e
females), usually appeared at puberty, and disappeared at about the age
of forty or forty-five years." The second case is that of four
brothers, who when about twelve years old suffered almost every week
from severe headaches, which were relieved only by a recumbent position
in a dark room. Their father, paternal uncles, paternal grandfather,
and paternal granduncles all suffered in the same way from headaches,
which ceased at the age of fifty-four or fifty-five in all those who
lived so long. None of the females of the family were affected.[178]

It is impossible to read the foregoing accounts, and the many others which
have been recorded, of diseases coming on during three or even more
generations, at the same age in several members of the same family,
especially in the case of rare affections in which the coincidence cannot
be attributed to chance, and doubt that there is a strong tendency to
inheritance in disease at corresponding periods of life. When the rule
fails, the disease is apt to come on earlier in the child than in the
parent; the exceptions in the other direction being vey much rarer. Dr.
Lucas[179] alludes to several cases of inherited diseases coming on at an
earlier period. I have already given one striking instance with blindness
during three generations; and Mr. Bowman remarks that this frequently
occurs with cataract. With cancer there seems to be a peculiar liability to
earlier inheritance: Mr. Paget, who has particularly {80} attended to this
subject, and tabulated a large number of cases, informs me that he believes
that in nine cases out of ten the later generation suffers from the disease
at an earlier period than the previous generation. He adds, "In the
instances in which the opposite relation holds, and the members of later
generations have cancer at a later age than their predecessors, I think it
will be found that the non-cancerous parents have lived to extreme old
ages." So that the longevity of a non-affected parent seems to have the
power of determining in the offspring the fatal period; and we thus
apparently get another element of complexity in inheritance.

The facts, showing that with certain diseases the period of inheritance
occasionally or even frequently advances, are important with respect to the
general descent-theory, for they render it in some degree probable that the
same thing would occur with ordinary modifications of structure. The final