520 THE HUMAN BODY 



supplying from her blood nutriment for the fetus, but also, 

 through her lungs and kidneys, getting rid of its wastes; the result 

 is a strain on her whole system which, it is true, she is constructed 

 to bear and will carry well if in good health, but which is severely 

 felt is she be feeble or suffering from disease. The healthy married 

 woman who endeavors to evade motherhood because she thinks 

 she will thus preserve her personal appearance, or because she dis- 

 likes the trouble of a family, deserves but little sympathy; she is 

 trying to escape a duty voluntarily undertaken, and owed to her 

 husband, her country, and her race; but she whose strength is un- 

 dermined and whose life is made one long discomfort for the sexual 

 gratification of her husband deserves eveiy consideration, and the 

 family physician ought perhaps to warn the husband more fre- 

 quently than he does of the risk to a delicate wife's health, or even 

 life, of frequent pregnancies : and the husband should control him- 

 self accordingly. 



The Intra-Uterine Nutrition of the Embryo. At first the em- 

 bryo is nourished by absorption of materials from the soft vas- 

 cular lining of the womb; as it increases in size this is not suffi- 

 cient, and a new organ, the placenta, is formed for the purpose. 

 A fetal outgrowth, the allantois, plants itself firmly against the 

 decidua serotina, and villi developed on it burrow from its surface 

 into the uterine mucous membrane. In the deeper layer of this 

 latter are large sinuses through which the maternal blood flows, 

 and into which the allantoic villi project. Blood is brought from 

 the fetus to the allantois by arteries and carried back by veins 

 after traversing the capillaries of the villi, and while flowing 

 through these receives, by dialysis, oxygen and food materials 

 from the maternal blood, and gives up to it carbon dioxid, urea, 

 and other wastes. There is thus no direct intermixture of the two 

 bloods; the embryo is from the first an essentially separate and 

 independent organism. The allantois and decidua serotina be- 

 coming inseparably united together form the placenta, which in 

 the human species is, when fully developed, a round thick mass 

 about the size of a large saucer, connected to the embryo by a 

 narrow stalk, the umbilical cord, in which blood-vessels run to and 

 from the placenta. 



Parturition. At the end of from 275 to 280 days from fertiliza- 

 tion of the ovum (conception) pregnancy terminates, and the child 



