Note I — Chapter VIII · THE FUNCTIONS OF THE FEMALE GENITAL ORGANS

Another reason why menstruation is so rarely observed among animals is their posture. If the preparations preceding menstruation are for the purpose of ingrafting the fertilized ovum, it follows that menstruation must occur in all those animals in which the fertilized egg is fully developed to complete maturity within the interior of the mother. This is indeed what happens. All animals with so intimate an attachment of the foetal and maternal organisms that the foetal placenta cannot be detached from the mother without a haemorrhage, show the phenomenon of menstruation.

Menstruation was formerly regarded as the exclusive prerogative of woman, but we know now that woman shares the privilege with many animals. All warm-blooded animals that stand or walk erect, without exception, menstruate. The appearance of the discharge is simply due to posture. The process is going on in all quadrupeds, as the sheep, the cow, the dog, the cat, etc., but on account of the position of the uterus (in quadrupeds the fundus of the uterus is situated lower than the neck) the blood is usually retained in that organ, reabsorbed through the lymphatics into the blood, and consumed in the vital process or eliminated through excretory glands.

In some animals the discharge consists of mucus. In dogs the writer saw real blood. It is only a play of nature, that in one species the congestion of the genitals manifests itself by a sweating of viscous mucus, in the other by a flow of blood.

Even the lower animals shed the same degenerated material. They menstruate through the lymphatics, if for one cause or another impregnation has been prevented. But as a rule, in animals, living in freedom, impregnation always follows the preparation of the uterus, and the phenomenon of menstruation fails to appear. It is only among domesticated animals that the discharge from the genitals is sometimes observed.