om the body.

He had observed that the skin played an important part in cooling the
body, but he seems to have believed that the heart was equally active
in overheating it. The skin, therefore, absorbed air for the purpose of
"cooling the heart," and this cooling process was aided by the brain,
whose secretions aided also in the cooling process. The heart itself was
the seat of courage; the brain the seat of the rational soul; and the
liver the seat of love.

The greatness of Galen's teachings lay in his knowledge of anatomy of
the organs; his weakness was in his interpretations of their functions.
Unfortunately, succeeding generations of physicians for something like a
thousand years rejected the former but clung to the latter, so that the
advances he had made were completely overshadowed by the mistakes of his
teachings.

XI. A RETROSPECTIVE GLANCE AT CLASSICAL SCIENCE

It is a favorite tenet of the modern historian that history is a
continuous stream. The contention has fullest warrant. Sharp lines of
demarcation are an evidence of man's analytical propensity rather than
the work of nature. Nevertheless it would be absurd to deny that the
stream of history presents an ever-varying current. There are times
when it seems to rush rapidly on; times when it spreads out into a
broad--seemingly static--current; times when its catastrophic changes
remind us of nothing but a gigantic cataract. Rapids and whirlpools,
broad estuaries and tumultuous cataracts are indeed part of the same
stream, but they are parts that vary one from another in their salient
features in such a way as to force the mind to classify them as things
apart and give them individual names.

So it is with the stream of history; however strongly we insist on its
continuity we are none the less forced to recognize its periodicity. It
may not be desirable to fix on specific dates as turning-points to the
extent that our predecessors were wont to do. We may not, for example,
be disposed to admit that the Roman Empire came to any such cataclysmic
finish as the year 476 A.D., when cited in connection with the overthrow
of the last Roman Empire of the West, might seem to indicate. But, on
the other hand, no student of the period can fail to realize that a
great change came over the aspect of the historical stream towards the
close of the Roman epoch.

The span from Thales to Galen has compassed about eight hundred
years--let us say thirty generations