98 D. NOEL PATON, B. P. WATSON, AND J. KERR ON 



3rd. The existence of a peculiar sugar — laevulose — in the fluids, and also in the 

 foetal urine. 



4th. Proteins, which are generally, although not always, present in the fluids, have 

 been found in the fcetal urine. 



5th. Gusserow observed that, when benzoic acid is injected into the mother, hip- 

 puric acid appears in the fcetal fluids. 



6th. Such substances as sodium iodide, sodium salicylate, and fluorescin, which, 

 when injected into the maternal circulation, appear in the fcetal fluids, are found in much 

 greater abundance in the fcetal urine and tissues. 



All investigators who have recognised the foetal origin of the fluids admit that the 

 allantoic fluid is at least mainly urinary in nature, but it has been maintained by most 

 that the amniotic fluid is a transudation. 



Thus Ellenberger ( Vergleichende Physiologie der Haussaugthiere, Bd. ii. p. 523, 

 1892) says : " The amniotic fluid is a transudation from the rich cutaneous vessels of the 

 embryo ; later it is also possibly derived from the vessels of the allantois which surround 

 the amnion, . . . into which, towards the end of pregnancy, urine and saliva may escape." 



Doderlein also regards the amniotic fluid as a transudation, basing his conclusion 

 entirely upon the correspondence between the salts of the fluid and those of the blood- 

 plasma, and ignoring his own results upon the non-protein nitrogen and the other 

 evidence which is forthcoming. 



The last question which must be discussed is a very difficult one. Admitting the 

 origin of both fluids as essentially a secretion from the fcetal kidneys, does any exchange 

 go on between the fluids, separated as they are by only a thin double membrane '? 



The facts to be taken into consideration in dealing with this question seem to be 

 the following. They are diagrammatically represented in fig. 2 : — 



1st. The relatively rapid increase of the amniotic fluid as compared with the allantoic. 



2nd. The steady increase of the sp. gr. of the allantoic fluid without any change 

 in the sp. gr. of the amniotic, and the fact that in the early stages the sp. gr. of the 

 two fluids is the same. 



3rd. The steady increase of non-protein nitrogen in the allantoic fluid, and the 

 slighter increase of the nitrogen of the amniotic fluid. 



4th. The high proportion of urea nitrogen in the amniotic fluid and the steady 

 decrease in the proportion of urea nitrogen in the allantoic fluid. 



5th. The steady increase of sugar in the amniotic fluid, so that at the end of 

 pregnancy it becomes equal to, or greater than, the percentage in the allantoic, which 

 from the beginning remains fairly steady. 



6th. The high chlorine content of the amniotic fluid as compared with the 

 allantoic throughout pregnancy, and the low magnesium content of the same fluid. 



The higher chlorine and possibly the higher sodium content (Doderlein, Kerr), with 



