EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 



59 



CONCLUSIONS. 



It appears that inert colloids are normally not transmitted through the mam- 

 malian placenta or membranes and consequently can not enter the fetal circulation 

 or the fluids surrounding the embryo. The outermost fetal membrane, whether it 

 be of ectodermal origin as in carnivora, or endodermal as in rodents, invariably fails 

 to transmit such substances. 



The chorionic ectoderm of the placenta possesses, in all the animals investigated, 

 the ability to absorb and store foreign colloids. It is interesting to note that in 

 the fetus vital dyes are absorbed and stored in both ectoderm and endoderm, 

 germ layers which in the adult rarely (choriod plexus) participate in their storage. 

 Cells of all three germ layers may under suitable conditions stain vitally, and it 

 appears that the power to ingest benzidin dyes is not limited to any one class or 

 group of cells. 



The deposition of vital dyes is greatest in those cells of the placenta and fetal 

 membranes in which the metabolic exchange between mother and fetus is most 

 active. It represents an accumulation of unassimilable material along the path- 

 ways between mother and fetus. 



Hofbauer (1905) has pointed out the striking similarity between the placenta 

 and intestines in their power of absorption and excretion. A fundamental differ- 

 ence would seem to exist in their behavior toward trypan-blue. Whereas the dye 

 becomes aggregated in large amount in the chorionic cells, none of it is absorbed by 

 the intestinal mucosa. Why particles the size of trypan-blue should readily enter 

 and be stored in the chorionic but not the intestinal epithelium is a question which 

 requires further study. 



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