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