From what has gone before we have seen that minute differences in local structure are the usual subjects of inheritance. Coming to more considerable differences in structure, such as constitute more or less definite divergences from the normal, it is not surprising to find that they also are inherited.

A common structural peculiarity is webbing of the fingers or toes, and this. comparatively slight divergence is very distinctly matter of inheritance. The author knows of a case in which the second and third toes of both feet are imperfectly separated, so that, although the bones are complete, the toes are united nearly to their tips by webs of skin. This peculiarity was by a man transmitted to his son, who died in boyhood, to a grandson, the child of one of his daughters, and, although in a diminishing degree, to several great-grandchildren. Sedgwick, in his very elaborate series of papers in the Medico-Chirurgical Review for 1861 and 1863, adduces many cases of inheritance of supernumerary digits, crooked fingers, cleft iris, squinting, etc. He gives, for instance, a case in which a supernumerary finger was attached to,the outer side of the first phalanx of the little finger. The deformity had occurred for five generations, and the person under observation was the fourth child of a family, all of whom except the second were born with this deformity.

There is also the well-established inheritance of Ichthyosis, the most striking instance of which is that shown by the family of Lamberts, the so-called "Porcupine family," adduced by Darwin in his "Animals and Plants under Domestication." In the original Lambert the skin was covered by warty projections which were periodically moulted. He had six sons and two grandsons similarly affected, and it is remarkable that the inheritance was confined to the male sex, the two grandsons having seven sisters who were free from the malady. A still more striking instance of the inheritance of ichthyosis is related by Sedgwick. The disease was observed in a boy fourteen years of age, and on tracing his family history it was found that he derived it from his grandfather. This man had been affected with the disease, and it is a striking example of atavism or latency in one generation that none of his children showed the disease, although there were three sons and three daughters, while of seven grandchildren (five males and two females) four of the males were affected and none of the females. The affected males were the children of daughters of the original case.

Haemophilia or hemorrhagic diathesis depends on an unknown structural peculiarity either in the blood or vessels, by virtue of which bleeding readily occurs, and when it takes place is stopped with difficulty. This condition is in the highest degree inherited, and it is so in the peculiar manner illustrated by Sedgwick's cases of Ichthyosis mentioned above. Many cases have been traced in their connections, and it appears that it is never directly transmitted. It occurs almost alone in the male sex, and a person affected does not transmit it to his own sons but to those of his daughters. It always in this way misses a generation, and appears in the grandsons of the person transmitting.

Daltonism or Colour-blindness is also demonstrably inherited, and it is usually transmitted in the same peculiar fashion as haemophilia. In nine-tenths of the case Daltonism occurs in the male sex, and it is usually transmitted to the grandsons of the original case through his daughters. (Sedgwick, Wickham Legg).

Diabetes insipidus is another condition, which is apparently inherited in a remarkable degree. In this affection the person drinks excessively and passes a large excess of urine. We may presumably infer that the kidneys are unduly large, and we know that the bladder is unusually capacious. This was proved in a case recorded by Dr. Fiidayson, and was also determined by Weil in the cases to be presently mentioned.

Gee has recorded cases showing that this condition is hereditary, and Weil records a most remarkable instance of its inheritance. Weil met with a case, and he set himself, by hunting up and down the country, to find all about the relatives of his patient, with the result of producing a most elaborate genealogical history of the family. He traced ninety members of the family extending through four generations, seventy of whom were living at the time of the observation. He personally investigated most of these seventy cases. The disease was traced to a man called Johann Peter Schwartz, who was the common ancestor of the family, and was born in the year 1772. His descendants were five children, twenty-nine grandchildren, and fifty-six great-grandchildren, in all ninety-one persons. Of these no less than twenty-three were certainly diabetic, and thirteen.doubtfully so. Omitting the doubtful cases altogether, there remain seventy-eight persons, of whom twenty-three were affected, or thirty per cent. According to Weil this condition was perfectly consistent with good health. They were evidently prolific enough and generally long livers. The original Schwartz lived to be eighty-three, and of his three daughters one died at seventy-four, and the other two were still alive at the time of observation, being respectively seventy-six and sixty-seven years of age.

The facts hitherto adduced suffice to show that, in accordance with what we find in regard to normal differences in structure, abnormal peculiarities in structure or function are also subject to inheritance. It now remains to show on a similar basis of fact that susceptibilities to disease are also matters of inheritance, and that the varying susceptibilities of different persons depend on peculiarities, which cannot be, perhaps, demonstrated like those given above, but which frequently coexist at least with definite peculiarities of structure.