In the preceding paper it has been shown that the general or local atrophy of the brain occurring in chronic insanity is very largely due to loss of white matter. It seemed to be of interest to determine what chemical changes accompanied this shrinkage in the size of the brain. As a preliminary to an examination of the complex substances of which brain matter is composed, it was necessary to investigate the proportion of water to solids, as the figures obtained in this way are of the highest importance in regard to the interpretation of the results obtained by chemical methods. The examination of the various portions of brain tissue for the amount of water was therefore proceeded with as a routine measure. The whole of the grey or of the white matter, as the case might be, from each of the five portions, obtained as described in the preceding paper, was spread on glass plates in as thin a layer as possible and carefully weighed. The plates were then placed in a Hearson electric drying oven, the temperature of which was maintained at about 90° C. A current of dry hot air was passed into the oven from a fan attached to a small motor. After fifteen to twenty hours' exposure the plates were removed from the oven, and the solid material which remained was carefully and completely scraped off. It was then allowed to cool to room temperature and weighed. The material was returned to the oven for some hours, again removed and allowed to cool. This procedure was continued until the material attained a constant weight at room temperature. The percentage of water in each sample was then calculated.