g of pyramidal,
_earth_ of cubical, _air_ of octagonal, and _water_ of twenty-sided
atoms. The marrow consists of triangles, and the brain is the perfection
of marrow. The soul dominates the marrow and the separation of the two
causes death. The purpose of the bones and muscles is to protect the
marrow against changes of temperature. Plato divided the "soul" into
three parts: Reason, enthroned in the brain; courage in the heart; and
desire in the liver. The uterus, he believed, excites inordinate
desires. Inflammations are due to disorders of the bile, and fevers to
the influence of the elements. His theories in regard to the special
senses are very fantastic, for instance, smell is evanescent because it
is not founded on any external image; taste results from small vessels
carrying taste atoms to the heart and soul.

_Aristotle_, born B.C. 334, was the son of Nichomachus, physician to the
King of Macedonia, and of the race of the Asclepiads. His inherited
taste was for the study of Nature; he attained the great honour of being
the founder of the sciences of Comparative Anatomy and Natural History,
and contributed largely to the medical knowledge of his time. Aristotle
went to Athens and became a follower of Plato, and the close
companionship of these two great men lasted for twenty years. At the age
of 42, Aristotle was appointed by Philip of Macedon tutor to Alexander
the Great, who was then aged 15, and the interest of that mighty prince
was soon aroused in the study of Natural History. Aristotle and
Alexander the Great, teacher and pupil, founded the first great Natural
History Museum, to which specimens were sent from places scattered over
the then known world. Aristotle, besides his philosophical books, wrote:
"Researches about Animals," "On Sleep and Waking," "On Longevity and
Shortlivedness," "On Parts of Animals," "On Respiration," "On Locomotion
of Animals," and "On Generation of Animals." He was greatly helped in
the supply of material for dissection in his study of comparative
anatomy by his pupil, Alexander the Great. Aristotle pointed out the
differences in the anatomy of men and monkeys; he described the anatomy
of the elephant and of birds, and also the changes in development seen
during the incubation of eggs. He investigated, also, the anatomy of
fishes and reptiles. The stomachs of ruminant animals excited his
interest, and he described their structure. The heart, according to
Aristotle, was the seat