11 



0-000 001 c.c. killed the control; but the serum of these animals 

 had no protective power and showed no trace of immune bodies. 

 Possibly, they thought, there might be a fundamental difference 

 between active and passive pneumoccocus immunity; or, at 

 any rate, in resistance and recovery " there may be other factors 

 <{ concerned than the humoral ones." They considered that the 

 action of immune serum did not depend entirely either on its 

 agglutinative or on its bacteriotropic power. " The protection 

 " of small animals undoubtedly reproduces more accurately the 

 " part which the serum plays in recovery from natural infection, 

 " as seen in the human patient, but even here the conditions are 

 a not identical . . . The production of active immunity is 

 " attended with little difficulty and the form of antigen, so far as 

 " we know, is not of great importance, but when we come to the 

 " question of the production of humoral immunity, especially of 

 " the highest grade, this factor may be of the greatest importance.'* 

 Virulence for the mouse and rabbit did not give much clue to the 

 virulence of a strain for man. It was not known whether it was 

 important or not for the cultures to be of high virulence when 

 used for producing immune sera. They observed that Neufeld 

 and his colleagues said that it was, but did not give protocols to 

 prove it. 



Inhibitory Properties of Immune Serum. 

 Dochez and Avery* raised the question whether the action of 

 pneumococcal immune serum might in some respects be compar- 

 able to Ascoli's " antiblastic immunity " in anthrax. They 

 thought they were able to show that their immune sera did 

 exercise some inhibitory influence on the growth of cultures. For 

 example : — 



But this retarding influence only lasted for a short time; 

 when plates were made after 24 hours, it was found to have been 

 completely overcome. 



They considered that agglutination and thread formation 

 could not be entirely responsible for the temporary inhibition of 

 growth, because " a marked delay in development occurs in 

 " heterologous immune serum in which no agglutination whatever 

 '' takes place and in which thread formation is not more extensive 

 " than in normal serum." Their view was that there had been 



* Journ. Exper. Med. r XXIII, p. 61. 1916. 



