EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 53 



The maternal tissues remain unstained after injection of trypan-blue into the 

 fetuses. The reverse happens if the dye is injected into the maternal circulation. 

 The tissues of the mother become deeply stained, while those of the fetuses do not, 

 and such a mother gives birth to unstained offspring. The placentae prevent the dye 

 from passing into the fetal circulation, as can be easily demonstrated by examining 

 microscopically a section from the placental labyrinth. The fetal cells separating 

 the maternal blood-spaces from the fetal capillaries contained enormous numbers of 

 fine blue granules within their cytoplasm. The chorion, amnion, yolk-sac, and 

 allantois of the fetus failed to stain, either macroscopically or microscopically, 

 after injection of trypan-blue into the maternal circulation. In several experiments 

 the dye was injected into the space between uterine wall and chorion, but even then 

 it was not absorbed by the fetal membranes. (A detailed account of these obser- 

 vations is given on pages 54-59.) 



Colloidal dyes were absorbed from the amniotic cavity of the cat fetus as readily 

 as from that of the guinea-pig. Trypan-blue was found in the stomach and small 

 intestine of nearly all the fetuses examined. It passed with equal readiness into the 

 trachea and bronchi. The amnion, soon after injection, became intensely stained 

 and gradually the umbilical cord, placenta, and fetus turned blue. The meso- 

 thelium between amnion and allantois is vascularized by numerous branches from 

 the umbilical vessels, and it was through these that absorption occurred. 



It was further observed that when trypan-blue was injected into the allantoic 

 sac of the fetus the allantoic membrane did not stain, nor did absorption of any of 

 the injected dye occur. The allantoic membrane appeared to be impermeable to 

 the dye. It is interesting to recall that the allantoic arises as an outgrowth from 

 the hind-gut and also is thought to be a reservoir for fetal urine. It may also be 

 recalled that in the adult trypan-blue is not absorbed from the urinary bladder. 



CONCLUSIONS. 



1. Substances injected into the amniotic cavity of the guinea-pig and cat are 

 absorbed during the latter half of pregnancy. Absorption occurs in three ways: 

 (a) through the gastro-intestinal tract; (b) through the respiratory tract; and (c) 

 by diffusion through the amniotic membrane. 



2. Amniotic fluid is normally swallowed and also inspired by the fetus during 

 the latter half of pregnancy. 



3. The fetal guinea-pig may be vitally stained by injecting a colloidal dye into 

 the amniotic sac. Vitally stained cells are abundant in the fetus and membranes. 

 The chief of these are the endothelial cells lining the hepatic sinuses, the epithelium 

 of the renal convoluted tubules, the amniotic epithelium, and the endothelial cells 

 of the placental capillaries. The endodermal cells of the yolk-sac are extremely 

 phagocytic toward vital dyes. 



4. Foreign colloidal material can not pass from the fetal into the maternal 

 circulation. 



My appreciation is due Dr. W. C. Quinby for suggestions which were of value 

 in carrying out these experiments. 



