Nissl's substance is mainly

Nissl Substance - The cytoplasm shows the presence of a granular material that stains intensely with basic dyes; this material is the Nissl substance (also called Nissl bodies or granules). When examined by EM, these bodies are seen to be composed of rough surfaced endoplasmic reticulum. The presence of abundant granular endoplasmic reticulum is an indication of the high level of protein synthesis in neurons. The proteins are needed for maintenance and repair, and for production of neurotransmitters and enzymes. REF : Inderbir Singh's Textbook of Human Histology, seventh edition, pg.no.,164.