Measurement of experimentally induced brain swelling and shrinkage.

White et al. (I, 2) have measured changes in brain volume in cats by careful determinations of the volume of the brain and of the cranial cavity. The normal difference between these two volumes is about IO per cent and variation from this figure represents swelling or shrinkage of the brain. This method is difkult, and could hardly be applied after craniotomy. Assuming that changes in brain volume are due to changes in water content, and that the percentage of dry matter in the brains of normal animals is constant, then a difference from normal in the percentage dry weight of the brain of an experimental animal must be a measure of a change in volume. The swelling or shrinkage may be simply calculated without any need to determine the actual volume of the brain. If W and D are respectively the fresh and dry weight of the brain of a normal