418 BIOLOGY OF PNEUMOCOCCUS 



Goodner, Horsfall, and Bauer drew attention to the fact that the 

 figures given are multiples of 11, which corresponds to the value 

 of 11 to 12 millimicrons determined by Elford and Ferry 353 for 

 the isolated form of normal horse pseudoglobulin. 



Recent observations on the molecular size of pneumococcal anti- 

 body in immune rabbit serum, in immune horse serum, and in con- 

 centrated antibody solution are of importance not only in con- 

 nection with differences in the characters of antibody as produced 

 in animals of different species, but in emphasizing the range in sur- 

 face area of the different types of antibody. Gram for gram, the 

 pneumococcal antibody from the immune rabbit, because of its 

 smaller molecular size and therefore its greater surface area, 

 should exhibit greater combining power for homologous antigen 

 than the antibody of the larger molecule of immune horse serum 

 and that of the still larger aggregate present in concentrated anti- 

 pneumococcic serum. 



THE SEPARATION OF ANTIBODIES FROM IMMUNE SERUM 



Inasmuch as the concentration and purification of pneumococ- 

 cal antibodies will be described in detail in Chapter XV, only the 

 principles involved in the separation of specific substances from 

 immune serum will be dealt with in the present chapter. Gay and 

 Chickering 508 " 9 took advantage of the particulation that takes 

 place when cellular substances of Pneumococcus are brought into 

 contact with homologous immune serum. From the antigen-anti- 

 body precipitates the antibody was then recovered by the use of 

 suitable physical and chemical agents. The method was adopted, 

 with modifications, by Huntoon and his associates 665 " 6 ' 668 " 9 and the 

 use of specific precipitates has been developed as furnishing a 

 source of pneumococcal antibody. Another basic method is founded 

 on the relative insolubility of the immune proteins in water at their 

 isoelectric point, as well as their insolubility in water in the ab- 

 sence of electrolytes. The use of protein coagulants such as am- 

 monium and sodium sulfates, so valuable in the concentration and 



