EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 95 



velocity of the blood-stream is diminished, or outside of the blood-vessels, the 

 leucocytes stain with vital dyes, and he believes that this staining is quite compar- 

 able to that seen in macrophages. The question is still debatable whether or not 

 his assumption is correct and whether the staining should be considered as physio- 

 logical rather than as an indication of cell injury. 



The placentse in which the staining of the polymorphonuclear leucocytes was 

 observed showed evidence of slight inflammatory changes, but there was nothing 

 in the appearance of the leucocytes themselves to condemn them as moribund. 

 Further evidence is necessary, however, before it can be decided definitely whether 

 or not true vital staining of polymorphonuclear leucocytes ever occurs. 



In conclusion, a few observations upon the fate of a fine suspension of carbon 

 particles, such as one finds in india ink, injected into the blood-stream of the preg- 

 nant guinea-pig, will be described. Several animals were injected and killed on the 

 second, fourth, and sixth day thereafter, respectively. In these animals the liver 

 and spleen appeared very black while the color of the other abdominal organs was 

 almost normal. On opening the thorax the lungs were seen to contain considerable 

 carbon. The bone-marrow was also conspicuously black, and traces of carbon were 

 visible to the unaided eye in many other tissues, such as the ovaries, pancreas, 

 omentum, diaphragm, and mesentery. In the uterus, placenta, or vitelline 

 membrane, however, no carbon was recognizable. The fetuses appeared perfectly 

 normal, the amniotic fluid clear and colorless. Under the microscope particles 

 of carbon were found in great abundance in the liver, spleen, and lungs, where 

 they had been phagocytosed by endothelial and connective-tissue cells. In the 

 omentum, mesentery, bone-marrow, and diaphragm, similar but less numerous 

 particles were encountered ; in the placenta and fetal membranes, on the other hand, 

 there was not even a trace of carbon. 



In order to determine whether the cells of the vitelline membrane refuse under 

 all circumstances to take up carbon particles, a small quantity of ink was injected 

 directly into the uterine cavity in the region of the villi. Microscopic examination 

 of the villi after this experiment showed that the cells covering them did not take 

 up a single particle of carbon into their cytoplasm, although they were seen actively 

 engaged in the absorption of hemoglobin. It appears, therefore, that the endoder- 

 mal cells of the vitelline membrane and the chorionic epithelium of the placental 

 labyrinth are unable to phagocytize particles as coarse as those of india ink, although 

 they are capable of absorbing a substance as finely dispersed as trypan blue. 



