Studies in histochemistry: L. Measurement of water in histological structures by a direct microradiographic method

The measurement of water in histological structures was investigated using rat liver, kidney and gastric mucosa. Measurements on liver and kidney, based on differences between mass per unit area in the fresh-frozen and dry states, when both were determined by X-ray absorption, gave results which were too low, probably because of appreciable water loss from the fresh-frozen sections of tissue during microtomy and X-ray photography, even at − 13 °C. Nevertheless, this loss of water was not great enough to reveal structural details in historadiograms of the fresh sections which showed no discernable cellular structure. It was possible to obtain reliable values for mass per unit area in fresh-frozen sections by quick direct weighing of groups of sections, in some cases a small correction was required for loss of water with time. The values could also be obtained from the measurement of specific gravity of pieces of fresh tissue at −18 °C, although this procedure is not as simple as the former. From these values and those for mass per unit area in the dry state as given by X-ray absorption, both the mass of water per unit area and the per cent water in histological structures were found. Incidentally, corrections that apply to the X-ray measurement of dry sections of tissue were elaborated.