No agreement has yet been reached on the opposing theories of Hueter and Volkmann on the one hand and Julius Wolff on the other. The writer's experiments with young dogs were made in order to contribute to the clarification of these controversial theories. The findings permit the following conclusions:

1. A permanent and maximum degree of pressure inhibits longitudinal bone growth and does not lead to a compensatory increase in girth. This inhibition of growth is due to the prevention of proliferation in the growth cartilage, which narrows and becomes irregular in its arrangement. New-bone formation, that is, the replacement of the available cartilaginous tissue, proceeds without any interruption. Atrophy of the bones does not occur.

2. Strong and permanent tension does not increase enchondral bone growth; on the contrary, it has nearly the same effect as compression when it is applied directly to the bone. The nature of the insertion of the ligament at the apophysis seems to be such that there is no danger of extreme unphysiological tension.

3. Changes caused by mechanical forces appear to be reversible to a certain extent, if these forces are removed before skeletal maturation.