1. An apparatus for determining the concentration of an organic blood analyte in a body tissue sample, comprising: (a) means for irradiating the sample with incident radiation containing a plurality of distinct, nonoverlapping spectral regions within the infrared spectrum, wherein each of the spectral regions encompass a range of wavelengths between approximately 1100 and 5000 nanometers; (b) means for collecting reflected radiation emerging from tie sample and directing said reflected radiation into a beam path; (c) adjustable filter means disposed in the beam path, wherein said adjustable filter means attenuates the intensity of radiation in the beam path; (d) principal analyte filter means capable of receiving radiation emerging from the adjustable filter means, and selectively passing discrete wavelengths therefrom, wherein said discrete wavelengths are specifically correlated with the concentration of the analyte; (e) second filter means capable of receiving the discrete wavelengths emerging from the principal analyte filter means and attenuating the intensity of said wavelengths; (f) detection means for receiving the attenuated wavelengths emerging from the second filter means; (g) means for converting the detected wavelengths into a signal representative of the intensity of said wavelengths; and (h) means for correlating the signal obtained in step (g) to determine the concentration of the analyte.