UROGENITAL SYSTEM 223 



sexual external manifestations, and internally by sexual stimuli 

 which depend in the female upon the ripening and discharge of 

 the ovum, and in the male upon the formation and storing up 

 of semen. 



These sexual impulses appear in wild animals, both male 

 and female, at definite seasons of the year, known as the "rut 

 season". Among domestic animals the male obeys no rule, 

 because the semen is secreted constantly ; the female, on the 

 contrary, observes definite " rutting seasons," each of which 

 terminates in the ripening and discharge of an ovum. If several 

 ova mature simultaneously, as in multiparous animals, the 

 "rutting time" (" Brunstzeit") and the menstruation ("Brunst- 

 periode ") occur together. The " rutting season " of the mare 

 occurs in spring or autumn, that of the cow in spring and 

 autumn ; in pigs, bitches and cats, two or three times a 

 year. 



DURATION OF EACH MENSTRUAL PERIOD. 



Mare . . 24-48 hours 



Cow . . 1-4 days 



Sheep . . . 1-2 ,, 



Pig i-3 



Bitch . ... 8-10 



In women the ripening of one or two ova associated with 

 discharge of blood takes place regularly as a rule every twenty- 

 five days, so that in a year there are usually thirteen menstrual 

 periods. These periods of three to seven days are almost 

 identical with the " rutting periods " of animals, and terminate 

 generally with stimulation of the sexual impulse, but in women 

 there is nothing corresponding to the actual "rutting season". 

 This is not absolutely peculiar to the human race, for many 

 old-world apes, especially the anthropoids, menstruate in the 

 same manner. Darwin refers to this relation between the 

 periodicity of functions and the phases of the moon : 



" Man is subject, like other mammals, birds, and even insects, 

 to that mysterious law which causes certain normal processes, 

 such as gestation, as well as the maturation and duration of 

 certain diseases, to follow lunar periods." " In the lunar, or 

 weekly, recurrent periods of some of our functions we appar- 



