ANTIBODIES 163 



understood of the actual nature of this reaction itself. That lipoids 

 serve a very important purpose in the absorption or fixation of comple- 

 ment in vitro, as is so well demonstrated in Wassermann's reaction for 

 syphilis, is undoubtedly true, but this does not indicate that the anti- 

 body in the blood-serum of syphilitics is in the nature of a true lipoid 

 antibody, and, indeed, investigation on this subject would seem to 

 indicate that it is not. 1 



It will be understood, therefore, that the question of substances other 

 than proteins acting as true antigens must be regarded as an open one, 

 requiring further investigation. The relation of proteins, however, to 

 the production of antibodies has been fully established, and is at present 

 receiving renewed attention through the researches of Vaughan and his 

 coworkers and Abderhalden. As has been stated in a previous chapter, 

 Vaughan regards the protein constituents of bacterial and other cells as 

 the main antigenic principle capable of causing the production of specific 

 proteolytic ferments, which split the new bacterial protein, releasing a 

 toxic product responsible for the symptoms and lesions of the infection. 

 Abderhalden has also demonstrated the presence of proteolytic ferments 

 in the blood-serum after experimental immunization with proteins, and 

 in the serum of pregnant women, due to the antigenic stimulation of 

 syncytial cells, capable of splitting their substrata in vitro into amino- 

 acids and other simple cleavage-products. These investigations serve 

 to show the intimate relation that proteins bear to the problems of 

 infection and immunity, and demonstrate that antibodies may be largely 

 in the nature of ferments, and that immunologic reactions, both in the 

 living tissues and in the test-tube, are largely in the nature of disin- 

 tegrative enzymic processes. 



ANTIBODIES 



The term antibody is used to designate the specific bodies produced by 

 the cells of a host in reaction against an antigen, as an infecting micropara- 

 site and its products or other foreign protein. 



Various kinds of antibodies may be produced by the same antigen 

 and by different antigens. Some neutralize the soluble toxin of the 

 antigen (antitoxin); others agglutinate or precipitate their antigens 

 (agglutinins and precipitins) ; . still others cause complete dissolution of 

 the antigen (hemolysins, bacteriolysins, etc.), and others again may so 

 alter the antigen and lower its resistance as to render it more easily 

 phagocytable by the body-cells (opsonins or bacteriotropins) . 



1 Further discussion on the question of lipoids acting as antigens will be found 

 in Chapter XXVII in a consideration of anaphylactogens. 



