Physiology and Perception 95Imagine that the Sensorium is a prisoner in the skull and wants
to know about the Eiffel Tower. The only ways that it could
learn about it would involve having pictures of the tower, or
small copies of it (eidola) brought in, or failing that, at least a
verbal description of it. Notice that the representation of the
object to the mind is a real copy in kind. If there are no copies
of the object, or if the nerves cannot carry them, then we could
still have a symbolic representation of them, such as wordlike
symbols, as long as these have a fixed functional relationship
to the object so that the mind can recreate its properties by
inference. However, there was already some data that sug-
gested that images, or symbols representing images, were not
being passed down the nerves. For instance, Charles Bell
(1774–1842) pointed out that we perceive sensory qualities
based on the specific nerve that is stimulated, not on the basis
of the object providing the stimulation. If, for example, you
put pressure on the eyeball, you will stimulate the retina; how-
ever, what you perceive will be light, not pressure.
Müller introduced the concept that the Sensorium is only
directly aware of the states of the sensory nerves, not of the
external object. Each nerve can only transmit information
about one specific energy source, and there are five such
nerve energies, one for each of the senses. Thus, a stimulus
acting on a nerve that is tuned for visual energies will be per-
ceived as visual, regardless of whether the actual stimulus
was light, mechanical, or electrical stimulation. Finally, he
suggested that the actual specificity is recognized only at the
termination of the nerve in the brain. In doing this, he was in-
corporating the work of Pierre Flourens (1794–1867), who
had demonstrated that specific locations in the brain con-
trolled specific functions. Flourens based this upon data from
animals that had had parts of the brain systematically de-
stroyed and thus lost particular motor functions, as well as
various visual and auditory reflexes. Later on this would be
confirmed using human subjects who had head injuries due to
war or accident and who also suffered from sensory impair-
ments dependent on the location of the injury.
Müller’s break with the eidola theory was not complete,
however. He felt that each “adequate stimulus” impressed a
wealth of information on the appropriate neural channel by
exciting a vis viva(life force) or vis nervosa(neural power),
which took an impression of all the information that would
have been present had there been an actual eidola or image
present. In this he was expressing the old physiological doc-
trine of vitalism, which maintained that living organisms
were imbued with some special force that was responsible for
life and consciousness but not subject to scientific analysis.
This is very similar in tone to the concept of animal spirits
postulated by Descartes.
It was Müller’s students who would take the next steps. In
addition to his writing and research, Müller was a splendid
teacher who attracted many brilliant students. Among these
was Hermann Helmholtz (1821–1895), who played a pivotal
role in this history, and his classmates Émile du Bois-Reymond
(1818–1896), who later collaborated with Helmholtz and
gained fame by establishing the electrochemical nature of the
nervous impulse; Rudolf Virchow (1821–1902), who later pi-
oneered the cellular theory of pathology; and Ernst Brücke
(1819–1893), who would later do work on the interactions be-
tween color and brightness but who would be best known as
the most influential teacher of Sigmund Freud. Together these
students rejected the idea that there was any life force that was
so mysterious that it could not be analyzed, and so different
that it did not follow the know rules of physics and physiology.
As a rebellion against vitalism, they drew up a solemn article of
faith in the mechanistic viewpoint, which stated thatNo other forces than the common physical-chemical ones are
active within the organism. In those cases which cannot at the
time be explained by these forces one has either to find the spe-
cific way or form of their action by means of the physical math-
ematical method, or to assume new forces equal in dignity to
the physical-chemical forces inherent in mater, reducible to the
force of attraction and repulsion. (Bernfeld, 1949, p. 171)Then, with the passion generated by youthful fervor for a
cause, they each signed the declaration with a drop of their
own blood. It is ironic, in some ways, that a blood oath, so
common in mysticism and magical rites, would be the begin-
ning of a movement to purge spirits, demons, spirits, and the
soul from psychology.
The full implications of specific nerve energies were not
immediately apparent, but this idea would come to change the
nature of perceptual research. In 1844, Natanson made the ob-
vious mechanistic extension when he argued that every neural
organ must have a function and conversely every function
must have an organ. In sensory terms, he thought that there
might be three different energies for touch, three for taste,
three for vision, and an indeterminate number for smell. In
that same year, A. W. Volmann attempted to criticize Müller
on the ground that his theory would require not merely five
specific energies but one for every sense-quality. This might
require different channels for pressure, temperature, pain,
every one of the 2,000 recognizable colors, every discrim-
inable taste, and so forth. At the time, this seemed like almost
a reductio ad absurdum, since it seemed to require an infinity
of specific channels for the infinity of specific perceived sen-
sory qualities. However, a solution would show itself.