Abstract
Change in total dry mass following extraction with petroleums ether, as measured by X-ray absorption, was used to determine lipid in each histological zone of dried fresh-frozen microtome cross-sections of adrenal glands of male albino rats. Although the area of measurement was 1.1 µ2, and the data were given in units of 10–12 gm/µ2, the differences in dry mass per unit area in this material were not great enough to permit useful analytical resolution below the histological level. The data were in general agreement with those obtained from differences in mass by direct weighing of a series of whole dried fresh-frozen microtome sections which had been cut to segregate the various zones. The particular advantage of the X-ray method is that it permits determination of the lipid in situ in each of the histological zones of the gland in a single microtome cross-section, and the pair of microradiograms taken, before and after extraction, provides a permanent record from which measurements can be obtained subsequently at any time. Mean values found for total lipid, as percent of total dry mass, in adrenal zones of untreated rats were 12, capsule; 17, glomerulosa; 36, fasciculata; 36, reticularis; and 19, medulla.