102 IMMUNE SERA 



that the only satisfactory explanation was one based 

 on the views of Ehrlich and Morgenroth. In Fig. 

 10, A II represents schematically a bacterium a 

 with a number of receptors; for there are many 

 reasons for assuming that each bacterium possesses a 

 number of receptors of the same kind. According 

 to the side-chain theory, if we inject this bacterium 

 into an animal an over-production of the corres- 

 ponding group will occur, resulting in a serum 

 which is rich in body b. This body b, however, is 

 not able by itself to injure the bacteria, and a 

 bacterium all of whose receptors are laden with b 

 need not at all be injured in its vitality. Body b 

 normally possesses a peculiar function, namely, 

 to serve as a coupling member or link, and hence it 

 possesses two groups (amboceptor). As has already 

 been discussed, one of these groups fit the receptors 

 of the bacterium on the one hand and the com- 

 plement on the other. When, therefore, to a normal 

 serum which contains suitable complement, we add 

 equivalent amounts of immune serum, the con- 

 dition pictured in A I will result. On adding the 

 corresponding bacterium to this we get the con- 

 dition shown in A II, in which all the bacterial 

 receptors are occupied with immune bodies, or 

 more accurately, with immune bodies which on 

 their part are loaded with bacteriolytic comple- 

 ment c. in the case here presented let us say that 

 it requires the occupation of all of the receptors 



