, viz., the cerebrum,
cerebellum, and the medulla oblongata, respectfully; and (2) the several
great centres of nerve substance in the human system, called the plexi,
such as the solar plexus, etc.

The vibrations arising from emotional excitement are sent out principally
from the plexi, or great centres of the sympathetic nervous system. Those
arising from the more strictly mental states emanate from certain centres
and points of the brain, or brains, of the person manifesting them.
Certain forms of these vibrations constitute the real essence of what is
generally called "human magnetism," which will be treated upon in the
proper place in these lessons.

I do not think it advisable to go into the technical details of the
generation and mechanism of transmission of these thought and emotional
vibrations, in these lessons. To understand the same would require a
technical knowledge of physiology and organic chemistry, which is not
possessed by the average person. Moreover, such details are neither
interesting nor instructive to the general student of occultism. But, I
think it proper to give at least a brief description of the receiving of
such vibratory-waves by other individuals.

In the first place, every great plexus, or groups of nerve ganglia, in the
human system is a receiving station, as well as a sending station. A
person manifesting strong emotional excitement tends to awaken similar
states in the nervous centres of other persons in whom the conditions are
favorable. This explains why the vibrations of anger, fear, panic, are so
contagious. It also explains the strong effect of the vibrations emanating
from the nerve centres controlling the reproductive system, in certain
cases of strong sexual excitation. Each human sympathetic nervous system
contains many receiving stations where emotional vibrations are received,
and where they tend to be transformed into similar feeling in the
receiving system, unless neutralized by other mental and emotional states
in the person.

When we come to consider the apparatus by which is received the vibrations
arising from what may be called "purely mental" operations of the brain,
such as intellectual thought, constructive imagination, etc., we find a
more specialized arrangement, as might be expected. There are several
minor receiving points of mental vibrations, regarding which I do not
consider it worth while to go into detail, because of the technical
features involved.