There were actual epidemics of insanity affecting masses of the population, as shown in the children's crusade, the Jewish massacres and the dancing mania in the Rhine provinces.

Where civilization seems to be the highest, statistics show the most insane, but this most probably depends upon better recognition of the condition and better provision for asylum care.
The so-called functional diseases have a close relation with diseases of the nervous system, for they chiefly concern the reactions of nerve tissue.

Disease expressing itself in disturbance of function only, does not seem to fit in with the conceptions of disease which have been expressed, nor can we imagine a disturbance of function which does not depend upon a change of material.

Living matter does not differ intrinsically from any other sort of matter; like other matter its reactions depend upon its composition structure[1] and the character of the action exerted upon it.

By functional disease there is expressed merely that no anatomical or chemical change is discoverable in the material which gives the unusual reaction.