ANTIBODIES TO PNEUMOCOCCUS 417 



fuge, Heidelberger, Pedersen, and Tiselius observed that in the 

 case of immune rabbit serum the specific antibody was produced 

 from the principal globulin component, while in the horse the anti- 

 carbohydrate for Type I Pneumococcus is developed from an 

 otherwise minor component. The isoelectric point of the protein 

 representing the pneumococcal antibody of the rabbit was deter- 

 mined as approximately pH 6.6, whereas the isoelectric point of 

 the immune protein from horse serum was as acid as pH 4.8. That 

 the molecule of the protective antibodies as elaborated by the two 

 animal species is of different size is also evident from the work of 

 Goodner, Horsfall, and Bauer. 689 When Type I antipneumococcic 

 rabbit serum was filtered through an ultrafilter of the type de- 

 scribed by Bauer and Hughes, 90 no appreciable specifically pre- 

 cipitable protein passed through a membrane with an average pore 

 diameter of one millimicron. A 13.8 millimicron filtrate con- 

 tained 11.9 per cent of the total specifically precipitable protein. 

 Slightly greater amounts were recovered as the pore sizes were in- 

 creased up to 73 millimicrons, at which point the curve rose 

 sharply until at 102.5 millimicrons the filtrate contained 86.6 per 

 cent of the total antibody. With antipneumococcic horse serum, 

 the smallest pore permitting the passage of antibody was 45.2 

 millimicrons. Between 73 and 102.5 millimicrons the curve rose 

 steeply until at the latter porosity 76.7 per cent of the antibody 

 was recovered. With a concentrated preparation of Type I anti- 

 pneumococcic horse serum the end-point was relatively sharp, no 

 antibody being recovered at 150.4 millimicrons, while 100 per 

 cent was found in the filtrate at 188 millimicrons. The authors 

 decided that in general it might be assumed that the smallest spe- 

 cific antibody of antipneumococcic rabbit serum corresponds to a 

 pore size of 11 millimicrons, the smallest in horse serum to a size 

 of 44 millimicrons, while both horse and rabbit antibodies have 

 large specific aggregates corresponding roughly to a pore size of 

 88 millimicrons. Furthermore, the antibody of concentrated horse 

 serum requires a pore size of approximately 176 millimicrons. 



