Krogh, Schack August Steenberg(1874–1949)

DanishPhysiologist Schack August Steenberg

Krogh was born in Grenaa, Jutland, Denmark, on

November 15, 1874, to Viggo Krogh, a shipbuilder,

later brewery master, and Marie Drechmann. He

earned his upper secondary school diploma at the

Cathedral School of Århus in 1893 and entered the

University of Copenhagen in 1893. He began his

Krogh, Schack August Steenberg 191