D. Hp]RON 
359 
Figs. 1 and 2*. Here the horizontal scale represents the age of onset in 5-year 
groups — the vertical scale the percentages of cases occurring in each age group. 
TABLE I. 
Percentages of Gases whose First Attack of Insanity occiirred 
within Various Age-periods. 
Age-periods 
Father 
Offspring 
Mother 
Offspring 
Percent. 
Per cent. 
Per cent. 
Per cent. 
Under '20 
years 
1-4 
26-2 
0-6 
27 
8 
20—24 years... 
25—29 „ 
0- 4 
1- 4 
18-0 
18-0 
3- 4 
4- 4 
15 
18 
7 
2 
j- Adolescence 
SO— 34 
r 
9-6 
13-0 
7-8 
13 
4 
35—39 
J? 
11 -.5 
7-3 
9-2 
10 
0 
40-44 
9-2 
6-4 
10-3 
5 
8 
45—49 
); 
14-3 
6-0 
12-0 
3 
7 
1 Involutional 
50—54 
)i 
17-5 
0-9 
12-3 
2 
4 
/ jjeriod 
55—59 
13-8 
3-7 
14-0 
1 
7 
60—64 
I) 
10-1 
11-6 
1 
3 
65—69 
„ 
5-0 
8-8 
70—74 
4-6 
0-4 
3-1 
75—79 
)i 
0-4 
1-3 
80 
?> 
0-4 
0-6 
I have been obliged to follow Dr Mott in treating the " under 20 " group as a 
5-year group as otherwise my diagrams would bear no resemblance to his, but this 
procedure is far from satisfactory when such a large proportion of the cases in this 
group are congenital cases in which the age of onset should be taken at 0 years. 
The tables and diagrams show that among the parents more than half the cases 
occur after the age of 50, while among the offspring, more than half occur before 
30, and this is taken to prove that thei'e is Anticipation or Antedating in 
Insanity. 
This will perhaps be made more evident if the percentages of those who became 
insane before the age of 25 are given in each case. Among the fathers, 2°/^ and 
among the mothers, 4<°/^ became insane before the age of 25. Among the off- 
spring, on the other hand, the percentage is 44. Another way of looking at the 
matter is to take the average age of onset of insanity in each case. Dr Mott 
gives a Table showing these averages but unfortunately has omitted the congenital 
cases so that the extent of anticipation is considerably under-estimated, and the 
form in which the data are given does not permit of an accurate calculation of the 
actual averages. From the information given it appears, however, that the average 
age at onset of insanity among the parents is about 50 years, among the offspring 
about 26 years, showing an anticipation or antedating of some 24 years. 
* I am very grateful to Miss H. Gertrude Jones, the Hon. Secretary of the Galton Laboratory, for 
the diagrams which illustrate this lecture. 
46—2 
