AGGLUTININS 



47 



serum will act also on colon bacilli. On extracting 

 such a serum with typhoid bacilli, all the aggluti- 

 nating power would be lost, that for typhoid bacilli 

 as well as that for colon. On extracting the serum 

 with colon bacilli, we would remove the aggluti- 

 nating power for these bacilli, but leave the specific 

 agglutinating power for typhoid bacilli. If we 

 extracted the serum with a culture suspected to be 

 typhoid bacilli, and found after extraction that 

 the serum no longer agglutinated known typhoid 

 bacilli, we could conclude that the suspected culture 

 was also one of typhoid bacilli. 



Formation of the Agglutinins According to the 

 Side-Chain Theory Receptors of First, Second and 

 Third Order. Ehrlich's theory as outlined in the 

 preceding chapter offers a ready explanation for the 

 development of these bodies. Certain peculiarities 

 of the agglutinins require merely a slight elabora- 

 tion of detail in order to be clearly understood. 

 According to Ehrlich the prime function of the side 

 chains of a cell is to provide for the nutrition of the 

 cell. Obviously the simplest mechanism for this 

 purpose will be a side chain which merely anchors 

 the food molecule, leaving the digestion entirely to 

 the cell proper. This type of receptor suffices for 

 comparatively small molecules such as those of the 

 toxins, for these are, after all, but the products of 

 cellular activity. When the protoplasm of the 

 bacterial cell itself, however, is to serve as food for 

 the animal cell the latter needs more than a mere 



