68 GENIUS AND MENTAL DISEASE. 
from the fact that the sense-centers are influenced by im- 
pressions received independent -of their source. Their 
function is to transform impressions into conscious sen- 
sation, and hence an idea or emotion, when directed in 
a special way with persistent, concentrated force, may 
so impress the sensorium as to cause it to project into 
consciousness sensations which seem to come from ob- 
jects in the external world. I cannot tell how this is 
done, neither can I tell how it is done when impressions 
come from without. The facts we know, but the secrets 
of transformation elude us. The brain constructs new 
forms, but conceals the methods of imagination by the 
shadow of unconsciousness. 
Ajax becomes enraged because the arms of Achilles 
are given to Ulysses, and in his wrath he sees animals 
as Greeks and assails them as if Ulysses and Agamem- 
non themselves were before him. ‘Talma intensified his 
emotions and his dramatic effect by the illusive specters 
of his mind. Spinoza beheld with great distinctness the 
disagreeable image of his dream a long time after sleep 
was gone; and Niebuhr, when describing the scenes of 
his travels, would see all rise before him in ‘‘all the 
coloring, animation; and splendor of nature.” 
Multitudes have been at times subject to the same 
false perceptions ; as when the soldiers under Constan- 
tine saw the cross in the sky bearing the inscribed 
words, ‘‘/n hoc signo vinces”’; or when the army at 
the battle of Antioch, excited and superstitious, saw the 
saints—George, Demetrius, and Theodosius—descending 
through the clouds of heaven to their support. 
The consummate skill of Shakespeare in portraying the 
different phases of false perception, and his power of 
psychological analysis, are wonderfully illustrated in 
the dagger-scene of Macbeth. Intent on murder, 
with ‘‘ courage screwed to the sticking-place,’’ Macbeth 
is about to enter the king’s chamber, when he is startled 
