48 EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 



direct injections were made by means of a syringe. For purposes of vital staining 

 1 to 5 c. c. (depending on the age of the fetus) of a 1 per cent trypan-blue solution 

 was injected. After completing the injection the uterus was replaced in the 

 abdomen and the incision closed. Recovery of the animals was uneventful. 



OBSERVATIONS UPON FETAL GUINEA-PIGS. 



The guinea-pig fetuses used in these experiments ranged from 30 mm. to full- 

 term. The technique was found impracticable for younger stages. The pregnant 

 animals, injected as described above, were sacrificed at intervals varying from a 

 few minutes up to several days, and the tissues fixed in 10 per cent formalin. 



Diffusion of trypan-blue from the amniotic cavity of the guinea-pig becomes 

 apparent a few minutes after injection. The fetal membranes turn a uniform dark 

 blue (fig. 1) and within an hour the dye can be demonstrated in the fetal blood- 

 scrum by the filter-paper test. The fetus itself assumes a slaty-blue color which grad- 

 ually deepens (fig. 2) and the placenta becomes a brilliant blue (fig. 1). The stain 

 ceases at a definite line of demarcation between the placental labyrinth and decidua 

 serotina. The uterine wall everywhere about the fetus remains unstained. 



Trypan-blue can not be detected in the maternal circulation, liver, kidneys, or 

 urine, where one would expect to find it in case it escaped, even in traces, from fetus 

 to mother. In a series of nearly full-term fetuses much larger quantities of trypan- 

 blue were injected into the amniotic cavities in order to determine whether the pres- 

 ence of a sufficiently large quantity of dye would cause it to appear in the maternal 

 circulation. In no instance, however, could the dye be detected in the mother. 

 In one animal 30 c. c. of trypan-blue was injected into the amniotic sacs without 

 any of it finding its way into the maternal tissues. It seems reasonable to believe, 

 therefore, that inert colloidal substances can not pass from fetus to mother. From 

 this description it is evident that trypan-blue is rapidly absorbed from the amniotic 

 cavity, enters the fetal circulation, and vitally stains the fetus and placenta. 



Clinicians and veterinarians state that in many animals, and perhaps in man, 

 during the latter part of pregnancy the amniotic fluid normally diminishes. Author- 

 ities for this belief are: Kehrer (1867), who made his observations on rabbits; 

 Doderlein (1890), on the calf; Preyer (1895), on the avian egg; Frank (1901), on 

 ruminants; and Jacque (1903-4), on sheep. Since the amniotic fluid is believed to 

 be partially absorbed during the latter half of pregnancy, curiosity is aroused as 

 to the pathway of absorption. The observations of Zweifel (1875), Ahlfeld (1885), 

 Zuntz (1885), Doderlein (1890), Preyer (1895), and others, who found lanugo hairs, 

 amniotic epithelial cells, and bits of hoof and nail in the stomach and intestines of 

 older fetuses, show clearly that the amniotic fluid may be swallowed by the fetus. 

 These observations appeared to afford such a complete explanation of the partial 

 disappearance of the amniotic fluid that little consideration was given to other 

 possible paths of absorption. One can readily conceive of a number of possible 

 modes of absorption of fluid from the amniotic sac: (1) passage into the gastro- 

 intestinal tract by movements of deglutition ; (2) passage into the respiratory tract 

 by movements of inspiration; (3) absorption through the epidermis of the fetus; 



