100 EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 



Beneath the layer of giant cells lies the outermost or decidual layer of the 

 placenta, composed of decidual cells, many of which were found to be undergoing 

 degeneration. This layer is traversed by conspicuous maternal vessels which pass 

 to and from the labyrinth. Try pan blue was present only in the cells which were 

 degenerating and whose cytoplasm and nuclei, as a result, stained diffusely. The 

 uterine musculature was noteworthy because of the number of vitally stained 

 macrophages visible in its connective-tissue septa. 



SUMMARY. 



1. Trypan blue injected into the maternal blood-stream of the pregnant rabbit 

 stains the placenta and vitelline membrane. 



2. The dye passes in traces from the maternal into the fetal circulation, staining 

 the fetus and amniotic fluid very slightly. 



3. The dye is stored in the form of granules in the cells of the vitelline membrane 

 and in the syncytium and giant cells of fetal origin in the placenta. 



CONCLUSIONS. 



Our knowledge concerning the behavior of the placenta and fetal membranes 

 toward colloidal dyes injected into the blood-stream may be summed up as follows: 



Finely dispersed colloids, such as trypan blue and pyrrhol blue, when injected 

 intravenously into the pregnant animal, reach the placenta and are there absorbed 

 and stored in the form of granules in the chorionic ectoderm. In the mouse and 

 rat the dye passes in traces into the amniotic fluid but fails to stain the fetus 

 (Goldmann). In the guinea-pig and rabbit it likewise passes in traces to the amni- 

 otic fluid, but in addition it faintly stains the fetus. In the cat vital dyes are not 

 transmitted, even in traces, to the amniotic fluid or to the fetus (Wislocki, 1920). 

 This variation in behavior may be explained on comparative anatomical grounds, 

 differences of architecture making the placenta of carnivora less permeable than 

 that of rodentia. Vital dyes are also absorbed and concentrated into granules in 

 the cytoplasm of the cells of the vitelline membrane, which in rodentia forms the 

 outermost fetal covering. Granules of dye are deposited in a structure peculiar to 

 carnivora, termed in the cat the "brown border," which is a modified portion of the 

 chorionic membrane bordering the placenta. 



