When the tissue is slowly cooled, ice first forms between cells. The growing ice crystals increase the concentration of solutes in the remaining liquid around them, causing water to be pulled from the cell through a process called osmotic dehydration. If cryoprotectants are present, the freezing point of the unfrozen solution drops sooner and faster, limiting the total amount of ice that forms. As the temperature drops below -40°C, the cryoprotectant concentration becomes so high in the remaining unfrozen solution that ice stops growing. Cells survive suspended in the residual unfrozen liquid between ice crystals. As the temperature drops below about -100°C, this unfrozen solution containing the cells becomes a glassy solid. This is called vitrification.