childlike mind, but, little by little, such experiences crystallized
into useful knowledge. The experiments of nature made clear to him the
relation of cause and effect, but it is not likely, as Pliny suggests,
that he picked up his earliest knowledge from the observation of
certain practices in animals, as the natural phlebotomy of the plethoric
hippopotamus, or the use of emetics from the dog, or the use of enemata
from the ibis. On the other hand, Celsus is probably right in his
account of the origin of rational medicine. "Some of the sick on account
of their eagerness took food on the first day, some on account of
loathing abstained; and the disease in those who refrained was more
relieved. Some ate during a fever, some a little before it, others after
it had subsided, and those who had waited to the end did best. For the
same reason some at the beginning of an illness used a full diet, others
a spare, and the former were made worse. Occurring daily, such things
impressed careful men, who noted what had best helped the sick, then
began to prescribe them. In this way medicine had its rise from
the experience of the recovery of some, of the death of others,
distinguishing the hurtful from the salutary things" (Book I). The
association of ideas was suggestive--the plant eyebright was used for
centuries in diseases of the eye because a black speck in the flower
suggested the pupil of the eye. The old herbals are full of similar
illustrations upon which, indeed, the so-called doctrine of signatures
depends. Observation came, and with it an ever widening experience. No
society so primitive without some evidence of the existence of a healing
art, which grew with its growth, and became part of the fabric of its
organization.

With primitive medicine, as such, I cannot deal, but I must refer to
the oldest existing evidence of a very extraordinary practice, that of
trephining. Neolithic skulls with disks of bone removed have been found