Many tricks can be used to facilitate grafting and explanting embryonic tissues. Although these tricks provide advantages in some situations, they usually come with liabilities. High pH and or low calcium makes tissues easier to separate or cut, but also retards healing. Hypertonicity and hypotonicity may facilitate separation of layers of cells, by shrinking or swelling the cells, but may retard healing, and kill or damage cells. In cutting through the epithelial surface of the embryo, either the epithelial or the deep cell populations will be at a disadvantage, depending on what solution is used. The deep cells and basolateral surfaces of the epithelial cells require high salt, whereas the outer surface of the epithelium is normally exposed to low salt. External solutions of high pH and/or high salt cause lesions in the epithelial layer and increased cell motility at these lesions, particularly in the case of high pH. Conversely, low pH and low salt cause sluggish or abnormal motility or swelling of deep cells, respectively. These facts, discovered by Holtfreter (see refs. 71-73), make any grafting or explantation operation suboptimal for the health and function of one cell population or the other.
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