Abstract
A comparative study has been made of the susceptibility to trypsin and to collagenase of collagen and some proteins thought to be related to it. These include a crude reticulin made from embryonic calf renal midcortex and soluble collagens initially extracted from skins at alkaline or acid reactions. With minor variations all these materials are readily hydrolysed by collagenase and are rather resistant to trypsin. In all cases of hydrolysis by collagenase the solubilized portion contains hydroxyproline only in peptide form.