The first lessons came to primitive man by injuries, accidents, bites of beasts and serpents, perhaps for long ages not appreciated by his 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 in nearly all parts of the world. Many careful studies have been made of this procedure, particularly by the great anatomist and surgeon, Paul Broca, and M. Lucas-Championniere has covered the subject in a monograph.(2) Broca suggests that the trephining was done by scratching or scraping, but, as Lucas-Championniere holds, it was also done by a series of perforations made in a circle with flint instruments, and a round piece of skull in this way removed; traces of these drill-holes have been found. The operation was done for epilepsy, infantile convulsions, headache, and various cerebral diseases believed to be caused by confined demons, to whom the hole gave a ready method of escape. (2) Lucas-Championniere: Trepanation neolithique, Paris, 1912.