ter, _Pleurotus ulmarius_
gives 12.6 per cent., and _Clitopilus prunulus_ gives 15 per cent. The
average of twelve edible species gave 7 per cent. ash in the stem and
8.96 per cent. in the cap.

In regard to the constituents of the ash, potassium is by far the most
abundant--the oxide averaging about 50 per cent. of the total ash.
Phosphoric acid stands next to potassium in abundance and importance,
constituting, on an average, about one-third of the entire ash. Oxides
of manganese and iron are always present; the former averaging about 3
per cent. and the latter 5 per cent. to 2 per cent. of the ash. Sodium,
calcium, and chlorine are usually present in small and varying
quantities. Sulphuric acid occurs in the ash of all fungi, and is
remarkable for the great variation in quantity present in different
species; e. g., ash of _Helvella esculenta_ contains 1.58 per cent.
H_2SO_4 while that of _Agaricus campestris_ contains the relatively
enormous amount of 24.29 per cent.

Any discussion of the bare composition of a food is necessarily
incomplete without a consideration of the nutritive value of the various
constituents. This is especially desirable in the case of the mushrooms,
for while they are frequently overestimated and occasionally
ridiculously overpraised by their friends, they are quite generally
distrusted and sometimes held in veritable abhorrence by those who are
ignorant of their many excellent qualities. On the one hand, we are told
that "gastronomically and chemically considered the flesh of the
mushroom has been proven to be almost identical with meat, and possesses
the same nourishing properties." We frequently hear them referred to as
"vegetable beefsteak," "manna of the poor," and other equally
extravagant and misleading terms. On the other hand, we see vast
quantities of the most delicious food rotting in the fields and woods
because they are regarded by the vast majority of the people as
"toadstools" and as such particularly repulsive and poisonous.

Foods may be divided into three classes according to the functions they
perform:

(_a_) To form the material of the body and repair its wastes.

(_b_) To supply energy for muscular exertion and for the maintenance of
the body heat.

(_c_) Relishes.

The formation of the body material and the repair of its wastes is the
function of the proteids of foods. It has been found by careful
experiment that a man at moderately hard muscular exertion requir