PRECIPITINS 247 



haptophore group. Also if agglutinins or precipitins be 

 heated to the proper temperature they may retain their 

 combining power but cause no agglutination or precipita- 

 tion, i. e., they are converted into agglutinoid or precipi- 

 tinoid respectively after the analogy of toxin and toxoid. 

 Precipitins like agglutinins possess at least two groups — 

 a combining or haptophore group and a precipitating (some- 

 times called zymophore) group. Hence they are somewhat 

 more complex than antitoxins or antienzymes which have 

 a combining group only. For this reason Ehrlich classes 

 agglutinins and precipitins as receptors of the second order. 



