646 THE DISEASES AND DISORDERS OF THE OX. 



allantoid membrane is directly connected with the bladder of 

 the foetus by means of a tube called the urachus. 

 This tube, together with the blood-vessels connecting the foetus 

 with the chorion and its cotyledons, forms the umbilical-cord or 

 navel-string, which is generally broken during the act of 

 delivery. These blood-vessels are the arteries which convey 

 the impure blood out of the body of the foetus to the cotyledons, 

 and the veins which return it, after it has been reoxy- 

 genated in the manner previously alluded to. 



Due provision is made for an equal distribution of this pure 

 blood through the body of the foetus, so that every part of the 

 frame may be built up at the same time. 



The act of cleansing in the case of the cow generally takes 

 place some hours after the calf is born. If the placental mem- 

 branes, instead of being separated, are retained, they set up a 

 great deal of irritation. They may putrefy, and death may in 

 consequence ensue. Cows, suffering from a depraved appetite, 

 have been known to devour their cleansings, and impaction of 

 the rumen may result therefrom. 



Now, the term oestrum is employed to designate that condition 

 of the female which shows her fitness and desire for the male. 

 It is associated with puberty, and passes off on the approach of 

 old age. In some of our improved breeds of cattle, especially 

 when well kept and attended to, oestrum comes on very early 

 in life, and in such instances the animal often conceives when 

 she is but little more than a year old. These early conceptions, 

 however, too frequently prove injurious, both by interfering 

 with the development of the frame of the female, and also by 

 deteriorating the quality of the offspring. 



Some animals, such as the dog and pig, which in a state of 

 nature produce only one litter a year, will, when domesticated, 

 bring forth several. 



The immediate cause of oestrum is the existence of fully 

 matured ova in the ovaries, and impregnation can only be 

 effected when the ova are in this condition. 



The time occupied in the development of the ova differs in 

 different animals, and hence we observe a variation in their 

 return to the male. Impregnation is produced by the fecundating 

 fluid of the male acting on the matured ovum of the female, 

 which action probably takes place in the ovarium. There is 



