250 RECEPTORS OP THE THIRD ORDER 



calls it the "amboceptor." He also uses the word "comple- 

 ment" to denote the dissolving substance, giving the idea 

 that it completes the action of dissolving after it has been 

 united to the cell by the amboceptor, thus replacing 

 Buchner's older term "alexin" for the same dissolving body. 



AMBOCEPTORS. 



The theory of formation of amboceptors is similar to that 

 for the formation of the other types of antibodies. The 

 cell introduced contains some substance, probably protein, 

 which acts as a chemical stimulus to some of the body cells 

 provided with proper receptors so that more of these special 

 receptors are produced, and eventually in excess so that they 

 become free in the blood and constitute the free ambocep- 

 tors. It will be noticed that these free receptors differ from 

 either of the two groups already described in that they have 

 two uniting groups, one for the antigen (cell introduced) 

 named cytophil haptophore, the other for the complement, 

 complementophil haptophore. Hence amboceptors are spoken 

 of as receptors of the third order. They have no other func- 

 tion than that of this double combining power. The action 

 which results is due to the third body — the complement. 

 It will be readily seen that complement must possess at 

 least two groups, a combining or haptophore group which 

 unites with the amboceptor, and an active group which is 

 usually called the zymophore or toxophore group. Comple- 

 ments thus resemble either toxins, where the specific cell 

 (antigen) is injured or killed, or enzymes, in case the cell is 

 likewise dissolved. This action again shows the close rela- 

 tion between toxins and enzymes. Complement may lose 

 its active group in the same way that toxin does and becomes 

 then complementoid. Complement is readily destroyed in 

 blood or serum by heating it to 55° to 56° for half an hour, 

 and is also destroyed spontaneously when serum stands for 

 a day or two, less rapidly at low temperature than at room 

 temperature. 



Amboceptors appear to be specific in the same sense that 

 agglutinins are. That is, if a given cell is used to immunize 



