Of the existence of a tendency to disease transmitted from parents to offspring no doubt can be entertained; whether the predisposition so conveyed be called idiosyncrasy, constitutional peculiarity, remarkable liability, or special receptivity, or be designated by any other form of words, the fact remains that the influence of heredity has always been recognized, although the term itself may not have been used by the older writers. It may be defined as the law of inheritance not necessarily limited to the transmission of a tendency to disease, but applying equally to everything which belongs to the living organism, every quality, indeed, whether good or bad, whether relating to mental functions or to organic structure. A modification in the character of organs due to the manner of their employment in a former generation has often been observed; thus large hands are inherited by people whose ancestors led laborious lives, while small hands belong to the descendants of those who have not been compelled to follow occupations which require manual work. In the course of the observations made by Darwin many instances are mentioned of the appearance of peculiarity of structure and of certain diseases at particular periods of life in certain families, and among the cases quoted are blindness occurring in a family and being transmitted to twenty-seven children and grandchildren, the affection beginning always between the fifteenth and sixteenth year, and ending in a total loss of sight at the age of twenty-two. Also of insanity in a family affecting grandfather, father, and son, who all became insane and committed suicide at the age of fifty; in fact, the evidence offered by biologists in favour-of the remarkable influence of heredity in continuing a tendency to certain diseases is so complete that it is impossible to question the fact, It is indeed perfectly well known that scrofula, asthma, rheumatism, gout, epilepsy, blindness, and deafness run in families - not necessarily in one continuous line, but commonly interrupted, even a whole generation being passed over, the disease appearing in the next.