156 On Light in some of its Relations to Disease. 



variations, may be met with almost daily in the practice of 

 many physicians. A gentleman from a neighboring city 

 has always suffered from a general nervous irritability ; he 

 has been one of the class of excessively nervous people ; 

 his grandfather had always a great deal of neuralgia; but 

 his father, who observed very strict habits of life, and 

 whose occupation kept him much in the open air, had no 

 nervous trouble. Three brothers have suffered terribly 

 from neuralgia, and one, who for many years was subject 

 to functional nerve-troubles, has now an organic disease 

 of the nervous centres. He has one sister, who is subject 

 to oft-repeated nervous headaches. 



Great attention has been paid to this predisposing ten- 

 dency, both hereditary and spontaneous, by many of the 

 most learned members of the medical profession; but, 

 unless the hypothesis which I present to-night explains 

 this peculiar and unfortunate tendency which forms the 

 unwelcome inheritance of so many families, nothing has 

 ever been known of it except its existence. 



There is a peculiarity about this predisposing tendency 

 which should be noted in passing — that persons affected 

 with one form of functional nervous disturbance at one 

 period of life, are liable to suffei; from some other form at 

 a later period. Thus, one who in childhood suffers from 

 chorea (St. Vitus's dance), will generally, in later life, be 

 the subject of severe recurring headaches, of neuralgia, or 

 perhaps of epilepsy. It is a commonly-observed fact with 

 physicians that hysterical girls usually become nervous 

 women, subject to periodical headaches. 



From such facts as these we may logically conclude that 

 the predisposing cause of this class of troubles is a per- 

 manent one, that it often descends from parent to child, 

 and that it is usually the same in different persons, and for 

 different forms of functional nervous diseases. 



About five years ago my attention was drawn to a sin- 



