254 Aqueous Extracts of Pancreas. I
dure (3) there was with two dogs in four trials a rise of the res.
piratory quotient of 10 to 18 points above the predetermined
diabetic level, indicating a restoration in part of the power to
oxidize glucose.
The work was unavoidably interrupted at this point, but
was resumedbythe senior author in October, 1921, with the convic.
tion that assiduous searchwould discloseamethodof extraction and
purification of the antidiabetic substance (insuline, Schafer (5))
produced by the pancreas in a form capable of administration to
diabetic human subjects. The starting point was the method of
extraction employed by Murlin and Kramer in 1913; namely,
maceration of the freshly removed pancreas in 0.2 N HCl and
neutralization of the extract before administration. It was known
from previous experience that such extracts not purified further
are somewhat toxic. But it was believed that the toxic substance
could be removed once the presence of the antidiabetic substance
was extracted in sufficient amount to have significant therapeutic
value. The method of purification in mind and subsequently
employed was that used by Zuelzer (6) and his colleagues in 1908
and adopted by Collip (7) in purifying Banting's extract for
administration to human beings; namely, precipitation of extrane-
ous proteins by means of alcohol. Zuelzer unquestionably had
a potent extract, but he did not succeed in removing all the toxic
substances, and in the letters patent (8) granted by the U. S.
Patent Office in 1912 admission is made that the extract was "too
septlc to be used for persons." Nevertheless, both Zuelzer (6)
and Forschbach (9) had demonstrated the presence of an anti-
diabetic substance both experimentally on dogs and clinically.
The efforts of Blumenthal (10) and of Croftan (11), who as far
as we are aware was the first to act specifically upon the hypothesis
that the hormone was destroyed by trypsin,' were also distinctly
encouraging as was, of course, the more recent success of Kleiner
(13) in reducing the blood sugar of depancreatized dogs by means
of suspensions in sterile water of macerated fresh pancreas of the
dog.
x The use of hest for the purpose of destroying the external en,zymes
had been used earlier by Leschke (12), but he was acting on just the opposite
theory from Croftan; namely, that such effects as one gets from extract of
pancreas on carbohydrate metabolism are due to the external enzymes
themselves.