926 CARE AND NOURISHMENT OF THE DEVELOPING YOUNG 



or the puppy will suffocate. In the human the after-birth consists of the 

 following: 



(a) the maternal membranes — decidua vera, decidua basalis, and decidua 

 capsularis (vera), and 



(b) the fetal membranes — chorion frondosum, chorion laeve, amnion, yolk 

 sac, allantois, and umbilical cord. 



D. Functions of the Placenta 



The functions of the placenta are many, and the more intimate the contact 

 with the maternal tissue the functions appear to increase. The various func- 

 tions of the placenta may be listed as follows: 



( 1 ) Food materials pass from the maternal blood stream to the blood 

 stream of the embryo. 



(2) Waste materials pass from the embryo's circulatory system to the 

 blood stream of the mother. 



(3) Serves as the external respiratory mechanism for the embryo. 



(4) It functions to elaborate two ovarian hormones, estrogen and proges- 

 terone (see Chapter 2) together with chorionic follicle-stimulating and 

 luteinizing hormones. The production of estrogen and progesterone 

 helps maintain pregnancy (see Chapter 2) and at the same time 

 brings about the development of the mammary glands. 



(5) The placenta and after-birth tissues form a source of nourishment to 

 the female of many mammals, for it is generally eaten by the mother. 



E. Tests for Pregnancy 



The elaboration of chorionic follicle-stimulating and luteinizing hormones 

 by the placenta in increasing amounts during the first part of pregnancy and 

 their excretion by the kidneys makes possible certain tests for the detection 

 of pregnancy (see Engle, '39). 



1. ASCHHEIM-ZONDEK TeST 



Aschheim and Zondek were the first investigators to detect gonad-stimu- 

 lating principles in the urine of pregnant women. The excretion of these sub- 

 stances in pregnancy urine begins during the second week, about the fifteenth 

 day, rises sharply to the thirtieth day and then gradually falls to the ninetieth 

 day (Siegler and Fein, '39). This secretion probably is elaborated by the 

 trophoblast of the developing chorion during the second week of pregnancy 

 and later by the epithelium of the chorionic portion of the placenta. The pres- 

 ence of these gonad-stimulating substances in the urine provokes reproductive 

 changes in the ovaries of common laboratory animals when injected with the 

 urine. Aschheim and Zondek were the first to use this method for detecting 

 pregnancy. The method consists of the injection of small amounts of preg- 



