The “Third Component” or Heat-Stable Factor of Complement

Abstract

THE separation of complement by various methods of protein precipitation into mid-piece and end-piece, or globulin and albumin fractions, has been well established. Ferrata [1907] and Brand [1907] effected the separation by dialysis, Liefmann [1909] by saturation with C02, and Sachs and Altmann [1909] by the use of dilute hydrochloric acid. Although the two fractions may be present as a single component in the original serum, the method of separation by -dialysis appears to support the view that they are separate entities from the first; other evidence is in favour of some loose chemical or physical union between them. On the other hand, Browning and Mackie [1913] contend that the so-called mid-piece and end-piece Ifractions do not represent constant entities, basing this view on inability to get perfect separation on every occasion by the C02 method of Liefmann and on the results given by their ammonium sulphate separation. It seems, however, too exacting to expect the simple methods of protein separation to give results comparable with those of inorganic methods, although our experience of these methods, especially Liefmann's, has been rather more -satisfactory. We find in almost every experiment that the separate fractions give practically no complement action whatever even when quantities corresponding to four times the minimum haemolytic dose (M.H.D.) are used, whereas, when combined, they show practically the same activity as the original complement.