Development of Acid-Base Control 219 



hoped to extend the study to later stages of gestation, to 

 other membranes and to glutaminase. 



It is an open question at present whether the fluid found in 

 the sac at 45 days is a hypotonic urine elaborated by the foetal 

 kidney and similar to that formed by the human kidney 

 before birth, or whether the fluid has been made hypotonic 

 and acid by the action of the membranes themselves. Small 

 amounts of fluid have been removed from the bladders of 

 foetuses at 45 days and it is probably possible also to with- 

 draw fluid from the large mesonephric duct, so that this 

 problem may be soluble without recourse to large-scale 

 experimental veterinary obstetrics. Should it turn out that 

 the composition of the fluid is being altered by the membranes, 

 their activities may contribute materially to our ideas about 

 the function of the renal tubules. 



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