1. Federal Register, 37, No. 221, part 2 (1972).
2. Motor Vehicles (Construction and Use), Regulation 33A (HMSO, 1973).
3. Holland, R. A. B., Ann. N. Y. Acad. Sci., 174, 154–171 (1970).
4. Robinson, E., and Robbins, R. C., Ann. N. Y. Acad. Sci., 174, 89–95 (1970).
5. Waller, R. E., Commins, B. T., and Lawther, P. J., Br. J. industr. Med., 22, 128–138 (1965).