438 BACTERIOLOGICAL CHEMISTRY 



Mid-piece. — Euglobulin ; heat labile ; carries 60 to 

 80 per cent, of C3 and to 30 per cent, of C4 ; 

 constitutes 0-6 per cent, of total serum protein ; 

 contains about 3 per cent, of carbohydrate ; 

 completely adsorbed in complement fixation and 

 lytic reactions. 



Third Component. — Mainly associated with mid- 

 piece ; heat stable ; specifically adsorbed by 

 zymin or zymosan. 



Fourth Component. — Associated with end-piece ; not 

 adsorbed by zymin ; specifically inactivated by 

 ammonia ; heat stable ; necessary for complement 

 fixation and lytic reactions but not for opsonin 

 action ; possibly a carbohydrate. 



Complement, however, is probably even more complex 

 than this summary suggests ; the separation of these 

 components is not always sharp and others may be present. 

 For instance, complement can be reversibly inactivated 

 by oxidation with iodine ; reduction with ascorbic acid 

 or glutathione restores the activity. The activity of 

 oxidised complement can also be restored by the addition 

 of complement from which the third and fourth com- 

 ponents have been removed ; the component inactivated 

 by oxidation is therefore different from C3 and C4. The 

 activity of complement is also lost on dialysis, but is 

 restored by addition of a small quantity of the dialysate. 

 Since the activity of complement devoid of C3, C4 and 

 the oxidisable component is not restored by the dialysate 

 whilst the activity of dialysed complement can be 

 restored by the addition of dialysate from complement 

 previously deprived of these components, the dialysable 

 component must be different from them. 



In view of this complexity it has been suggested that 

 complement is not a definite substance but is really a 

 particular state of the serum colloids, a state which can 

 be very easily upset even by such means as mechanical 



