methods have be devised to attain the maximum purity. The authors
recommend the following procedure:

_a_. To purify the casein or other protein used. Boil the protein
three successive times (it is assumed that the original is already as pure
as it is possible to obtain it by the usual methods of preparation) for an
hour each time, with absolute alcohol, using a reflux condenser to prevent
loss of alcohol. Filter off the alcohol each time by suction. This process
will take off all the adherent fat and hence all the "A" vitamine that
might be present. The casein is then dried and ready for use. In certain
experiments the authors use meat residues instead of a single protein.
This they prepare as follows: Fresh lean round of beef is run through a
meat chopper and then ground to a paste in a Nixtamal mill, stirred into
twice its weight of water and boiled a few minutes. The solid residue is
then strained, using cheese cloth, pressed in the hydraulic press and the
cake stirred into a large quantity of boiling water. After repeating this
process of washing with hot water the extracted residue is rapidly dried
in a current of air at about 60 C. This dried residue may then be further
purified with the absolute alcohol treatment as described for casein.

_b_. To purify the carbohydrate they treat starch in exactly the same
way as the casein.

_c_. To purify the lard. This is melted and poured into absolute
alcohol previously heated to 60 C., cooled over night and filtered by
suction. This process is repeated three times and the resulting solids
dried in a casserole over a steam bath.

_d_. When butter fat is used to provide a source of "A" vitamine it
is prepared as follows: Butter is melted in a flask on a water bath at