The interstitial cell and its place in the concept of the autonomic ground plexus

1. The autonomic interstitial cells have been studied in the toad small and large intestine and guinea‐pig taenia coli by means of both the light and electron microscopes. The guinea‐pig superior cervical ganglion has also been examined. 2. Apart from muscle cells, neurons and Schwann cells, at least one other cell type has been observed. These cells have been designated connective tissue cells on the basis of their gross form, fine structure and relation to other cells. In many respects they resemble fibroblasts and macrophages. 3. These cells are in close relation to nerve fiber bundles and smooth muscle cells. They often form a complete sheath around bundles of axons and Schwann cells. Many of the processes of the connective tissue cells lie in grooves on the surface of the muscle cells; the distance between apposing cell membranes is about 200 Ä. 4. The processes of the connective tissue cells often interdigitate with each other in a most complex manner, the opposing cell membranes being about 200 Ä apart. Such a close relationship would appear with the light microscope to be a fusion forming a syncytium. 5. Observation with the light microscope on the terminal ramifications of the autonomic nervous system where small bundles of fine axons are enclosed by connective tissue cells could give rise to the impression that they contained “neurofibrils.” 6. It is suggested that the term autonomic interstitial cell covers a number of cell types which have been confused. The cells designated connective tissue cells along with Schwann cells have between them the characteristics of the autonomic interstitial cells as described by previous workers. Cajal's original description of sympathetic interstitial cells was actually a description of connective tissue cells.