AMNIOTIC FLUID. 903 



internal amniotic layer, or the true aniniotic membrane, is closely applied to the surface 

 of the embryon and is continuous with the epidermis at the umbilicus. It is then sepa- 

 rated from the allantois by a layer of gelatinous matter ; and in this layer, between the 

 amnion and the allantois, is embedded the umbilical vesicle. At this time, the umbilical 

 cord is short and not twisted. As development advances, however, the inter-membra- 

 nous gelatinous matter gradually disappears ; the cavity of the amnion is enlarged by the 

 production of a liquid between its internal surface and the embryon ; and, at about the 

 end of the fourth month, the amnion comes in contact with the internal surface of the 

 chorion. At this time, the embryon floats, as it were, in the amniotic cavity, surrounded 

 by the amniotic fluid. The amnion forms a lining membrane for the chorion; by its 

 gradual enlargement it has formed a covering for the umbilical cord ; and, between it and 

 the cord, is the atrophied umbilical vesicle. The amnion then resembles a serous mem- 

 brane, except that it is non-vascular. It is lined by a single layer of pale, delicate cells 

 of pavement-epithelium, which contain a few fine, fatty granulations. At term, the am- 

 nion adheres to the chorion, though it may be separated, with a little care, as a distinct 

 membrane, and may be stripped from the cord. From its arrangement and from the 

 absence of blood-vessels, it is evident that this membrane is simply for the protection of 

 the foetus and is not directly concerned in its nutrition and development. (See Plate 

 III., Fig. 2, facing page 922.) The gelatinous mass referred to above, situated, during 

 the early periods of intra-uterine life, between the amnion and the chorion, presents a 

 semifluid consistence, and it is marked by the presence of numerous very delicate, inter- 

 lacing fibres of young connective tissue and fine grayish granulations scattered through its 

 substance. These fibres gradually develop as the quantity of gelatinous matter diminishes 

 and the amnion approaches the chorion, until, finally, it forms a rather soft, reticulated 

 layer, which is sometimes called the membrana media. 



Amniotic Fluid. The process of enlargement of the amnion shows that the amniotic 

 fluid gradually increases in quantity as the development of the foetus progresses. At 

 term, the entire quantity is variable, being rarely more than two pints or less than one 

 pint. In the early periods of utero-gestation, it is clear, slightly yellowish or greenish, 

 and perfectly liquid. Toward the sixth month, its color is more pronounced, and it be- 

 comes slightly mucilaginous. Its reaction is usually neutral or faintly alkaline, though 

 sometimes it is feebly acid in the latest periods. It sometimes contains a small quantity 

 of albumen, as determined by heat and nitric acid; and there is generally a gelatinous 

 precipitate on the addition of acetic acid. The following table, compiled by Robin, gives 

 its chemical composition : 



Composition of the Amniotic Fluid. 



Water 991*00 to 975-00 



Albumen and mucosine 0'82 " 10'77 



Urea 2'00 " 3'50 



Creatine and creatinine (Scherer. Robin and Verdeil) not estimated 



Lactate of soda (Vogt, Regnauld) a trace 



Fatty matters (Rees, Mack) 0-13 to T25 



Glucose (Cl. Bernard) not estimated 



Chloride of sodium and chloride of potassium 2 - 40 to 5'95 



Chloride of calcium a trace 



Carbonate of soda a trace 



Sulphate of soda a trace 



Sulphate of potassa (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 am- 



