The name is absent

Vitamin Bi             175

mal for several days. The method is a good one except that
it requires an expensive electrocardiograph.

In the last few years other methods of testing for thiamin
in blood, urine, and foods have been developed. One meth-
od is to find how much of the tested substance is needed to
supply enough thiamin to allow a certain mold to grow in a
thiamin-free sugar solution. Another is to test its effect on
production of alcohol by yeasts. As little as one-millionth of
a gram can be detected in this way. There are chemical color
tests which are useful in studying body saturation, excretion,
etc., but they have not yet been very extensively used for the
testing of foods. It is difficult to extract all the thiamin pres-
ent in foods, and it is doubtful whether even the body accom-
plishes this during digestion, so the actual vitamin B₁ activity
of a food still has to be tested by biological assays on rats,
pigeons, or other animals.

The international unit of vitamin B₁ is based on the bio-
logical activity of a certain amount of a standard extract of
rice polishings adsorbed on Fuller’s earth. The unit is
equivalent to about 3⅛ micrograms (.0033 mg.) of thiamin.
Sometimes “Sherman” units are found on labels; roughly a
Sherman unit equals 2 to 3 international units.

Unlike vitamin A, thiamin is stored in the body in rather
limited amounts, the largest reserves being in the liver, kid-
neys, pancreas, and heart. For this reason it is even more
important than with most vitamins that the required amount
of thiamin be included in each day’s food.

Although vitamin B₁ is very widely distributed in Nature,
it cannot be said to be abundant in any common foods. There
is no single food that can be relied upon to supply the major
part of a day’s requirement. Even the richest sources con-
tain only 20 to 30 parts per million by weight, and most
common foods not more than from 0.1 to 4 parts per mil-

<<   4   5   6   7   8   9   10   >>

More intriguing information