THE SOURCE OF THE AMNIOTIC AND ALLANTOIC FLUIDS IN MAMMALS. 97 



{Daten und Tabellen, p. 333) gives a table based upon analyses of Schmidt and 

 Vogel showing a content of NaCl in the blood- plasma of "5 5 46 per cent., and in the 

 urine of 1'10 per cent., while in flesh and many other constituents of the body the 

 proportion of magnesium is greater than that of calcium. It seems unsatisfactory to 

 attempt to draw conclusions as to the source of the fluids from their inorganic 

 constituents. 



III. Summary of Evidence and Conclusions. 



To sum up the evidence at our disposal : — 



1. As against the fluids being of maternal origin, it has been shown : — 

 1 st. That anatomically this is improbable. 



2nd. That pathological evidence gives no support to the idea. 



3rd. That, after the foetus has been killed by withdrawing the fluid, no re-formation 

 of the amniotic fluid occurs, although the maternal uterus and placenta remain normal. 



4th. That various substances injected into the maternal vessels appear in the 

 fluids only after first being in the foetus. 



The only evidence in favour of the maternal origin of the fluids is the experimental 

 work of Zuntz and Wiener with sulphindigotate of soda on rabbits — the probable 

 fallacies of which have been explained. 



2. As against either of the fluids being formed as a transudation from the foetal 

 blood-vessels in the wall of the allantois may be adduced : — 



1st. The absence of the proteins of the blood-plasma from the amniotic fluid of the 

 sheep and from the allantoic fluid of the dog. Their presence in the fluids of other 

 animals cannot be considered as indicating their origin as transudations, since these 

 proteins are present in foetal urine. 



2nd. The observations recorded on the molecular concentration of the fluids and 

 on the changes which this undergoes throughout pregnancy afford no evidence of 

 their formation as transudations. 



The only evidence of an exchange between these vessels and the fluids is the fact 

 that sodium iodide is so readily absorbed from the fluids and passed through the 

 placenta into the maternal circulation. But the absorption of such a substance into 

 the blood-vessels does not prove that normally fluid passes from these vessels into 

 the foetal fluids, any more than its absorption from the bladder proves that normally 

 the urine is secreted from the bladder wall. 



3. That the fluids are of the nature of urine derived by secretion from the foetal 

 kidney is indicated by the following facts : — 



1st. The anatomical connection of the two cavities with the foetal urinary system. 

 2nd. Both fluids contain a considerable proportion of nitrogen in urea and allied 

 compounds. 



