That such minds are most frequently to be met with in an age of ignorance, we should naturally suppose, and we are borne out in that supposition by the fact, that these diseases have been declining in proportion to the advance of knowledge; but credulity and enthusiasm are not incompatible with a high degree of civilization: and if, among the educated classes, the female sex is more sentimental than the male, and the affluent are more credulous than those who are dependent on their own exertions for their support, it is to be accounted for by the fact, that they usually devote more leisure to the pleasurable contemplation of works of imagination, and are less imperatively called on to improve their judgment by the dry study of facts, and the experience acquired in the serious business of life. But there is no class, even in this age of boasted reason, wholly exempt from the baneful influence of fanaticism; and instances are not wanting, in our own days, and in this very capital, to prove, that disorders (how can we more charitably designate them?) much resembling some of those described in the following pages, may make their appearance among people who have had all the advantages of an enlightened education, and every opportunity of enlarging their minds by a free intercourse with refined society. I thus venture to hope, that by bestowing a leisure hour on this small portion of medical history, the physician may enlarge his knowledge of disease, and the moralist may gather a hint for the intellectual improvement of his fellow-men. The author has, however, a more extended object in view—the histories of particular epidemics are with him but the data from which we are to deduce the general laws that govern human health in the aggregate. Whether there be such an _entity_ as collective organic life, and whether, as a consequence, there exist general laws which regulate its healthy or morbid condition, I do not here undertake to determine; but the notion is peculiar, and in order that it may be more fully exposed to the reader, I have translated as an introduction to the present volume[203], an Appeal which Dr. Hecker has made to the medical profession of his own country for assistance in his undertaking. If, in the course of the remarks contained in this address, he has been somewhat severe in his censure of the neglect, both in this country and in France, of the study of Medical History, I freely confess myself to be one of those who are more anxious to profit by his castigation than to dispute its justice.