THE SOURCE OF THE AMNIOTIC AND ALLANTOIC FLUIDS IN MAMMALS. 83 



development there is a current from the maternal blood-serum to the amnion, and in the 

 later stages a current in the reverse direction from amnion to maternal blood-serum. 



Grunbaum (Verhand. de physic, med. Gesellsch. zu Wilrzburg, Bd. xxvii., No. 3, 

 p. 161, 1905; abstract Malys Jahresbericht for 1905) found that the amniotic fluid 

 had a lower molecular concentration than the maternal blood. The freezing-point 

 reduction of the blood is - 53, of the foetal fluids 0'485, and of the foetal urine 0'2. 



In the cow, the molecular concentration of the amniotic fluid is nearly that of the 

 blood till the end of pregnancy, when it becomes less. In the allantoic, the molecular 

 concentration is at first very little different from that of the blood, later distinctly less, 

 and towards the end of pregnancy again becoming nearly the same as the blood. So 

 far as they were investigated, the dog, cat, and goat gave the same results as the cow. 

 In the pig, the amniotic fluid shows a lower concentration than the blood in the second 

 half of pregnancy, and the allantoic a lesser concentration. From these observations he 

 concludes that in man the amniotic fluid is a mixture of transudation and fcetal urine, 

 and that in the cow the amniotic fluid is entirely a transudation, the allantoic fluid in 

 the beginning a transudation and later chiefly fcetal urine. 



The author appears to conclude that, when molecular concentration of one of the 

 fcetal fluids approaches that of the blood, the fluid is to be regarded as a transudation, 

 while if the molecular concentration is lower an admixture with urine is indicated. 



Considering the enormous variations in the relationship between the molecular 

 concentration of the urine and blood in the adult, such a conclusion appears hardly 

 warranted. While normally the A of the blood is 0"56° C, and that of the urine 2'3, the 

 A of the urine may in the caffeine diuresis or after drinking large quantities of beer 

 fall as low as '160. 



Again, the study of the absorption of fluids from serous spaces has shown that the 

 molecular concentration of an effusion may be raised by the absorption from it of water. 

 Thus, alterations in the molecular concentration of the fcetal fluids may be capable of 

 explanation in terms of the relative activity of formation on the one hand and absorp- 

 tion on the other. 



The conclusions arrived at by the study of the molecular concentration of the fluids 

 have thus a somewhat unsatisfactory basis. 



It appeared to us that more light might be thrown upon the question of the relative 

 part played by transudation on the one hand, and secretion by the kidneys on the 

 other, by a more careful analysis of the results of our experiments on the injection of 

 substances into the maternal blood, and a study of the chemistry of the fluids. 



(2) Evidence from the injection of Substances into the Maternal Blood. — The 

 most convincing experiment is No. IX., on a bitch. Here fluorescin, sodium salicylate, 

 and sodium iodide were injected. The combined urines of the foetuses were very 

 strongly fluorescent, but the fluids of only one pregnancy sac showed a slight 

 fluorescence. The fcetal urines gave strongly the reaction for salicylic acid, but the 



