[Insensitivity of some rats to intraperitoneal injections of collagenase and trypsin]

In the rat peritoneal injections of collagenase or trypsin give rise to severe lesions. In our experience 20% of the animals remain intact. The frequency of lesions increases with older and heavier subjects. Moreover 25% of the rats who remained free of lesions after a first injection of collagenase resist to a second one. This shows that they are strongly protected against the enzyme. The exact nature and location of this protective mechanism are not known.