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



action of the cells of the ovum. With this earliest production of the fluid we are 

 not concerned. 



In the sheep, the earliest pregnancies examined by us contained embryos of about 

 1"5 grm. in weight, and in these the kidneys and the allantoic blood-vessels are both 

 well developed and the urethra differentiated, while there is something less than 10 c.c. 

 of amniotic and about 50 c.c. of allantoic fluid. 



Before the end of pregnancy these fluids had increased, the amniotic to an average 

 of about 560 c.c, and the allantoic to 90 or 100 c.c. 



In the rabbit, the allantoic circulation and the development of the kidney are 

 completed at about the ninth day. 



From an early stage of pregnancy both the factors under consideration are therefore 

 capable of playing a part in the formation of these fluids, and the evidence as to the 

 part played by each may now be examined. 



(1) The Evidence afforded by the Study of the Molecular Concentration of the 

 Amniotic and Allantoic Fluids and of the Maternal and Fatal Blood. — A good many 

 observations have been carried out along these lines by means of the cryoscope, in the hope 

 of determining whether the fluids are secretions or transudates. The most satisfactory 

 are those by Jacque and those by GtRUNBAUM. 



Jacque (Bull, de VAcad. de Belgique, 1902, p. 218) has examined the allantoic and 

 amniotic fluids of the sheep cryoscopically in order to determine their molecular 

 concentration. This he found always inferior to that of the blood, either foetal or 

 maternal — allantoic fluid, A 0'522 ; amniotic fluid, A 0*538 ; maternal blood, A 0*578 ; 

 foetal blood, A 0'623. From this he concludes that the origin of the fluids is not by 

 transudation but by renal secretion. Further, by observations carried out at different 

 periods of gestation, he finds that the molecular concentration of the two fluids varies. 

 Thus, during the first stages of development, when the allantoic sac communicates freely 

 with the bladder of the foetus, the concentration of the allantoic fluid is lower than 

 that of the foetal urine, and lower than that of the amniotic fluid. At a later period, 

 when the urachus is still patent and the urethra communicates with the amniotic cavity, 

 the liquor amnii and the liquor allantoidis are of the same concentration ; while in the 

 later stages of development, when the urachus is closed but the urethra still com- 

 municates with the amniotic cavity, the amniotic fluid has a higher molecular con- 

 centration than the allantoic. From this he concludes that in the early stages 

 the allantoic fluid is derived from the foetal kidneys through the urachus, and that 

 the amniotic fluid is derived from it by the abstraction of water. In the later 

 stages the amniotic fluid is derived directly from the foetal kidneys by the urethra, 

 and the allantoic is derived from the amniotic by a passage of water back through 

 the membranes. 



Less satisfactory cryoscopic investigations have been carried out by Keim (Bullet, 

 de la Societe d' Obstetrique, 1901), and by Billard, Dieulafe, and Gilles (Comp. 

 Rend, de la Soc. de Biolog., 1905), and they conclude that in the early stages of 



