1. Forty-seven tibial nerves of rabbits were stretched, twenty-four gradually by the Instron machine and twenty-three suddenly by dropping a load. The stretched nerves were examined histologically throughout their length.

2. Nerve trunks possess a high degree of elasticity, which is mainly a feature of the epineurium.

3. The initial elongation of the nerve is due to extension of the epineurium and straightening of the funiculi and of the nerve fibres. Such elongation is "physiological" in the sense that it does not affect the nerve fibres.

4. The first structure to be ruptured during stretching is the epineurium ; this occurs when the nerve trunk has reached its limit of elasticity.

5. Before rupture of the epineurium the damage to the nerve fibres is either neurapraxia or axonotmesis, because the endoneurial sheaths and Schwann tubes remain intact.

6. Beyond the limit of elasticity very severe damage of the nerve trunk occurs; all elements of the nerve may be ruptured. If less violent force is applied, some funiculi may survive. The longitudinal extent of the lesion is always great, reaching 2 to 5 centimetres in the rabbit.