of disease there can be change at any place along the line, in the sense organs, in the conducting paths or in the central organ.  Thus there may be false visual impressions which may be due to changes in the retina or in the optic nerve or in the brain matter to which the nerve is distributed.  It is perfectly possible that substances of an unusual character or an excess or deficiency of usual substances in the fluids around brain cells may so change them that such unusual reactions appear.  There may be, of course, very marked individual susceptibility, which may be congenital or acquired.  The perception of every stimulus involves activity of the nerve cells, and it is possible that the constant repetition of stimuli of an ordinary character may produce sufficient change to give rise to unusual reactions, and this particularly when there is lack of the restoration which repose and sleep bring.  We know into what a condition one’s nervous system may be thrown by the incessant noise attending the erection of a building in the vicinity of one’s house or the pounding of a plumber working within the house, this being accentuated in the latter case by the thought of impending financial disaster.  Even the confused and disagreeable sound due to the clatter of high-pitched women’s voices at teas and receptions may, when frequently repeated, be productive of changes in the nerve cells sufficiently marked to give rise to the unusual reactions which are evidence of disease.

In the condition known as neurasthenia, which is often taken as a type of a functional disease, the basal and intrinsic cause is activity of the nervous system with the using up of material which is not compensated for by the renewal which comes in repose and sleep.  Neurasthenia is one of the common conditions of our civilization, found among children and adults, the poor and rich, the idle and the factory worker; it is rife in the scholastic professions and among those who earn their living by brain work.  It seems to be more common in the upper classes and particularly in the women, but this is because these are more subject to medical care and the condition is more in evidence.  There are all sorts of symptoms attached to the condition, for the unusual mental action can be variously expressed.  The cerebral form has been thus described by a well-known medical writer:  “One of the most characteristic features of cerebral neurasthenia is a weary brain.  The sensation is familiar enough to any fagged man, especially if he fall short of sleep.  Impressions seem to go half into one’s head and there sink into a woolly bed and die.  Voices sound far off, the lines of a book run into one another and the meaning of them passes unperceived.  Doors bang and windows rattle as they never did before; if a shoestring breaks, an imprecation is upon the lips.  Business matters are in a conspiracy to go wrong.  Letters are left unopened partly from want of will, partly from a senseless dread lest they contain bad news.