PHYSIOLOGY. 29 



The temper becomes altered. It occasionally happens 

 that Mares which are vicious at any other period, are 

 perfectly quiet at this ; while others again are very 

 troublesome when in this condition. 



Certain changes also take place in the ovaries. 

 These organs become congested and considerably 

 enlarged. One or more Graafian vesicles become fully 

 developed, find their way to the surface of the ovary, 

 and when there, rupture, their contents escaping into 

 the Fallopian tubes. In animals which give birth to 

 only one at a . time, only one Graafian vesicle is 

 ruptured, and that generally in the right ovary ; but in 

 those that have several young at a birth, two or more 

 vesicles are ruptured, the rupture taking place from 

 right and left alternately. When these changes in the 

 female are going on and an ovum has been liberated, 

 if no contact with the male is allowed, impregnation 

 can not take place (except as before stated), and the 

 various organs resume their normal condition, and 

 remain so for a time, which varies in the different 

 animals. 



In the Cow, the period of cestrum Is present from 

 •one to four days, and then disappears, to reappear in 

 from twenty-one to twenty-two days. In the Mare, the 

 period lasts from three to six days, and disappears, to 

 return again in from twenty-one to twenty-two days. 



The Bitch is in heat generally twice a year, in 

 ■early spring and autumn, and the period lasts from 

 ■eight to fifteen days. 



In Great Britain, the Sheep appears in heat about 

 the middle of September, the condition lasting for 



