806 GENERATION. 



COMPOSITION OF THE AMXIOTIC FLUID. 



Water 991-00 to 975-00 



Albumen and mucine 0-82 " 10'77 



Urea 2-00 " 3'50 



Creatine and creatinine (Scherer, Robin and Vercleil) not estimated 



Sodium lactate (Vogt, Regnauld). a trace 



Fatty matters (Rees, Mack) 0-13 to 1-25 



Glucose (Bernard) not estimated 



Sodium chloride and potassium chloride 2-40 to 5-95 



Calcium chloride a trace 



Sodium carbonate a trace 



Sodium sulphate a trace 



Potassium sulphate (Rees) a trace 



Calcareous and magnesian phosphates and sulphates 1'14 to 1*72 



The presence of certain of the urinary constituents in the amniotic fluid 

 has led to the view that the urine of the foetus is discharged in greater or less 

 quantity into the amniotic cavity. Bernard, who is cited in the table of com- 

 position of the amniotic fluid as having determined the presence of sugar, 

 has shown that in animals with a multiple placenta, the amnion has a glyco- 

 genic action during the early part of intraiiterine existence. 



With regard to the origin of the amniotic fluid, it is impossible to say 

 how much of it is derived from the general surface of the foetus, how much 

 from the urine, and how much from the amnion itself, by transudation from 

 the vascular structures beneath this membrane. The quantity apparently is 

 too great, especially in the early months, to be derived entirely from the urine 

 of the foetus, and there probably is an exudation from the general surface of 

 the foetus and from the membranes. After the third month the sebaceous 

 secretion from the skin of the foetus prevents the absorption of any of the 

 liquid. An important property of the amniotic fluid is that of resisting pu- 

 trefaction and of preserving dead tissues. 



Formation of the Umbilical Vesicle. As the visceral plates, which will 

 be described hereafter, close over the front of the embryon, that portion of 

 the blastoderm from which the intestinal canal is developed presents a vesicle, 

 which is cut off from the abdominal cavity but which still communicates 

 freely with the intestine. This is the umbilical vesicle. On its surface, is a 

 rich plexus of blood-vessels ; and this is a very important organ in birds and 

 in many of the lower forms of animals. In the human subject and in mam- 

 mals, however, the umbilical vesicle is not so important, as nutrition is 

 secured by means of vascular connections between the chorion and the uterus. 

 The vesicle becomes gradually removed farther and farther from the em- 

 bryon, as development advances, by the elongation of its pedicle, and it is 

 compressed between the amnion and the chorion, as the former membrane 

 becomes distended. 



When the umbilical vesicle is formed, it receives two arteries from the 

 two aortae, and the blood is returned to the embryon, by two veins, which 

 open into the vestibule of the heart. These are called the omphalo-mesen- 

 teric vessels. At about the fortieth day one artery and one vein disappear, 



