when Haller's theory was found to be entirely
correct.

It was in pursuit of experiments to establish his theory of irritability
that Haller made his chief discoveries in embryology and development. He
proved that in the process of incubation of the egg the first trace of
the heart of the chick shows itself in the thirty-eighth hour, and that
the first trace of red blood showed in the forty-first hour. By his
investigations upon the lower animals he attempted to confirm the theory
that since the creation of genus every individual is derived from a
preceding individual--the existing theory of preformation, in which
he believed, and which taught that "every individual is fully and
completely preformed in the germ, simply growing from microscopic to
visible proportions, without developing any new parts."

In physiology, besides his studies of the nervous system, Haller studied
the mechanism of respiration, refuting the teachings of Hamberger
(1697-1755), who maintained that the lungs contract independently.
Haller, however, in common with his contemporaries, failed utterly to
understand the true function of the lungs. The great physiologist's
influence upon practical medicine, while most profound, was largely
indirect. He was a theoretical rather than a practical physician, yet he
is credited with being the first physician to use the watch in counting
the pulse.

BATTISTA MORGAGNI AND MORBID ANATOMY

A great contemporary of Haller was Giovanni Battista Morgagni
(1682-1771), who pursued what Sydenham had neglected, the investigation
in anatomy, thus supplying a necessary counterpart to the great
Englishman's work. Morgagni's investigations were directed chiefly to
the study of morbid anatomy--the study of the structure of diseased
tissue, both during life and post mortem, in contrast to the normal
anatomical structures. This work cannot be said to have originated
with him; for as early as 1679 Bonnet had made similar, although less
extensive, studies; and later many investigators, such as Lancisi and
Haller, had made post-mortem studies. But Morgagni's De sedibus et
causis morborum per anatomen indagatis was the largest, most accurate,
and best-illustrated collection of cases that had ever been brought
together, and marks an epoch in medical science. From the time of the
publication of Morgagni's researches, morbid anatomy became a recognized
branch of the medical science, and the effect of the impetus thus given
it