52 D. A. L. DAVIES 



5{xg./ ml. could be obtained in fractions sedimented at intermediate 

 speeds, much activity was left in adjacent fractions. In any case, 

 as the active sediments gave only moderately stable suspensions 

 in BS, their differing particle sizes would be likely to affect their 

 measurable activity. Fractional centrifuging was therefore 

 subsequently omitted and advantage taken of the sedimentation 

 to remove all soluble components by centrifuging four times 

 from BS, twice from 0-9 per cent salt, and then twice from 

 water. Tests by agar diffusion now showed no significant 



* Carbohydrate. 



t Dilution giving haemagglutination inhibition divided by I GO. 



^ Tartrate gradient fractions. 



reaction for components of normal serum. The activity at this 

 stage was generally 10-20 [ig./ml., and analytical figures are 

 shown in Table III. 



Advantage having been taken of solubility and of mass, the 

 increase in the proportion of lipid with increasing activity 

 suggested the use of density gradients. Potassium tartrate was 

 chosen on account of its low viscosity (McCrea, Epstein and 

 Barry, 1961). The centrifuged precipitate (-^300 mg.) was 

 suspended in water at 2 per cent concentration, centrifuged for 

 20 minutes at t,ooo^ to remove dirt, and i ml. volumes layered 



