1. Herniated lumbar intervertebral discs commonly compress single nerve roots, and present associated dermatome hypalgesia in the lower extremity, which is accurately diagnostic of the location of the lesion.

2. A new dermatome chart of the lower extremity is presented, based upon hypalgesia from proved single nerve-root loss. These findings are in disagreement with the common dictum that loss of a single nerve root produces no loss of sensation.

3. The nerve root most commonly compressed by herniated intervertebral disc is the first sacral nerve root. Recognition of the syndrome of lesions of the first sacral nerve root, with its characteristic dermatome hypalgesia and loss of the ankle jerk, removes any extraspinal lumbar pathology as a possible cause, as this nerve root is entirely intraspinal until its exit through the first sacral foramen.

4. Subjective and objective numbness and reflex loss are organic neurological signs, not explainable from any possible reflex reference from obscure distant pathology. Numbness over the distribution of a single nerve-root dermatome necessitates a lesion directly and discretely involving that root.

5. The common occurrence of pathology of the fifth and fourth lumbar discs, leading to later herniation, should be considered more often as a possible explanation of early attacks of low-back pain; and manipulative treatment should be directed to possible reduction of this beginning herniation.

6. Roentgenograms of the lumbar spine should be directed to the disc indicated by the finding of unilateral single dermatome hypalgesia. Other pathology seen in roentgenograms, not directly related to that nerve root, should not be used to explain this organic neurological finding.

7. A conservative attitude should be maintained in surgery of the herniated disc, for in many early cases improvement occurs without surgical interference; however, with or without operation, these patients present some permanent disability which requires back protection.

8. Spine-fusion operation is not often indicated in herniated disc, because of both the unreliability of preoperative selection of cases which will require it, and the recognized imperfect results of this time-consuming procedure.

9. Deliberate section of a nerve root sometimes is warranted and effective to relieve persisting single nerve-root pain after an operation for a herniated disc. The nerve is identified by its dermatome hypalgesia.