FURTHER EXPERIMENTAL STUDIES ON FETAL ABSORPTION, 



III. THE BEHAVIOR OF THE FETAL MEMBRANES AND PLACENTA OF THE GUINEA-PIG 

 TOWARD TRYPAN BLUE INJECTED INTO THE MATERNAL BLOOD-STREAM. 



Our knowledge of the behavior of vital dyes in the pregnant animal rests upon 

 the careful observations of Goldman (1909) upon mice and rats. He observed that 

 when vital dyes, such as trypan blue and pyrrhol blue, were injected into the 

 maternal circulation, they were not transmitted through the placenta to the fetus. 

 The barriers which prevent the dye from entering the fetus are the chorionic ecto- 

 derm of the placenta and the epithelium of the vitelline membrane. In the rat and 

 mouse the latter constitutes the outermost fetal covering. He also noted the 

 interesting fact that the placenta acts as an attraction center for vital dyes, since, 

 with the initiation of pregnancy in an animal which has been vitally stained, the 

 dye is to a great extent given up by the liver, spleen, and other tissues in which it is 

 stored and is conveyed by the blood-stream to the developing placenta, where it is 

 immediately absorbed by the chorionic epithelium and the endodermal cells of the 

 vitelline membrane. 



The present studies, which are a continuation of a series of investigations on 

 fetal absorption (Wislocki, 1920), concern the behavior of the placenta and fetal 

 membranes of the guinea-pig and rabbit toward trypan blue. Although similar in 

 many respects to the observations of Goldmann on the rat and mouse, there are 

 differences sufficiently great to give interest to a description of the process of vital 

 staining in these rodents. 



The guinea-pigs used in these experiments were stained by the technique 

 usually employed in administering vital dyes. There was no opportunity to study 

 the placenta and fetal membranes in the early stages of their development, and the 

 following description applies only to the period from the time the fetus reaches a 

 length of about 15 mm. up to term. 



In an animal killed at the end of a week after six injections of dye-stuff the 

 maternal tissues were found to be deeply stained. Each fetus was completely 

 surrounded by its vitelline membrane, which was stained dark blue, the color being 

 deepest in a villous zone adjacent to the placenta and fading somewhat towards 

 the antimesometral pole. The amniotic fluid was usually colorless but sometimes 

 showed a slight tinge in deeply stained animals. The amnion, when stripped away 

 from the vitelline membrane and examined in salt solution, as a rule was seen to be 

 uncolored; in rare instances, however, it showed a blue tint, attributable to large 

 and repeated injections of the dye. The fetus and umbilical cord likewise were 

 usually entirely unstained, although a barely perceptible blue coloration of the fetus 

 was noted in several instances, associated with a bluish tinge in the amniotic fluid 

 and membrane. 



Goldmann noticed in the mouse and rat the staining of the amniotic membrane 

 and fluid, but never any of the fetus. He believed that the dye in the amnion must 



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