Differential staining of different types of peripheral nerve and muscle

We modified Ungewitter's (1951) and Beermann and Cassens' (1976) non-selective silver methods for peripheral nerve axons and their terminals by lengthening the time for the prestaining treatment of sections, adjusting the times of various stages of the staining procedures and selecting reagents with minimal chloride and sulphate impurities. These methods were applied to Bouin's fixed material embedded in wax with serial sections up to 100 micron thick, cut longitudinally. The Ungewitter modification stained sensory axons and their terminals very well but failed to give good impregnations of motor fibres. In addition, it marked intrafusal muscle fibres with a peppery silver deposit while sparing extrafusal fibres. The Beermann and Cassens method yielded excellent details of motor axons and their terminals but results were very poor on sensory fibres. Both sensory and motor methods worked regardless of whether the neural elements were mature, regenerating, or neonatal. Both methods consistently yielded pale backgrounds in these thick sections.