THE URINARY SYSTEM 433 



760.— The foetus is connected with the placenta by means of the 

 umbilical cord, or navel string (Plate XLII. t No. 4), which is made 

 up of — 



1. The Umbilical Vein, carrying pure blood from the placenta 



to the foetus. 



2. Two Umbilical Arteries, conveying venous blood back to 



the foetal membranes. 



3. The Urachus, a tube which connects the allantois with the 



bladder. 



The blood of the mother does not circulate in the body of the foetus 

 directly, the offspring being nourished by the aid of the villi on the 

 outer coat of the placenta, which absorb nutrient material from the 

 blood of the parent supplied to the womb. 



761. Abortion, Slinking, Slipping, or Casting the Calf.— Of 



all the diseases that infest the stock of the farm and fold, that of 

 abortion may be looked upon as the most serious. This malady has 

 been known from time immemorial, reference being made to it in 

 Biblical history, for, according to Gen. xxxi. 38, Jacob seems to 

 have known the secret of its prevention ; it is, therefore, a great 

 pity he did not leave it behind him for our benefit in these latter days. 

 Abortion, however, is not very common in the mare, and when it 

 does occur it is generally the result of an accident. Sheep are more 

 susceptible to its baneful influence, but nothing to the same extent as 

 COWS, among which the causes of abortion are numerous. A solitary 

 case may occur from some injury, such as the animal being caught in 

 a gate or doorway, or by a goad from another beast ; from indigestion 

 and distension of the stomach with gas, causing pressure on the gravid 

 uterus, and displacement of some of the placental attachments ; from 

 urticaria and specific diseases, such as ' foot and mouth ' disease ; also 

 from bleeding, the administration of poisonous drugs, etc. 



762. When the complaint rages in the epizootic form, and attacks 

 stock on various farms for miles around, it is then that its baneful 

 effect is most bitterly felt. Most of the abortion outbreaks that have 

 occurred in my district have been cases where a farmer changed his 

 holding, sold off his cattle, and then purchased from other farm sales 



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