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



not interfere with the diffusion of sugar, and hence the percentage of that substance in 

 the amnion would tend to rise till it equalled that in the allantoic fluid. But if such 

 exchanges go on, it is difficult to explain the persistence of the high chlorine content of 

 the amniotic fluid. Why should it not pass into the allantoic fluid ? Or is it possible 

 that the passage of water and diffusible solids can take place only from allantois to 

 amnion, but not in the reverse direction ? 



The whole question of these exchanges is further complicated by : — 



(a) The continuous addition of urine to the allantoic fluid. 



(b) The intermittent addition of urine to the amniotic fluid. 



(c) The possible absorption of allantoic or even of amniotic fluid by the blood-vessels 

 going to the placenta. 



These various considerations do not affect our main thesis, that both foetal fluids are 

 essentially derived from the foetus through the kidney. 



Our thanks are due to Mr A. M. Trotter, M.R.C.V.S., for his kindness in procuring 

 for us a considerable amount of the material used in these investigations. 



APPENDIX. 



The Method used for Detection and Estimation op Iodide. 



The process employed for the detection and approximate determination of the iodide 

 was as follows : — 



The specimen was ignited to ash after addition of solid sodium carbonate. The ash 

 was boiled with water, filtered, concentrated to definite volume. 



A measured volume of the solution was taken, such that it contained not more than 

 0*0005 gramme of iodide calculated as sodium iodide, 1 c.c. of chloroform added, and 

 1 c.c. of concentrated solution of potassium nitrite, and the mixture acidified with dilute 

 sulphuric acid. 



The colour of the resulting solution of iodine in chloroform was then compared with 

 the colour obtained by the same process from a standard solution of iodide. 



The smallest quantity of iodide which could be detected by this method was 

 equivalent to '00003 6 gramme of sodium iodide. 



A blank experiment was conducted, and gave no indication of iodide. 



Determination of Chloride. 



A measured quantity of fluid was evaporated to dryness in a platinum basin, after 

 addition of some pure solid sodium carbonate. 



The residue was carefully carbonised, digested with dilute nitric acid, and to the 

 solution a measured excess of standard silver nitrate solution was added. 



The precipitated silver chloride was filtered off, and the excess of silver nitrate in 



