British explanation but at the same time reiterate their belief that even
commercial lard contains no "A" vitamine. Whatever the explanation of this
particular phenomenon it is important that the basal diet be of purified
materials and the methods just described supply the procedure necessary to
attain that end.

Before discussing the application of these diets to vitamine testing,
attention is called to other basal diets developed by McCollum. This
worker has paid especial attention to the deficiencies of the cereal
grains and in particular to their salt deficiencies. In his basal diets,
we find, as would be expected, special combinations particularly suited to
the detection of vitamines in such cereals. McCollum has also devised a
method of extracting substances to obtain their "B" vitamine and of
depositing it on dextrin. For that reason he uses dextrin instead of
starch for his carbohydrate and when he wishes to introduce the "B"
vitamine it can be done by his method without having to recalculate the
carbohydrate component. His method consists of first extracting the source
with ether and discarding this extract. Pure ether will not remove the "B"
vitamine. The residue is then reextracted several times with alcohol and
the alcohol extracts combined. If now these alcohol extracts are
evaporated down on a weighed quantity of dextrin the activated dextrin can
be used not only to supply the carbohydrate of the ration but also to
carry the "B" vitamine of a given source that is under investigation.
McCollum's basal diets and salt mixtures are tabulated in the following
chart:

_McCollum's basal diets and salt mixtures_

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