CHEMISTRY OF THE BRAIN: MOLECULES, MOOD, AND MENTAL ILLNESS - Chemistry: Notable Research and Discoveries - page 72

InTroduCTIon
The figure on page 71 shows a diagram of an adult human brain, which
weighs about three pounds (1.4 kg) on average. Early chemists who
studied the brain did not have instruments or techniques to separate
the components. All the chemists could do was crudely separate some
of the material by repeatedly using a solvent —a substance that dissolves
certain compounds—and other agents that bind to compounds, mak-
ing them insoluble.
Beginning in the 18th century and continuing through the 19th
century, the German scientist Johann Hensing (1683-1726), the French
scientists Michel-Augustin Thouret (1748-1810) and Louis-Nicolas
Vauquelin (1763-1829), and others discovered that the brain contains a
lot of fatty components. Fats are large molecules made of mostly carbon
and hydrogen, and they generally feel oily or buttery to the touch. About
half of the dry weight of the brain is composed of fats and lipids (fatty
compounds). (Dry weight means that the water has evaporated or been
removed.) Much of this fatty material was found in the brain's “white”
matter, which was named because it is generally pale, particularly when
the brain is removed and hardened with chemicals for study. (Brains are
so soft they cannot even support their own weight—one of the reasons
why brains must be encased in skulls for protection and surrounded by
fluid contained within cavities called ventricles and a porous structure
known as the meninges.) Researchers later showed that white matter
consists of the projections by which brain cells communicate with one
another. The fatty molecules wrap around these projections, acting as a
kind of insulation and aiding the communication process.
The brain's “gray” matter contains mostly cells. A cell is the funda-
mental unit of life in all organisms and contains enzymes, nutrients, and
genetic material within a thin membrane made of lipids and protein. The
human body contains cells that have different properties to perform dif-
ferent functions, such as skin cells, brain cells, muscle cells, and so on.
Brain cells are not actually gray but are mostly transparent, as are most
cells; however, collections of cells may appear gray or grayish brown un-
der certain circumstances, especially after the brain is chemically treated.
Two main types of cell exist in the brain—a glial cell serves important
maintenance and support functions, and a neuron processes information,
possibly aided by glial cells. The human brain contains about a trillion
neurons and several times that number of glial cells.