6o OBSTETRICAL PHYSIOLOGY. 



Fowls, Pigeons, etc., lay despite the rigors of winter, and the domesticated 

 mammals are in heat at short intervals. 



Though, as a rule, oestrum does not appear until after parturition is 

 achieved, and lactation has nearly or quite ceased, yet it is not rare to find 

 some animals, as the Mare and Pig, manifest a desire for the male, and 

 even copulate ; and it is no less a fact that rutting and impregnation may, 

 and does occur, soon after parturition. The Cow, Ass, and Sheep, and, 

 it is believed, the Mare, will copulate with a greater certainty of success 

 on the ninth day after parturition than at any other time. 



It must be remembered that various conditions influence the appear- 

 ance of this function, and more or less change the period and the intervals 

 of its advent. Warmth, shelter from vicissitudes of weather, an abundance 

 of nourishment, especially that of a stimulating nature, and easy labor, 

 favor its more frequent and early appearance, and especially a judicious 

 bringing together of the male and female. It has also been induced by 

 the injection of certain substances into the vagina. 



The persistence of this condition for longer than the natural period is 

 a symptom of uterine or ovarian derangement, and therefore unfavorable. 

 It renders the animals of less value, or even dangerous, constituting the 

 disturbance designated " nymphomania." 



SECTION III. MATURATION OF THE GRAAFIAN VESICLES. 



The spontaneous and periodic ripening and dehiscence, or discharge, 

 of the ovarian vesicle that marks the period of oestrum in the domesticated 

 animals, though independent of fecundation, yet is doubtless intended to 

 commence the act of generation. The peculiar condition which accom- 

 panies the maturation of the ovum, the intense desire of the female for the 

 male, and the excitation produced in the latter at this period, with its 

 aptitude for procreation, conclusively demonstrates this. At this time, as 

 we have seen, particular changes occur in the ovaries. A certain Graafian 

 vesicle or vesicles, according to the species and whether the animal is 

 uniparous or multiparous, becomes more voluminous than the others, 

 raises the enveloping membrane of that body, and makes a more or 

 less salient projection on its surface, as is witnessed in the ovary of the 

 Pig. Around this vesicle the blood-vessels enlarge, and the stroma 

 is congested ; while in its interior an effusion of blood takes place ; the 

 capsule becomes greatly distended and injected, and at a particular point 

 gives way, leaving an irregular gap through which the ovum (Fig. 21, <^) 

 escapes. In the Pig, during the evolution of the vesicle, the corpus 

 luteum is red, deep red, blue, or nearly black. It is probable that the 

 Graafian vesicles open at any part of the surface of the ovary, in those 

 animals in which the pavilion of the Fallopian tube is large enough to 

 envelop it more or less completely. But in those creatures, such as the 

 Mare, in which the ovary is so voluminous, the pavilion cannot cover it ; 

 and it is not at all unlikely that in this case the rupture of the vesicles 

 occurs at the hilus of the ovary, as the corpora lutea have only been 

 observed at this part. In multiparous animals, the rupture of the vesicles 

 at one period of rutting does not appear to take place simultaneously, but 

 successively. 



The number of Graafian vesicles which come to maturity and rupture 

 at each period of oestrum, depends, with some exceptions, upon the num- 

 ber of young each female brings forth at a birth. The Mare, Cow, and 



