WILLIAM G. STEVENSON. 67 
thought has been despoiled of its most precious adorn- 
ment, and in the place where once the Muses sat, mock- 
ing echoes now hold carnival, and ‘‘ melancholy sits on 
brood.”’ 
To give a definition of insanity which shall prove ac- 
ceptable to medical psychology and to practical juris- 
prudence, is a more difficult task than it may appear. 
This comes because of the differences in the appreciation 
of causes and effects in mental phenomena which exist 
between minds trained in the technical details of physi- 
ological and pathological knowledge, and those who 
witness merely a few of the more pronounced express- 
ions of lunacy, but are unable to trace the expressions 
to their relating causes. 
To have even a moderate understanding of insanity, it 
is necessary to clearly comprehend the nature and im- 
port of ‘‘illusion,’’ ‘‘ hallucination,’ and ‘‘ delusion’? — 
which, when they exist, are of so much importance that 
some would fain have us believe that the possession of 
any one of these symptoms is sufficient to make genius 
and insanity ‘‘a little more than kin, and less than 
kind.”’ 
When a person sees, hears, smells, tastes, or feels an 
object, but perceives it to be what it is not—as when a 
tree becomes a man, and the murmuring wind his voice 
—an illusion exists ; a real sense-impression is wrongly 
interpreted by the perceptive centers, and hence. the 
perception does not correspond with the external object. 
Hallucination originates within the brain, and is the 
perception of that which has no real existence ; indeed, 
so purely subjective is it, that the senses have no 
agency in its production. Under conditions of concen- 
trated attention, ideas, feelings, and sense-perceptions, 
are marshaled into consciousness with as great distinct- 
ness as if they were the products of external objects, 
rather than of subjective conditions alone. This comes 
