Positive colloidal-gold reactions in the cerebrospinal fluid of patients with multiple sclerosis have been reported as occurring in 29-81 % of fluids examined by various investigators (Freedman & Merritt, 1949). Coagulation of the colloidal gold has been shown to be associated with the y-globulin fraction (Kabat, Moore & Landow, 1942). The concentration of y-globulin in cerebrospinal fluid was determined immunochemically by Yahr, Goldensohn & Kabat (1954), who report an increase in 66-5 % of the multiple-sclerosis cases studied. The mechanism of several flocculation tests, including the colloidal gold at pH 7-8 and 6-6, was studied by Maclagan & Bunn (1947), using normal and hepatitis serum fractions; they found that albumin and a-and p-globulins protected the colloidal gold and that y-globulin brought about its coagulation.Serum diluted to 0-03 % protein gives a very strongly positive colloidal-gold reaction (Press, 1955), whereas a normal cerebrospinal fluid, having approximately the same concentration of albumin and globulins, gives a negative colloidalgold reaction; this is suggestive of a qualitative difference between the protein fractions of cerebrospinal fluid and serum.In the present study, the proteins of normal and pathological cerebrospinal fluids and normal sera have been compared both quantitatively and qualitatively. Cerebrospinal fluids and sera were analysed electrophoretically, and the percentage of y-globuhn in the cerebrospinal fluids was compared with the type of the colloidal-gold reaction. Albumin and ac-, 9and y-globulins have been isolated from sera and cerebrospinal fluid and the effect of these fractions on the collidal-gold reaction studied and their sedimentation constants determined.Partial fractionations of cerebrospinal-fluid yand f-globulins were performed in the ultracentrifuge and the effect on the colloidal-gold reaction of the more slowly sedimenting fraction was examined. The chemical nature of this 'slow' component from both fiand y-globulin was determined. Cerebrospinal-fluid y-globulin was also fractionated with 18 % sodium sulphate, and the sedirnentation constant of the fractions and their effect on the colloidal-gold reaction were determined.
EXPERIMENTALMaterials Veronal buffer 1. This buffer (pH 8-6, 1=0-1), which was used for micro-electrophoresis, contained 0-1 M sodium veronal and 0-02M veronal.Veronal buffer 2. This buffer (pH 8 6, I =0-0375), which was used for continuous paper electrophoresis, contained 0-0375m sodium veronal and 0 0075m veronal. Phosphate buffer 1. This buffer (pH 74) was made by mixing 48 ml. of KH2PO4 (0-067m) and 202 ml. of Na2HPO4 (0.067m).Phosphate buffer 2. This buffer (I = 0-2, pH 7 45) contained 0-0142M-Na2HPO4, 0 0025M-KH2PO4 and 0 1M-NaCl. Sodium sulphate (27 %, w/v) in phosphate buffer pH 7-8. For this solution 270 g. of anhydrous Na2SO4, 6 g. of K2HPO4 and 0 488 g. of KH2PO4 were made up to 1 1. at 370* Dextran. Initially, a supply of 20 % Dextran was available, approximate molecular weight 40000 (kindly supplied by Dextran Co. Lt...