In the earlier months of pregnancy the amniotic fluid is not abundant; later it increases rapidly, so that by the end of the period it measures about a quart, and frequently even more. The slightly yellow amniotic fluid is itself clear, but small particles of dead skin and other material cast off from the surface of the child's body are floating in it, and may cause turbidity. The absence of odor supports the view that this fluid is not the child's urine. The evidence thus far adduced, though not absolutely conclusive, gives good reason to believe that "the waters" are secreted by the inner side of the sac which incloses the fetus. Very early in pregnancy this sac becomes a double-walled structure; and, though its layers are intimately blended, and together measure not more than 1/16 of an inch in thickness, with a little care they can be separated. The outer layer, which comes in contact with the inner surface of the uterus and has to do with the matter of nutrition, is called the Chorionic Membrane; the inner, the so-called Amniotic Membrane, is much the stronger and is devoted to the protection of the embryo, which it completely surrounds with fluid, at the same time retaining the fluid within set bounds. The amniotic fluid performs many important duties. Perhaps the first, in point of time, is to provide sufficient room for the embryo to grow in. Later, as the fluid increases, it permits the fetus to move freely, and yet renders the movements less noticeable to the mother. Again, the amniotic fluid prevents injuries that might otherwise befall the child in case the mother wears her clothing too tight. Harmful as the practice of tight-lacing during pregnancy is, it does not, thanks to the presence of the amniotic fluid, result in the disfigurement of the child. For the same reason a blow struck upon the abdomen, as in a fall forward, is not so serious as might be thought, since the fluid, not the child, receives the force of the impact. Some physicians believe that the fetus swallows the amniotic fluid and thus secures nourishment. The fluid also serves to keep the fetus warm; or, to be more exact, protects it from sudden changes in the temperature of the mother's environment. Normally the temperature of the fetus is thus kept nearly one degree higher than the temperature of the parent.