EXPERIMENTAL STUDIES ON FETAL ABSORPTION. 



By George B. Wislocki. 



I. THE VITALLY STAINED FETUS. 



Colloidal dyes and particulate matter introduced into the blood-stream of 

 pregnant animals fail to reach the fetus. The placenta appears to be an impene- 

 trable barrier for inert colloids, and experiments show that even colloidal metabo- 

 lites reach the fetus only after they have been split into simpler substances by 

 enzyme action, hydrolysis, and other chemical processes. Goldmann (1909, 1912) 

 noticed that when he injected colloidal dyes (particularly trypan-blue and pyrrhol- 

 blue) into pregnant mice and rats the placentae and the fetal membranes stained 

 very deeply with the coloring matter, but none of it reached the fetuses. 



Because colloidal dyes have been of such great value in the study of problems 

 of absorption and phagocytosis in the adult animal it has been a cause for regret 

 that there has existed no simple means of applying these substances to the study of 

 similar processes in the fetus. The writer (1916) first observed that amphibian 

 larvae could be vitally stained by immersing them in dilute solutions of colloidal 

 dyes and his experiments led to further interesting observations by McClure (1918) 

 and Clark ( 1918) . The staining of fetuses appeared more difficult since it had been 

 shown that injecting the dyes into the maternal blood stream was fruitless as a 

 means of staining the embryo. The technical difficulties accompanying direct 

 introduction of the dyes into the fetal circulation are numerous, and in such pro- 

 cedures physiological conditions can not be maintained. It was therefore gratify- 

 ing to observe that by injecting colloidal substances into the amniotic cavity they 

 could be introduced into the fetus with perfect ease and under physiologically 

 normal conditions. The present study concerns the results of injecting colloidal 

 dyes and other substances into the amniotic sacs of guinea-pigs. A few observations 

 of the same sort upon fetal cats are also described. The observations upon cats, 

 although incomplete, are deemed important because they confirm some of those 

 upon the guinea-pig and therefore the final deductions assume a broader significance. 



Sterile operative technique was used in the experiments. The pregnant animal 

 was anesthetized and a mid-line laparotomy was done. One horn of the pregnant 

 uterus was brought into view through the incision. After palpating a fetus through 

 the uterine wall, it was grasped between thumb and index finger of the operator. 

 If the fetus was so young that the amniotic cavity was completey distended with 

 fluid, a replacement injection was performed. The technique of replacement 

 injections is described by Weed (1917). As applied to this study, it consists of 

 inserting two 24-gage needles, connected with balanced reservoirs, directly through 

 the uterine wall into opposite poles of the amniotic cavity and permitting the 

 injection fluid to enter by one needle, while the amniotic fluid escapes through the 

 other. In older fetuses, where the amniotic sac is incompletely distended with fluid, 



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