38 THE HOKSE BOOK. 



observe, nevertheless, that there is no actual 

 blood transmission directly from the dam to 

 the fetus — there is no direct communication be- 

 tween the maternal and fetal circulations. In- 

 stead the blood vessels of the placental mem- 

 branes (which we recognize as the afterbirth 

 after foaling) lie contiguous to the blood ves- 

 sels of the dam and sustenance is afforded to 

 the fetus by diffusion. Besides this there is 

 in the amnion or water bag a large supply of 

 fluid which is freely imbibed and absorbed by 

 the foal. It is thus easy to see how a very 

 slight disturbance of the juxta-position of the 

 blood vessels of the dam and membranes, or of 

 the organs secreting the water in the amnion, 

 may cause nourishment to be shut off and a 

 weak or dead foal be produced. The merest 

 disarrangement of the contiguity of the blood 

 vessels may work harm to the young and in 

 this way many a weakly ill-nourished anemic 

 foal may be accounted for when the owner 

 could see no reason why it should not have come 

 all right. 



In order for a mare to conceive it is neces- 

 sary for the sperm-cells to enter the cavity of 

 the womb and the Fallopian tubes. As they are 

 microscopic in size they are necessarily very 

 delicate in structure. It is plain that if the 

 neck of the womb is absolutely closed they can 

 not enter. After impregnation has taken place 

 and the fertilized agg has descended into the 



