428 BACTERIOLOGICAL CHEMISTRY 



enzymes aiul ))y denatiiratioii ; IM) to 1)5 per cent, uf the 

 protein (0-002 to 0-006 mg. of nitrogen per unit) in these 

 preparations could be precipitated by the soluble specific 

 polysaccharide. Heidelberger and Kendall dissociated 

 similar precipitates with 15 per cent, sodium chloride 

 and recovered the antibody by dialysis. The remaining 

 undissociated precipitate was decomposed by barium 

 hydroxide or barium chloride, which precipitate the 

 Types I and III specific polysaccharides, leaving the 

 antibody in solution ; they succeeded in removing all 

 the inactive protein in this way, 95 to 100 per cent, of 

 the nitrogen in the final solutions being precipitated by 

 the polysaccharides. 



The Properties of Antibodies. — The size of the anti- 

 body molecule is about the same as that of normal 

 serum globulins, as is shown by sedimentation rates in 

 the ultra-centrifuge and by filtration through membranes 

 of known pore size. Normal human serum globulin has 

 a molecular weight of about 170,000, that of the rabbit 

 about the same and that of the horse has two fractions, 

 one with molecular weight about 170,000 and the other 

 with molecular weight about 900,000. Antibodies to the 

 pneumococcus in horse serum are associated with the 

 heavy globulin fraction and have molecular weight 

 about 900,000, and a diameter about 44 m/x. The rabbit 

 antipneumococcus globulins have a diameter about 

 11 m/x and molecular weight about 170,000. This dif- 

 ference between the two antibodies is not restricted to 

 size ; the horse antibody is said to be associated with 

 the pseudoglobulin and the rabbit antibody with the 

 euglobulin. A further difference lies in their lipoid 

 content ; if the antisera are extracted with fat solvents, 

 about 1-3 per cent, of lipoid is removed and they no 

 longer give precipitin reactions, although their protective 

 effect in mice is unaltered ; the precipitin properties 

 can be restored by the addition of lecithin to horse 



