238 INFECTION AND IMMUNITY 



Theoretical Considerations Concerning Agglutinins and Precipitins. 

 We have seen that Ehrlich evolved his theories _of antibody forma- 

 tion from his early views upon the absorption of nutritive substances by 

 the body cells, and we have followed, in more or less detail, the steps of 

 his reasoning as he developed his hypothesis in its application to the 

 antitoxic and the lytic substances. There still remained the agglutinins 

 and precipitins, bodies which because of their individual characteris- 

 tics can be classed neither with the group of antitoxic, nor with that of 

 the lytic substances. These two antibodies, while by no means identical, 

 possess the common characteristics of being more thermostable than the 

 bacteriolytic substances, and of being insusceptible to reactivation by 

 normal serum. It is plain, therefore, that both agglutinating and 

 precipitating reactions take place without the co-operation of comple- 

 ment. The substances which give rise to precipitins and agglutinins, 



Cell used foi immunising 



FIG. 61. EHRLICH'S CONCEPTION OF THE STRUCTURE OF AGGLUTINIXS AND 



PRECIPITINS. 



moreover, are not of the relatively simple soluble character of the toxins. 

 but are intrinsic portions of complex albuminous molecules, comparable 

 to and often identical with the true nutritive substances. For these 

 reasons Ehrlich believes that the cell-receptors for the various substances 

 which give rise to agglutinins and precipitins are neither of the simple 

 structure of the toxin receptor, nor of the double-haptophore nature of 

 the bacteriolytic receptors, but contain a single haptophore group for 

 the anchorage of the ingested material and at the same time a constantly 

 attached zymophore group or ferment by means of which the an- 

 chored substance is transformed preparatory to its absorption by the 

 cell protoplasm. For the sake of clearness, this form of receptor may 

 be compared to a bacteriolytic or hemolytic amboceptor with a per- 

 manently attached and inseparable complement. 



Three forms of receptors, then, are proposed by Ehrlich in explana- 

 tion of all known varieties of antibodies. The first, the simplest side 



