EEPBODUCTIVE FUNCTIONS. 911 



At the occurrence of puberty various changes take place which mark 

 the appearance of reproduetiveness. As such may be mentioned in- 

 creased vascularity and development of the external and internal Gener- 

 ative organs, the characteristic changes which now commence in the 

 pelvis, the development of the mammre, and the growth of hair on the 

 pubes and in the axilla. Menstruation recurs, usually, at intervals of 

 twent3'-eight days, and each menstrual period corresponds with the ripen- 

 ing and rupture of a Graafian follicle. During menstruation from one 

 hundred to two hundred grammes of blood escape. This blood has lost 

 its power of coagulation, probably through mixture with the alkaline 

 secretions of the uterus and vagina. The source of the hemorrhage is 

 the mucous membrane lining the uterus. The ciliated epithelium of the 

 uterus becomes swollen, congested, and soft, and almost entirely shed. 

 A similar congestion likewise occurs in the ovaries and Fallopian tubes, 

 the congestion of the ovary leading to a greater transudation of fluid 

 into the Graafian follicle and consequent rupture, while the great conges- 

 tion and engorgement of the blood-vessels of the uterus lead to the 

 rupture of the finer capillaries and the consequent escape of blood. 



In addition to the congestion of the internal genital organs, the 

 external genital organs also become more strongly congested and 

 swollen. * 



Phenomena analogous to the process of menstruation in the human 

 female occur in all females of the class of mammals, in the domestic animals 

 the condition being spoken of as heat, and its first occurrence marks not 

 only the first appearance of the power of procreation but also the times 

 at which copulation with the male will be permitted. In all of the 

 domestic animals the occurrence of heat coincides with the rupture of 

 one or more Graafian follicles -and the escape of one or more ova from 

 the ovary, together with the increased vascularity of the genitals. The 

 external signs of heat are the following: Slight swelling and reddening 

 of the vagina and vulva, more or less flow of mucous, reddish discharge 

 from the genitals, characterized by a peculiar odor, which especially seems 

 to possess the power of attracting the male, frequent urination, often 

 slight swelling of the mammary gland with alteration in the characters 

 of the milk ; the disposition of the animal becomes restless, it seeks the 

 male of the same species, frequently gives vent to various cries, and 

 sometimes refuses to eat. The characteristics of heat vary somewhat 

 in different animals. In the mare urination is frequent, the vulva is the 

 seat of spasmodic discharge, and the clitoris becomes erect. The mare 

 whinnies and seeks the male. Occasionally a small amount of blood 

 escapes from the external genitals. The cow becomes very restless, con- 

 tinually bellows, and attempts to mount other animals even of the same 

 sex. In sheep the appearances of heat are less characteristic, and are 



