patients by their answers and the facial changes caused by emotion, but
medico-legal experts naturally prefer a scientific test by means of
accurate instruments, by which the exact degree of emotion is
registered. These instruments are the plethysmograph and the
hydrosphygmograph.

=FIG. 28
Criminal's Ear=

It is well known that any emotion which causes the heart-beats to
quicken or become slower makes us blush or turn pale, and these
vaso-motor phenomena are entirely beyond our control. If we plunge one
of our hands into the volumetric tank invented by Francis Frank, the
level of the liquid registered on the tube above will rise and fall at
every pulsation, and besides these regular fluctuations, variations may
be observed which correspond to every stimulation of the senses, every
thought and above all, every emotion. The volumetric glove invented by
Patrizi (see Fig. 25), an improvement on the above-mentioned instrument,
is a still more practical and convenient apparatus. It consists of a
large gutta-percha glove, which is put on the hand and hermetically
sealed at the wrist by a mixture of mastic and vaseline. The glove is
filled with air as the tank was with water. The greater or smaller
pressure exercised on the air by the pulsations of blood in the veins of
the hands reacts on the aerial column of an india-rubber tube, and this
in its turn on Marey's tympanum (a small chamber half metal and half
gutta-percha). This chamber supports a lever carrying an indicator,
which rises and falls with the greater or slighter flow of blood in the
hand. This lever registers the oscillations on a moving cylinder covered
with smoked paper. If after talking to the patient on indifferent
subjects, the examiner suddenly mentions persons, friends, or relatives,
who interest him and cause him a certain amount of emotion, the curve
registered on the revolving cylinder suddenly drops and rises rapidly,
thus proving that he possesses natural affections. If, on the other
hand, when alluding to relatives and their illnesses, or vice-versa, no
corresponding movement is registered on the cylinder, it may be assumed
that the patient does not possess much affection.

=FIG. 25
A VOLUMETRIC GLOVE
(see page 224)=

=FIG. 26
HEAD OF A CRIMINAL
Epileptic=

Thus when Bianchi and Patrizi spoke to the notorious brigand Musolino
about life in his native woods, his mother, and his sweetheart, there
was an immediate alte