In 1936 Tomesco (1) and his co-workers described changes in the crystallization of sodium chloride produced by the addition of small amounts of cerebrospinal fluid to 0.8 per cent. saline. A drop of *8 per cent. NaCl solution dried on a microscope slide at 75° C. produces a thin circumference of crystals surrounding an empty space. If normal C.S.F. is added in proportions of 1 C.S.F. to 20, 40 or 60 parts saline the central empty space is replaced by a thin translucent film of crystals, which in the higher dilutions begins to show lacunae. In a dilution of 1 in 120 this translucent film is reduced to a narrow strip along the inner margin of the circumference. Microscopically the translucent area is found to consist of concentric circles, feather- or spear-shaped crystals, parallel lines, needles, etc., well organized in the low dilutions, but not organized in a dilution of 1 in 120. This is regarded as the normal crystal picture.