Hirsch, Carl, et al. “Biophysical and Physiological Investigations on Cartilage and Other Mesenchymal Tissues VI. Characteristics of Human Nuclei Pulposi During Aging”. Acta Orthopaedica, vol. 22, no. 1-4, Jan. 1952, pp. 175-83, doi:10.3109/17453675208989005.