From these figures it appears that in the 6,550 cases under consideration, the age 15 was that at which the first appearance of menstruation was most frequently observed, namely in 1,240 instances, or 18.9 per cent. The age 14 comes next, with 1,193 instances, or 18.2 per cent. The case in this series in which menstruation appeared earliest, namely in the ninth year, was observed by Mayer, the girl being a blonde of average height, good family, and German descent; the case in which menstruation appeared latest, namely in the twenty-ninth year, was that of a woman living in Berlin, who was sickly and chlorotic up to the time of her marriage, and in whom menstruation did not appear until some years after that event.

As regards climatic influences, all the data at our disposal prove that the hotter the climate the earlier the menarche. According to Marc d’Espine the age at puberty varies in an almost geometrical ratio with the mean annual temperature.

The dependence of the menarche upon climatic influences is clearly shown by the statistical data collected from various regions of the world. We append the general compilation of Gebhard dealing with this question.

A. Europe.

For Europe the data furnished by Ploss are grouped by Gebhard in the following manner.

1. Northern Europe.

The average age at which menstruation first appears, according to the older statistics, is in Swedish Lapland 18, in Norway, 16.12. In Copenhagen it is 16.75, in St. Petersburg 14.5.

More recent statistics for Finland are furnished by Engström. Among 3,500 women of pure Finnish descent, he found that menstruation began:

At the age of:
8 years in2 instances.
9 years in2 instances.
10 years in4 instances.
11 years in41 instances.
12 years in178 instances.
13 years in458 instances.
14 years in715 instances.
15 years in778 instances.
16 years in614 instances.
17 years in369 instances.
18 years in195 instances.
19 years in91 instances.
20 years in31 instances.
21 years in8 instances.
22 years in10 instances.
23 years in2 instances.
24 years in1 instance.
25 years in0 instance.
26 years in1 instance.

Thus, in nearly half of all Finnish women, menstruation begins with the completion of the fourteenth and fifteenth years. The statistics include women of all classes of society.