BEST 619
rial is subsequently minced into acid alcohol. Robertson and
Anderson (8) use alcohol as the extractive. They advocate the
addition of sodium sulphate as a dehydrating agent, to the alco-
holic filtrate from the glands. Moloney and Findlay (9) have
recently published a second method based on the sorption of
insulin. Charcoal is used as the sorper in this method.
Several groups of observers believe that water is a satis-
factory extractive for insulin. Murlin (10) and his collabora-
tors have used both alcohol and water as extractives. Using the
latter, they have compared the yields of insulin obtained from
the pancreas by perfusion, percolation and simple extraction.
The fact that perfusion yielded the greatest amounts of insulin
is of physiological interest. Dodds and Dickens (11) have re-
Iported the successful use of aqueous formic acid (1 per cent)
as an extractive for insulin. These workers applied Dudley's
method for the purification of the product. Very recently Dodds
and Dickens (12) have reported favorable results with certain
procedures which differ very considerably from their original
method. The aqueous extraction is abandoned and extraction
with acetone of glands which have been thoroughly minced and
mnixed with powdered picric acid, is substituted. We have been
unable thus far to secure any better results with any of the
above-mentioned methods than with the acid alcohol extraction
method which we have used for the past half year for the prep-
aration of material for clinical use. This method is essentially
similar to that described by Scott and the writer (13). Detailed
reference to the methods used in Toronto is given in this article.
We find alcohol very strongly acidified with sulphuric acid, the
most satisfactory extractive. The use of strong acid at this stage
is advised by Somogyi, Doisy and Shaffer (14). In the search
for better methods for the preparation of insulin many new
properties of the substance have been discovered. This will
undoubtedly result in the eventual development of very eco-
nomical methods of production.
THE PROBLEM OF TESTING
Several methods of testing insulin are in use. The rabbit
method is used by the Insulin Committee of the University of
Toronto. A fornimula which facilitates the calculation of the
potency in units per cubic centimeter is used. This method was