361chromism is identical to the first-order term of the present theory LEq. (35) j. Hoffmann's results are contained, as an approximation, in the present theory.For completeness, we point out discussions of the hypochromism problem by McLachlan and Bal1. , " Fowler, ' and Bullough, " whose conclusions are in general agreement with ours.The theory, therefore, contains nothing which is basically new, but does serve to coordinate previous theories under one "theoretical roof". Ke feel that, because of the generality, directness, and completeness of the approa, ch, the use of linear response (retarded) Green's functions will point the way to better approximation methods.The same method should be readily applicable to other optical phenomena, besides absorption, such as rotatory dispersion and molecular crystal reQection.This article presents a simplified treatment of the high density, collisionless, free-electron gas, based on the ideas of a wave number and frequency-dependent conductivity and dielectric constant. The formalism is applied to solve a number of problems: the screening of the electrostatic potential of a foreign point charge placed in the electron gas, the rate of energy loss of a charged particle moving through the electron gas, plasma oscillations, the reflection of electromagnetic waves from the electron gas, and ultrasonic attenuation in metals due to the interaction of the sound waves with the conduction electrons. In a Anal section it is indicated how the methods may be generalized. Explicit expressions for the conductivity of the electron gas are obtained in an appendix. ' J. Lindhard, Kgl. Danske Videnskab. Selskab, Mat. -I'ys.

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BackgroundAn adequate renal biopsy is essential for diagnosis and treatment of medical renal disease.ObjectiveWe evaluated two initiatives to improve adequacy of renal biopsy samples at our centre.DesignRetrospective determination of renal biopsy adequacy.SettingQueen Elizabeth II Health Sciences Centre.PatientsPatients undergoing medical renal biopsies.MeasurementsRenal biopsy adequacy.MethodsThe first initiative was to restrict the performance of biopsies to a smaller group of radiologists and to include a comment on biopsy adequacy in every pathology report. The second initiative was to introduce on-site adequacy assessment by a medical laboratory technologist. Native renal and allograft biopsy adequacies were calculated for three periods: 1) baseline, October 2005 to September 2006; 2) after implementation of the first initiative, January 2007 to September 2011; and 3) after implementation of the second initiative, October 2011 to September 2012. A subset of native renal biopsies was examined to determine if there was a relationship between adequacy and number of passes.ResultsThe percentages of adequate native renal biopsies during the first, second, and third periods were 31%, 72% and 90%, respectively. This represents a significant increase (40%, p < 0.0001) in adequacy following the first initiative, and another significant increase (18%, p = 0.0003) following the second initiative. The percentages of adequate renal allograft biopsies during the first, second, and third periods were 75%, 56% and 69%, respectively. These changes in adequacy were not statistically significant. In the subset of native renal biopsies examined, a biopsy comprising more than three cores was not associated with increase in adequacy.LimitationsThe most important limitation is the lack of generally accepted and applied adequacy criteria limiting generalizability of our findings.ConclusionsRestricting the performance of biopsies to subspecialist operators, including an adequacy statement in the renal biopsy report and on-site adequacy assessment were effective in significantly improving native renal biopsy adequacy. This improvement appeared unrelated to an increase in the number of passes taken with a biopsy needle. Neither initiative improved the low adequacy of allograft biopsies.

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