84 



which the agglutinating serum was produced. With certain 

 agglutinable strains, however, the amount of agglutinin removed 

 is insufficient to lower appreciably the titre of the serum for the 

 homologous strain : in such cases it is usually possible to show 

 that the titre for another related strain is partially or completely 

 abolished. The Table 5 illustrates the effects of contact with 

 various agglutinable strains on the agglutinating power of the 

 serum. 



Table 5. — Absorption of Agglutinin. 



4 mg. moist culture mixed with each 1 c.e. of 1/50 dilution of 

 Serum (V. B.S. 6). 



* A sample of serum taken before the final titre was attained. 



It is evident from Table 5 that the strains L 1a and L 36* 

 contain considerable quantities of the same antigen as is contained 

 in B.S. 6, the strain with which the serum was produced. 



In addition, it may be noted that, though Lister 3 removes only 

 a trace of the B.S. 6 agglutinin (agglutination at 1 in 800 barely 

 complete), it reduces by half the titres for L 1a and L 18, showing 

 that part of the antigenic complex responsible for the agglutina- 

 tion of these two strains is present in Lister 3 ; further, absorption 

 with S 1 does not reduce the agglutinin for the homologous strain 

 B.S. 6 but removes all the agglutinin for Lister 3 and a consider- 

 able part of that for L Ia and L 18, i.e., the strains S 1, Lister 3, 

 L Ia, and L 18 have certain antigenic components in common. 



Speaking generally, one may say that the relationships between 

 strains indicated by agglutination reactions are confirmed by 

 their powers of removing agglutinin, and that, therefore, these 

 relationships depend on similarities in antigenic structure. 



* (L 36 is a strain isolated from the same case of lobar pneumonia as 

 L 36a : the former came from the sputum, the latter from the necrotic 

 lung post mortem about three weeks later. The former is a III strain, the 

 latter one of the typical II strains.) 



