ly. The oxygen fugacity (/02) of the experiments was not buffered externally. However, /02 calculations based on biotite-sanidine-magnetite-H20-02 equilibrium [D. R. Wones, Kozan Chishitsu 31, 191 (1981)] yield /02 values 1.5 to 2 log units above the nickel-nickel oxide buffer. This is consistent with the estimated f02 conditions of natural epidote-bearing magmas {6, 16). Quenched experimental charges were sectioned longitudinally, polished, and examined with reflected-light microscopy and backscattered electron imaging. Rim widths were measured with an optical microscope equipped with a graduated ocular lens; the rim widths reported are the average of 20 to 30 measurements. Rim width data are as follows: experiment Ep-10, t = 51.17 hours, rim width = 2.74 ± 0.9 fjim; experiment Ep-12, t = 141.20 hours, rim width = 4.95 ± 0.8 fjtm; and experiment Ep-11, t = 378.78 hours, rim width = 8.18 £ 1.3 fjtm. 9. D. C. Rubie and A.

By means of optical pumping with laser light it is possible to enhance the nuclear spin polarization of gaseous xenon by four to five orders of magnitude. The enhanced polarization has allowed advances in nuclear magnetic resonance (NMR) spectroscopy and magnetic resonance imaging (MRI), including polarization transfer to molecules and imaging of lungs and other void spaces. A critical issue for such applications is the delivery of xenon to the sample while maintaining the polarization. Described herein is an efficient method for the introduction of laser-polarized xenon into systems of biological and medical interest for the purpose of obtaining highly enhanced NMR͞MRI signals. Using this method, we have made the first observation of the timeresolved process of xenon penetrating the red blood cells in fresh human blood-the xenon residence time constant in the red blood cells was measured to be 20.4 ؎ 2 ms. The potential of certain biologically compatible solvents for delivery of laser-polarized xenon to tissues for NMR͞MRI is discussed in light of their respective relaxation and partitioning properties.