In other countries persons having children beyond their ability to support were privileged to sell them to citizens, who contracted to raise them on condition that they became their slaves. General Law, and the Influence of War.--In the increase of the world's population, although circumstances may for the time alter it, a general average of prolificity has, in the long run, been maintained. In the history of every nation artificial circumstances, such as fashion, war, poverty, etc., at some period have temporarily lowered the average of prolificity; but a further search finds another period, under opposite circumstances, which will more than compensate for it. The effect of a long-continued war or wars on generation and prolificity has never been given proper consideration. In such times marriages become much less frequent; the husbands are separated from their wives for long periods; many women are left widows; the females become in excess of the males; the excitement of the times overtops the desire for sexual intercourse, or, if there is the same desire, the unprolific prostitute furnishes the satisfaction; and such facts as these, coupled with many similar ones, soon produce an astonishing effect upon the comparative birth-rate and death-rate of the country. The resources of a country, so far as concerns population, become less as the period of peace-disturbance is prolonged. Mayo-Smith quotes von Mayr in the following example of the influence of the war of 1870-71 on the birth-rate in Bavaria,--the figures for births are thrown back nine months, so as to show the time of conception: Before the war under normal conception the number of births was about 16,000 per month. During the war it sank to about 2000 per month. Immediately on the cessation of hostilities it arose to its former number, while the actual return of the troops brought an increase of 2000 per month. The maximum was reached in March, 1872, when it was 18,450. The war of 1866 seems to have passed over Germany without any great influence, the birth-rate in 1865 being 39.2; in 1866, 39.4; in 1867, 38.3; in 1868, 38.4. On the other hand, while the birth-rate in 1870 was 40.1, in 1871 it was only 35.9; in 1872 it recovered to 41.1, and remained above 41 down to 1878. Von Mayr believes the war had a depressing influence upon the rate apart from the mere absence of the men, as shown in the fact that immediately upon the cessation of hostilities it recovered in Bavaria, although it was several months before the return of the troops.