own and for a time exerted considerable
influence. But in the end his system was destined to pass out of
existence, not very long after the death of its author. Van Helmont
was not only a physician, but was master of all the other branches of
learning of the time, taking up the study of medicine and chemistry
as an after-thought, but devoting himself to them with the greatest
enthusiasm once he had begun his investigations. His attitude towards
existing doctrines was as revolutionary as that of Paracelsus, and he
rejected the teachings of Galen and all the ancient writers, although
retaining some of the views of Paracelsus. He modified the archaeus of
Paracelsus, and added many complications to it. He believed the whole
body to be controlled by an archaeus influus, the soul by the archaei
insiti, and these in turn controlled by the central archeus. His system
is too elaborate and complicated for full explanation, but its chief
service to medicine was in introducing new chemical methods in the
preparation of drugs. In this way he was indirectly connected with the
establishment of the Iatrochemical school. It was he who first used the
word "gas"--a word coined by him, along with many others that soon fell
into disuse.

The principles of the Iatrochemical school were the use of chemical
medicines, and a theory of pathology different from the prevailing
"humoral" pathology. The founder of this school was Sylvius (Franz de
le Boe, 1614-1672), professor of medicine at Leyden. He attempted to
establish a permanent system of medicine based on the newly discovered
theory of the circulation and the new chemistry, but his name is
remembered by medical men because of the fissure in the brain (fissure
of Sylvius) that bears it. He laid great stress on the cause of fevers
and other diseases as originating in the disturbances of the process of
fermentation in the stomach. The doctrines of Sylvius spread widely over
the continent, but were not generally accepted in England until modified
by Thomas Willis (1622-1675), whose name, like that of Sylvius, is
perpetuated by a structure in the brain named after him, the circle
of Willis. Willis's descriptions of certain nervous diseases, and an
account of diabetes, are the first recorded, and added materially to
scientific medicine. These schools of medicine lasted until the end of
the seventeenth century, when they were finally overthrown by Sydenham.

The Iatrophysical school (also called