(Hodge)] The formative activity of cells is also essential to the normal state.
Destruction of cells is constantly taking place in the body, and more rapidly in certain tissues than in others.

Dried and dead cells are constantly and in great numbers thrown off from the surface of the skin: such epidermic appendages as the hair and nails grow and are removed, millions of cells are represented in the beard which is daily removed.

Cells are constantly being destroyed on the intestinal surface and in the glands.

There is an enormous destruction of the blood cells constantly taking place, certain essential pigments, as that of the bile, being formed from the haemoglobin which the red blood corpuscles contain and which becomes available on their destruction.
All such loss of cells must be made good by the formation of new ones and, as in the case of the nutritive and functional activity, the loss and renewal must balance.

The formative activity of cells is of great importance, for it is by means of this that wounds heal and diseases are recovered from.