The effects of the release of normal distractive forces from the rabbit's tendo-achilles by distal tenotomy and proximal sciatic neurectomy alone, and in combination, have been studied. The results demonstrate that:

1. Complete release of distractive forces from the tendon is followed by changes in collagenous architecture and an increase in cell size and cell population, particularly at the musculotendinous junction.

2. The changes in the resident cell population and the cells migrating into the tendon from the musculo-tendinous junction and perivascular spaces are associated with the production of increased quantities of mucopolysaccharide and the disaggregation of collagen fibres in the vicinity.

3. In the initial stages this increased mucopolysaccharide appears to be predominantly unsulphated material – probably hyaluronic acid, but with the reapplication of tension which follows spontaneous repair of the divided tendon, this is replaced by a sulphated polymer which appears to be associated with the reaggregation of collagen fibres at this stage.

4. The implications of this biphasic production of mucopolysaccharide, and its effect on the stability and integration of collagen, are discussed.

5. During this study it was found that the Masson's trichrome stain appears to be a precise indicator of the state of tension of collagen fibres within the tendon, and other connective tissues.

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