Correspondence re: R. Grant Steen et al., In Vivo 31P Nuclear Magnetic Resonance Spectroscopy of Subcutaneous 9L Gliosarcoma: Effects of Tumor Growth and Treatment with 1,3-Bis(2-chloroethyl)-1-nitrosourea on Tumor Bioenergetics and Histology. Cancer Res., 48: 676–681, 1988