ANTIGENS. HAPTENS, ANTIBODIES. ETC. 431 



as shown by the fact that such digested antibody inliibits 

 normal toxin-antitoxin flocciilation. The euglobulin of 

 Types I and II antipneumococcus horse sera can be 

 digested by pepsin to give smaller active molecules having 

 a sedimentation constant of 5-2x10"^^ cm. per second 

 per dyne, corresponding to a molecular weight somewhat 

 less than 100,000, and able to combine with twice as 

 much specific poh^saccharide per mg. of antibody nitrogen 

 as the original antibody. 



The introduction of azo-compounds or of iodo -groups 

 or the action of formaldehyde lowers the titre of an 

 antiserum, but is said to sharpen the specificity. Eagle 

 and his co-workers have shown that coupling pneumo- 

 coccus antiserum with diazotised atoxyl has a differential 

 effect on the reactions of the antiserum ; the power of 

 agglutinating bacteria and of precipitating the specific 

 polysaccharide ma}^ be lost, but not the power to protect 

 mice against infection. The action of the azo -compound 

 proceeds at different velocities for the different mani- 

 festations of the antibody, but a sufficiently long contact 

 with the reagent causes a complete loss of all the anti- 

 body reactions. With the pneumococcus antiserum the 

 precipitin reaction is lost before the agglutinating power, 

 protective properties or ability to fix complement. In 

 the case of diphtheria antitoxin the flocculating property 

 is lost before the power to neutralise toxin. These 

 effects are illustrated in Table 30. The addition of 1 

 part of formalin to a thousand parts of antiseiiim brings 

 about similar effects. It is suggested that the addition 

 of just enough formaldehyde to prevent aggregation 

 increases the solubility of the antibody so that it no 

 longer i^recipitates at the normal conditions of /jH of 

 serum. 



In Type I pneumococcus antiserum replacement of a 

 hydrogen atom in the amino group by acetyl, by the 

 action of ketene, reduces its activity, whilst the action of 

 formaldeh^'de causes loss of specificity. Esterification 



