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47° MODERN TIMES.
Other investigators threw light upon the mechanism of
respiration, the functions of the muscles which take partin
it, the interchange of gases in the lungs and the relation
this bears to the colour of the blood; they attempted alsoto
measure the force exerted by the lungs in inspiration
and expiration, as well as the volume of air employed in
these acts. The foundation of spirometric and manometric
measurements of lung capacity, by which some help,
is given in diagnosing pulmonary diseases, was the work
of JOHN HUTCHINSON and WALDENBURG.
The phenomena of motion also aroused earnest attention.
Ciliary movement, which had before been thought to be
limited to the lower animals, was observed by PURKINJE in
the human body also ; molecular movement only came,
under observation in quite recent times. The mechanism.
of human locomotion was well-nigh exhaustively treated by
the brothers EDUARD and WILHELM WEBER.
The discovery of electric currents in muscles directed;
attention to the chemical and physical processes which
take place in the interior of muscles. In the same way,
the electricity of the nerves suggested a multitude of
problems, the solution of which still occupies the minds of
philosophers and investigators* I have already pointed
out how important for forming a judgment upon the acts
performed by the organism is the law of the conservation
and metamorphosis of energy discovered by J. R. MAYER.
In 1811, CHARLES BELL raised into the position of a
scientific fact the anatomical distinction, already suspected
by GALEN, between the motor and sensory nerves, by
bringing forward the proof that the former arise from the
anterior, the latter from the posterior roots on the spinal
cord. He hit upon a discovery of such extraordinary
importance for the physiology of the nerves by a comparative
study of the anatomical and physiological relations
of the cranial nerves and especially of the two roots of the
* E. DU BOIS-REYMONO : Untersuchungen iiber thierische Elektricitat, Berlin
1848, Bd. i, S. 29 et seq.