156 IMMUNITY. THEORIES OF IMMUNITY 



The toxophore portion of this antibody, therefore, appears to coagulate 

 or precipitate soluble substances, and, accordingly, the antibody is 

 known as a precipitin. As will be pointed out later, various protein 

 substances, such as blood-serum, milk, egg-albumin, etc., may cause the 

 production of specific precipitins. 



Antibodies of the Third Order (Hemolysins, Bacteriolysins, Cyto- 

 toxins). Still more complex molecules of food material require con- 

 version into simpler substances before they may be assimilated by the 

 molecules of the cell. It is essential that they undergo a sort of digestion, 

 and accordingly Ehrlich has conceived that special side-arms or re- 

 ceptors exist for this purpose, these being composed of two grasping 

 portions, or haptophore groups, one for union with the complex food 

 molecule, the second for union with a special, ferment-like substance 

 present in the blood and called complement. The receptor, therefore, 

 acts simply as a connecting link or interbody between food molecule 

 and complement, bringing the two into relation with each other when 

 the food molecule is rendered soluble, i. e., undergoes lysis. 



With highly organized cell material, such as red blood-corpuscles or 

 bacteria, it is found that receptors of this nature bring about their de- 

 struction by lysis by attaching them to a suitable complement. During 

 infections with various bacteria, therefore, we find that numerous anti- 

 bodies are produced. If the bacteria produce soluble toxins, specific 

 antitoxins are produced to counteract the effects of these; other prod- 

 ucts stimulate the production of agglutinins and precipitins ; still other 

 products or the whole cell cause the production of antibodies, which 

 are not in themselves destructive, but which have the specific power of 

 combining with the cell and bringing about its lysis or destruction by 

 bringing it into relation with the ferment-like complement. It is only 

 by means of a special antibody of this nature that a complement may be 

 united with the pathogenic agent, i. e., the complement itself cannot 

 act directly upon the cell, but must be united by means of the antibody. 



Ehrlich has termed an antibody of this nature an amboceptor, or 

 interbody. In structure, amboceptors are believed to possess two com- 

 bining or grasping portions: one, the haptophore or antigenophore 

 group, for union with the cell; the other the complementophile group, 

 for union with a complement (Fig. 42). 



The lysins (bacteriolysins, hemolysins, and other cytolysins) are 

 antibodies of this order. If, for example, the erythrocytes of one animal 

 are injected into an animal of a different species, hemolysins will be pro- 

 duced, the hemolysin being a specific hemolytic amboceptor that will 



