EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 55 



terms chorion) was deeply stained but the amnion was not. He shows an illustra- 

 tion in which the endothelial cells of the inverted yolk-sac are seen heavily laden 

 with dye, while the amniotic epithelium contains none. 



The only complete observations on the behavior of the fetus toward injected 

 foreign colloids are those of Goldmann (1909), who studied the mouse and rat 

 with great care. Into a number of pregnantm ice and rats he injected colloidal 

 solutions of the benzidine dyes, pyrrhol-blue and trypan-blue. These dyes are 

 practically non-toxic to living tissue. The result was that in every instance the 

 tissues of the mother became deeply stained, the dye appearing in the form of blue 

 granules in many of the cells of the body. On opening the uterus of such a vitally 

 stained animal the fetuses were found unstained, the dye apparently having been 

 prevented from entering their bodies by the placenta and membranes, all of which 

 were a dark blue. On examining sections of the placenta and membranes, Goldmann 

 found that the dye had been absorbed by many of the fetal cells and appeared in the 

 form of blue granules within their cytoplasm; to tins circumstance he attributed 

 the failure of the dye to reach the fetal circulation. In the placenta he observed 

 the dye in the fetal ectoderm, particularly in the giant cells or angioblasts, and in 

 the entire chorionic epithelium of the labyrinth which separates the maternal blood- 

 spaces from the fetal capillaries. The decidual cells, as well as the mesenchyme 

 of the villi and the endothelium of the fetal capillaries, were unstained. He saw 

 further that the dye was very abundant in the endodcrmal cells of the inverted yolk- 

 sac. In Ins earlier paper Goldmann claimed that the amnioticfluid was stained blue 

 and he believed that it consequently must be a secretion from the neighboring vitally 

 stained endothelium of the yolk-sac and hence derived ultimately from the maternal 

 blood-stream. In a later publication (1913) he contradicts his former assertion 

 regarding the staining of the amniotic fluid. 



Concerning the significance of vital staining in the placenta, several opinions 

 have been advanced. Schlecht (1907) believes that the chief function of the 

 vitally stained chorionic cells is to protect the fetus from toxic substances in the 

 maternal blood-stream. Goldmann sees in them a group of cells which are tre- 

 mendously important in the storage of nutrient material for the fetus. He was 

 led to this view by demonstrating that these same cells are normally laden with 

 glycogen and give staining reactions for iron and fat. 



Goldmann's work upon the placenta was confined to rats and mice, whose 

 embryology is nearly alike, and he found that these two genera behaved the same 

 toward vital dyes. In view of the dissimilarity in the development of the placenta 

 and fetal membranes in the different orders of mammalia, it is surprising that no 

 further studies on the action of vital dyes in pregnant animals have been under- 

 taken. 



Turning to the laboratory animals — the mouse, rat, guinea-pig, rabbit, cat, 

 dog, and monkey — one finds that they all belong to the Deciduata, but that they 

 fall into three orders: Rodentia, Carnivora, and Primates. In the development of 

 the placenta and fetal membranes these orders exhibit distinct and characteristic 

 differences which it will be of interest to consider in the light of vital staining. 

 The present study concerns the behavior of the placenta and fetal membranes of 



