THE PLACENTA. 



757 



of strychnia into the abdominal cavity of one foetus, and 

 into the thoracic cavity of another, and then replaced all 

 the parts, every precaution being taken to prevent escape 

 of the poison. In less than half an hour, the bitch died 

 from tetanic spasms ; the foetuses operated on were also 

 found dead, while the others were alive and active. The 

 experiments, repeated on other animals with like results, 

 leave no doubt of the rapid and direct transmission of 

 matter from the foetus to the mother, through the blood of 

 the placenta. 



The placenta, therefore, of the human subject is com- 

 posed of a foetal part and a maternal part, the term, 

 placenta, properly including all that entanglement of foetal 

 villi and maternal sinuses, by means of which the blood 

 of the foetus is enriched and purified after the fashion 

 necessary for the proper growth and development of those 

 parts which it is destined to nourish. 



The whole of this structure is not, as might be imagined, 

 thrown off immediately after birth. The greater part, 

 indeed, comes away at that time, as the after-birth, and the 

 separation of this portion takes place by a rending or crush- 

 ing through of that part at which its cohesion is least strong, 

 namely, where it is most burrowed and undermined by the 

 cavernous spaces before referred to. In this way it is cast 

 off with the foetal membranes and the decidua vera and 

 reflexa, together jvith a part of the decidua serotina. 

 The remaining portion withers, and disappears by being 

 gradually either absorbed, or thrown off in the uterine 

 discharges or the lochia, which occur at this period. 



A new mucous membrane is of course gradually de- 

 veloped, as the old one, by its peculiar transformation into 

 what is called the decidua, ceases to perform its original 

 functions. 



The umbilical cord, which in the latter part of foetal life 

 is almost solely composed of the two arteries and the single 

 vein which respectively convey foetal blood to and from the 





