THE NATURAL HISTORY OF MAN 59 



blood in the placental sinuses in the early stages of develop- 

 ment. Many nucleated red corpuscles which are found only 

 in the blood of the fetus will be seen in the vessels of the 

 placental villi but there are none in the placental sinuses. 

 Further, the vessels in the placental villi can be injected from 

 the fetal but not from the maternal blood vessels. 



That gases can be transmitted from the maternal to the 

 fetal circulation is shown by the fact that the blood in the um- 

 bilical vein, which carries blood from the placenta to the fetus, 

 is redder and contains more oxygen than the darker blood of 

 the umbilical artery, which carries blood from the child to the 

 placenta. Also ether or chloroform administered to the 

 mother can be demonstrated in the blood of the child. 



Substances in solution also can pass from the maternal to 

 the fetal blood. This is indicated by the fact that the child 

 grows. Also it has been experimentally demonstrated in the 

 case of many drugs that when they are administered to the 

 mother they will be found in the blood of the child. Among 

 these drugs are bromide of potassium, arsenic, strychnine, 

 quinine, and morphine. 



The work of recent observers seems to show that fats and 

 proteins are not passed unchanged through the walls of the 

 placental villi from maternal to fetal blood, but are broken 

 down into simpler compounds and later recombined, thus mak- 

 ing the process of absorption in the placenta somewhat analo- 

 gous to that occurring in the intestine. The placental tissue 

 apparently has not only the power to change some substances 

 but also the power of specific absorption. Proteolytic, lipo- 

 lytic, and glycolytic ferments have been demonstrated in the 

 placental villi, also a ferment which changes certain of the 

 amino acids into ammonia. 



Observers now generally agree that, while the placenta 

 usually acts as an efficient filter against bacteria, occasionally 

 bacteria may be transmitted from mother to child as has been 



