temperament are perhaps caused more by the different distribution and
quantities of the inorganic salts than by everything else. Bilious
people have too little sodium sulfate, the melancholics are lacking in
potassium sulfate and phosphate; too little calcium phosphate in the
phlegmatics. Courageous natures have an excess of iron phosphate." (See
volume 12 of _Nietzsche's Works_, edit. Naumann-Kroener, Leipzig, 1886.)
In this strange association of inorganic salts with human temperaments,
the role of iron phosphate as a producer of courage is particularly
interesting. What would a modern philosopher conclude if he followed the
development of insight into the composition and function of complex
phosphate compounds in organisms?

From Inorganic to Organic Phosphates

By the middle of the 19th century, the source of phosphorus in natural
phosphates and the chemistry of its oxidation products had been
established. The main difficulty that had to be overcome was that these
oxidation products existed in so many forms, not only several stages of
oxidation, but, in addition, aggregations and condensations of the
phosphoric acids. Once the fundamental chemistry of these acids was
elucidated, the attention of chemists and physiologists turned to the
task of finding the actual state in which phosphorus compounds were
present in the organisms. It had been a great advance when it had been
shown that plants need phosphates in their soil. This led to the next
question concerning the materials in the body of the plant for which
phosphates were being used and into which they were incorporated.
Similarly, the knowledge that animals attain their phosphates from the
digested plant food called, in the next step of scientific inquiry, for
information on the nature of phosphates produced from this source.

The method used in this inquiry was to subject anatomically separated
parts of the organisms to chemical separations. The means for such
separations had to be more gentle than the strong heat and destructive
chemicals that had been considered adequate up to then. The
interpretation of the new results naturally relied on the general
advance of chemistry, the development of new methods for isolating
substances of little stability, of new concepts concerning the
arrangements of atoms in the molecules, and of new apparatus to measure
their rates of change.

In the system of chemistry, as it developed in the first half of the
19th c