ANTIBODIES TO PNEUMOCOCCUS 415 



Further information concerning the intimacy existing between 

 pneumococcal antibody and immune serum globulin has come from 

 analyses of normal and antipneumococcic serum by means of the 

 ultracentrifuge of Svedberg 1369 and a modified machine described 

 by Biscoe, Pickels, and Wyckoff (1936). 119 Employing the latter 

 apparatus, Biscoe, Hercik, and Wyckoff 118 determined that in con- 

 centrates of Type I antibodies the proteins consist mainly of mole- 

 cules with a sedimentation constant of about 



16 X 10 13 cm. sec" 1 dynes" 1 . 



This finding, taken with the presence of similar molecules in uncon- 

 centrated antipneumococcic horse serum and their complete or al- 

 most complete absence from normal serum indicates that these 

 molecules are the real bearers of antibody activity. Further sup- 

 port of the view is supplied by the observation of Heidelberger, 

 Pedersen, and Tiselius 629 that after ultracentrifugation the spe- 

 cific antibody from serum from a horse immunized with Type I 

 polysaccharide and a sample of concentrated Type I antipneumo- 

 coccic serum (Felton) showed homogeneous sedimentation, with 

 the following sedimentation constant: 



* 20 = 17.2 X 10 13 



The sedimentation constant of normal globulin from mammalian 

 serum is: 



s 20 = about 7 X 10" 13 



By applying the method to concentrated preparations of Type 

 I antipneumococcic serum, Wyckoff 1555 found that the only pro- 

 tein molecules in the bottom layers of the fluid were those with 



s= 16 X 10 13 



Small amounts of light molecules, which in each concentrate ac- 

 counted for roughly 15 per cent of the total protein content, were 

 those of the principal serum globulin with 



s = 7X 10 13 



