1. Add sodium chloride injection to the germ layer medium.

2. Germ layer --- One of three distinct layers of cells that arise in the inner cell mass, the ectoderm, mesoderm, and endoderm, each of which develops into a distinctly different tissue in the embryo.

3. The middle embryonic germ layer, lying between the ectoderm and the endoderm, from which connective tissue, muscle, bone, and the urogenital and circulatory systems develop.

4. Mesoderm --- The middle germ layer in the early embryo; the source of cells that go on to make bones, muscles, connective tissue, heart, hematopoietic system, kidney, and other organs.

5. Methods: Add sodium chloride injection to the germ layer medium.

6. This suggests germ layer boundaries are less absolute than previously thought.