MATURATIOX OF THE <iRAAFIAX VESICLES. 63 



marked influence on the "rut," in hastening its development and its 

 periodicity ; but the economical law to which it is subordinate does 

 not vary. With many species, the rut only appears once a year ; while 

 in others wliich are favourably placed with rof^ard to alimentation, it 

 persists in every season, or at least during a large part of the year. 

 Domesticity, iu assuring animals food and shelter, and removing them 

 from the risks and alternations of an erratic life, multiplies the periodical 

 returns of this condition. Fowls, Pigeons, etc., lay despite the rigours 

 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 impregna- 

 tion may and does occur soon after parturition. The Cow, Ass, and 

 Sheep, and, it is believed, the Mare, will copulate with gi-eater certainty 

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



As has been just stated, various conditions intluence the appearance of 

 this state, and more or less change the period and the intervals of its 

 advent. Warmth, shelter from vicissitudes of weather, an abun- 

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

 labour, favour 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 un- 

 favourable. It renders Mares and Cows less serviceable, and even 

 dangerous, constituting the disturbance designated " nymphomania." 

 Repeated intercourse with the male will not allay the abnormal con- 

 dition, but frequently aggravates it. Such animals will not breed. 

 Ovariotomy is often practised for " nymphomania," and in the Cow the 

 operation is frequently followed by subsidence of the troublesome 

 symptoms for a time ; in the Mare it is much less successful. 



SECTION III.— MATURATIOX OF THE (IKAAFIAN VESICLES. 



The spontaneous and periodic ripening and dehiscence, or discharge, 

 of the ovarian vesicle that marks the period of cestrum in the domesti- 

 cated animals, though independent of fecundation, yet is doubtless 

 intended to conmience the act of generation. The peculiar condition 

 which accompanies 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 tlie 

 ovaries. A certain Ciraatian vesicle or vesicles, according to the species 

 and whether the animal is uniparous or multiparous, becomes more 

 voluminous than the others, raising 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 bloodvessels 

 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. 28, a) 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 



