CHAPTER XVIII 

 CYTOLYSINS 



Amboccptors and Complements 



THE cytolysins include a number of antibodies of considerable diag- 

 nostic and therapeutic importance, for example, the hemolysins and the 

 bacteriolysins. It will be remembered that the various antibodies act 

 differently upon their antigens, and that, according to the side-chain 

 theory, as their antigens become more highly organized, their structure 

 becomes more complicated. For example, the molecule of a soluble 

 toxin may be considered as simple in structure, and accordingly its 

 antibody has been conceived as being likewise simple, and composed of a 

 plain cast-off receptor or side-arm that unites directly with the toxin 

 and neutralizes it without further aid. Antitoxins and antiferments 

 are antibodies of this nature. For more highly organized antigens, 

 however, so simple an antibody will not suffice, and we now find a more 

 complicated antibody, composed of a portion that unites with the anti- 

 gen and another portion, an integral part of the antibody, that exerts a 

 special selective action upon the antigen, and either neutralizes its activ- 

 ity or prepares it for ultimate destruction. To this class of antibodies 

 belong the agglutinins and precipitins, which agglutinate or precipitate 

 their antigens preparatory, in a sense, to their final disintegration. For 

 still more complex antigens nature has provided special ferments, al- 

 ways present in varying proportions in the blood, which, when united 

 with the antigen, cause its disintegration and solution in a manner simi- 

 lar to the process of digestion as it takes place in the intestinal canal. 

 These ferments are, however, powerless unless united with the antigens, 

 and here we find that the antibody serves as the connecting link, bind- 

 iaguantige.il with ferment, which results in a form of digestion and final 

 lysis or solution. The antibody is, therefore, simple in structure, and 

 is composed of two binding or grasping arms one for the antigen and 

 one for a ferment. This interbody, or amboceptor, is specific for the anti- 

 gen, and will act only and specifically with this antigen. It is important 

 to remember that the ferment or complement is not an integral part of 

 the antibody, but is free in the blood-stream; that the antibody is only 

 a connecting link, but preserves its importance by being specific for its 



antigen; that the primary function of this antibody is to unite antigen 



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