416 BIOLOGY OF PNEUMOCOCCUS 



The experiments strongly support the idea that the Type I anti- 

 body is associated with the molecule having 



s=16X 10 13 



Furthermore, Biscoe, Pickels, and Wyckoff obtained the same 

 measurement for molecules of antibodies against other types of 

 pneumococci. Speculating on the relation between pneumococcal 

 antibody and specific immune protein, Wyckoff concluded: "Since 

 this is a molecular species that appears in appreciable quantities in 

 horse serum only when it has become antipneumococcic, two possi- 

 bilities suggest themselves. It is conceivable that during immu- 

 nization this globulin is made or freed in excess in order that there 

 may be plenty of it present to fix all the antibody activity that 

 may develop . . . and the alternate, that the globulin is the anti- 

 body." The results of investigations of this nature are highly sug- 

 gestive, and the method promises to yield valuable information 

 concerning this abstruse but important question. 



Differences in the nature of the protective antibody in anti- 

 pneumococcic rabbit serum and in that in antipneumococcic horse 

 serum have been demonstrated by Chow. 224 In horse serum, the an- 

 tibody in the pseudoglobulin fraction soluble at pH 5.5 was com- 

 pletely precipitated when the reaction of the solution was ad- 

 justed to pH 7.6. From the corresponding fraction of the immune 

 rabbit serum no trace of precipitate was obtained. Furthermore, 

 in the case of immune horse serum, the main portion of the anti- 

 body was concentrated in the pseudoglobulin fraction, whereas the 

 opposite was found to be true with the immune rabbit serum, that 

 is, the euglobulin fraction apparently contained the major portion 

 of the antibody.* 



Another difference in the antibodies present in antipneumococcic 

 rabbit and horse serum lies in the size of the molecule of the two 

 substances. In experiments involving the use of the ultracentri- 



* A difference in the phosphatid molecules linked with the globulin in the 

 case of antibodies from the horse and rabbit has been mentioned in the foot- 

 note on page 381 of this chapter. 



