It is known that a large part of the vitreous fluid is water bound by capillary attraction and ready to escape when the vitreous is injured. Only a small amount of the fluid is colloidally bound to the substrate of the fibrils as hydration water. These conditions explain the primary difference in the results of volumetric investigations with varying technics. For reasons mentioned in a previous paper1 the vitreous should be examined in toto. Important as observations on the expansion of isolated fibrillar substance may be, it is of course not feasible to draw conclusions about volume changes of the vitreous from them. In the more frequently used method of recent investigators, pieces were cut from different parts of cattle vitreous and were found to decrease steadily in a physiologic milieu. This decrease, probably caused by the uncontrolled escape of capillary fluid, was prevented in our experiments by avoiding