

CHAP. XXXIX.] HEAT AND HUT IN ANIMALS. 563 



becomes very great, or the ova are perfectly developed and capable 

 of being impregnated. At this time, the stroma of the ovary is seen 

 to be everywhere studded with ovisacs in various stages of develop- 

 ment; the largest and most mature occupying the peripheral parts 

 of the organ, while those containing mature ova, which are about 

 to be discharged, form considerable prominences, projecting from 

 the surface of the ovary."^ 



The discharge of ova from the ovary in animals, as in the human 

 subject, occurs only at certain definite periods, which vary much 

 in different animals. It is only at these times that the female 

 animal will receive the male, and that the aptitude for conception 

 exists. At such a time the animal is said to be " in heat " or 

 " rut." In the bitch, this period occurs twice in the year, and 

 lasts for about a fortnight each time; in the sheep and in the 

 cow, and in domestic animals generally, it occurs much oftener than 

 in wild animals, and the periods of recurrence are not definite. 



If the ovary of an animal be examined at the time of " heat/' 

 it will be found turgid with blood, and several Graafian vesicles 

 will be seen projecting from its surface, forming prominences, 

 the most superficial portions of which appear quite thin, and 

 almost ready to rupture and permit the escape of the contents 

 of the follicle. At the same time, a more abundant secretion of 

 mucus takes place from the walls of the vagina and contiguous 

 parts. In a few instances, also, a bloody discharge has been 

 detected in the vagina ; but it must be distinctly borne in mind, 

 that this is not a constant phenomenon. It only occurs in small 

 quantity, and it never appears at each successive period of heat, 

 while it is always accompanied with increased sexual desire. 



It may be considered as established, that in the human female, 

 at or about the period of menstruation, a discharge of ova takes 

 place; and at these times the ovaries are extremely turgid, and 

 their vascularity is much increased. From very numerous observa- 

 tions, it has been distinctly proved, that conception is more likely 

 to take place a few days after menstruation than at any other 

 period, a fact which has led Naegele to fix the period of delivery at 

 nine months and eight days after the last menstrual discharge ; 

 while, in few instances, the ovum has actually been seen within 

 a very short time after its escape from the Graafian follicle. 



From these facts, most physiologists have been led to look upon 



* Dr. Barry calculates, that in the ovary of the cow about the period of 

 puberty, there are as many as two hundred millions, corresponding to a 

 cubic inch of the stroma. 



