of the heart has the capacity of
containing about six ounces of blood, and every heart beat drives this
amount through the aorta. With seventy beats to the minute, twenty-five
pounds of blood is pumped from the heart every minute. What is the
result? That the four grams of iron keep up such an incessant movement
that they pass from the heart into the aorta sixty times an hour or 1440
times in 24 hours. It may be asserted, therefore, that in 24 hours 13
pounds of iron (that is 1440x4 grams) pass from the heart into the
aorta. Can it be doubted, in view of this, that the iron serves to
produce an electro-dynamic force?

In respect to the generation of electricity, it matters not whether
there be an entirely new supply of iron passing a given point, or
whether the same iron pass that point anew each minute. Two factors work
together in the circulation of the blood, namely, the active attraction
of nerve tissue and the passive susceptibility of the blood contents to
that attraction. Faraday has conclusively shown that blood is magnetic
in character because of the iron it contains. If four grams of iron is
the normal quantity in the blood, it is clear that the reduction of this
amount, say by two grams, will lessen its susceptibility and slacken its
circulation. The electrical nerve ends will then strain in vain for the
electricity which the blood current should yield, and the result will be
neuralgia.

It is the magnetic iron in haemoglobin which makes every sort of
nervous function possible, in the cerebral (brain) and in the
sympathetic (intestinal) tracts, and since it is thus made clear that
intellectual activity on the one hand and breathing and digestion and
excretion on the other are dependent on the iron content of the blood,
we must also recognize that, as iron attends every nerve action, the
secretion of urine too takes place under the influence of haemoglobin.
Insofar as haemoglobin hastens the departure of the excrementitious
matter in urine out of the system, there is a daily loss of iron in the
urine. This loss in the form of urohaematin may total four centigrams,
or a hundredth part of our supply.

This loss of iron if not replaced by eating suitable food will soon make
itself felt. In the course of a day the reduction by four centigrams
will diminish the energy of nervous activity about 1440 times the
apparent loss, so that even a four weeks-tropical fever, during which no
meat is eaten, may completely ex