EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 97 



IV. BEHAVIOR OF THE PLACENTA AND FETAL MEMBRANES OF THE RABBIT TOWARD 

 TRYPAN BLUE INJECTED INTO THE MATERNAL BLOOD-STREAM. 



Successive doses of trypan blue were administered intravenously to six pregnant 

 rabbits, after which the animals were killed. Gestation was more than half 

 completed at the time the last injection was done, and therefore no observations 

 were made during the early stages of development. 



On opening the abdomen the usual distribution of color was observed. The 

 conspicuous uterus, which ordinarily contained from 6 to 12 fetuses, was deeply 

 stained, both on surface view and on section. The placentae were all dark blue. 

 The vitelline, or outermost fetal membrane, was dark blue, the color being deepest 

 in an equatorial zone between the mesometral and antimesometral poles of the 

 fetal sac. The stain faded gradually toward the antimesometral pole, while in the 

 opposite direction it ceased abruptly in the region of the terminal sinus. A band 

 of unstained membrane the chorion Iseve consequently remained between the 

 terminal sinus and the border of the placenta. 



The vitelline membrane, loosely attached to the amniotic membrane by strands 

 of mesoderm, was easily stripped, revealing the delicate amnion inclosing the amni- 

 otic fluid. The amnion itself was faintly stained and the amniotic fluid contained 

 traces of the dye. 



When large and repeated doses of trypan blue are injected into the maternal 

 blood-stream, the amniotic fluid may become quite deeply stained. In such cases 

 the fetus also shows a light staining. In the less deeply stained animals, in which 

 the amniotic fluid contains only a trace of dye, a hardly appreciable staining of the 

 fetus may be observed. Such a staining as this might easily escape detection. It 

 is the writer's belief that the fetus probably contains at all times as much trypan blue 

 as the ajnniotic fluid, but that the dye, when present only in traces, is less readily 

 visible in the fetal tissues than in the amniotic fluid. The escape of traces of dye 

 from the maternal into the embryonic circulation and the amniotic fluid appears to 

 impair in no way the vitality of the fetus. 



The observation that soluble dye-stuffs of various kinds, injected into the 

 maternal blood-stream, can be detected frequently in traces in the amniotic fluid 

 but less often in the fetal tissues, has led a number of investigators to conclude that 

 fluid diffuses directly from the maternal blood-stream into the amniotic fluid, and 

 that it is not necessary for the substances to enter first the fetal circulation; nor are 

 they supposed to reach the amniotic fluid through the placenta, but are thought to 

 enter it directly through the fetal membranes. One theory uses these observations 

 to prove that the amniotic fluid is in whole or in part a transudate from the maternal 

 vessels. 



Leaving the human being out of consideration, the question of the possibility 

 in animals (from observations on which the claim is based) of the formation of the 

 amniotic fluid in this way meets with several grave objections. None of the 

 observers working on rodents have taken into consideration the fact that the 

 amniotic sac is completely surrounded by the vitelline membrane. This membrane 

 possesses an unbroken epithelial surface whose cells are concerned chiefly in the 



