ANTIBODIES TO PNEUMOCOCCUS 425 



Substances that neutralize the hemotoxin of Pneumococcus have 

 been discovered in specially prepared immune serum, and some evi- 

 dence has been presented that substances capable of inhibiting the 

 action of the poisonous products of Pneumococcus may arise in 

 the immunization of animals with the so-called pneumococcal 

 toxins. 



In a true sense there are no specific bactericidins for pneumo- 

 cocci. The destructive effect on pneumococci of body tissues is ref- 

 erable to a more complex play of biological elements. 



There exist in the normal animal body, and to a much greater 

 degree in the body of immune animals, substances that render pneu- 

 mococci susceptible to the phagocyting action of mobile leucocytes 

 and the fixed body cells. Disregarding the confusion of terms, the 

 opsonins or tropins act on the bacteria and not on the phagocytic 

 cells and it is by means of the intervention of the normal or im- 

 mune opsonins that, under suitable conditions, pneumococci may 

 be destroyed in the test tube or in the body of the infected animal. 



The combined phenomena of agglutination, precipitation, and 

 opsonization are the complement of forces mustered by the animal 

 body for protection against invading pneumococci. The assump- 

 tion is supported by the close correlation found to exist between 

 the various antibodies concerned in antipneumococcal immunity. 

 The specific protective action of immune serum can be strikingly 

 demonstrated in laboratory animals and the type-specificity and 

 the degree of this protective action can be measured by in vitro 

 methods. Through chemical studies, the protective antibodies have 

 been located in the globulin fraction of immune serum and by both 

 chemical and physical manipulations they may be isolated in rela- 

 tively pure form. Recent advances in these technical procedures 

 have made possible actual measurements of the molecular size of 

 pneumococcal antibodies and are leading to a clearer conception of 

 their chemical composition. 



There remains to be explained the significance of the immuno- 

 logical relation of pneumococcal antigens and antibodies to those 



