876 THE PHYSIOLOGY OF REPRODUCTION. 



lasts, as a rule, for several days, and in the female is accompanied 

 by changes which resemble those of menstruation. The external 

 genital organs become swollen and in many animals there, is a 

 discharge of mucus or mucus and blood from the uterus. His- 

 tologically the mucous membrane of the uterus undergoes changes 

 similar to those of menstruation that is, the membrane increases 

 in size and becomes congested with blood and it exhibits a phase 

 of degeneration during which some of the epithelial lining may be 

 cast off and some hemorrhage occur. As in the case of the men- 

 strual period, the heat period or oestrous cycle may be divided into 

 four subperiods (Marshall and Jolly) : the procestrum, during which 

 the genital organs are congested and bleeding occurs, corresponds 

 with menstruation; the oestrus, the period of sexual desire; the 

 metcestrum, the period of repair and return to normal conditions, 

 and the ancestrum, the period of rest. If sexual union is prevented 

 during this period heat passes away in a few days, but recurs again 

 at intervals which vary in the different mammals: 4 weeks in the 

 monkey, mare, etc.; 3 to 4 weeks in the cow; 2 to 4 weeks in the 

 sheep; 9 to 18 days in the sow; 12 to 16 weeks in the bitch, etc. 

 The recurrence of the period under these circumstances suggests 

 at once the essential resemblance to the monthly periods of women. 

 According to Heape's most interesting observations upon monkeys 

 (Semnopithecus),* some of these animals show a regular monthly 

 flow lasting for 4 days, except when conception takes place. The 

 changes during heat must be considered as physiologically ho- 

 mologous to those of menstruation. The sexual excitement that 

 attends the condition in the lower animals is not distinctly repre- 

 sented in man, although it is commonly said that in the period pre- 

 ceding or following menstruation the sexual desire is stronger than 

 at other times, but in the changes undergone by the uterus and the 

 fact that these changes are connected, as a rule, with the liberation 

 of an egg from the ovary (ovulation), the two phenomena are 

 physiologically similar. 



Relation of the Ovaries to Menstruation. It appears to be 

 clearly demonstrated that the phenomenon of menstruation is de- 

 pendent upon a periodical activity in the ovaries. When the 

 ovaries are completely removed menstruation ceases (artificial 

 menopause) and the uterus undergoes atrophy. When the ovaries 

 are congenitally lacking or rudimentary, a condition of amenorrhea 

 also exists. These facts and the connection of the ovaries with 

 menstruation are further corroborated in a striking way by experi- 

 ments upon transplantation or grafting of the ovary. This experi- 

 ment has been performed upon lower animals (apes) as well as upon 



*Heape, "Philosophical Transactions, Royal Society," 185 (B), 1894, 

 and 188 (B), 1897. 



