FIG. 6. THE VARIOUS TYPES OF RECEPTORS ACCORDING TO 



EHRLICH. 



I. Receptors of the First Order. This type is pictured in a. The 



portion e represents the haptophore group, whilst b represents a 

 toxin molecule, which possesses a haptophore group c and a 

 toxophore group d. This represents the union of toxin and 

 antitoxin, or ferment and antiferment, the union between anti- 

 body and the toxin or ferment being direct. 



II. Receptors of the Second Order are pictured in c. Here e represents 



the haptophore group, and d the zymophore group of the 

 receptor, f being the food molecule with which this receptor 

 combines. Such receptors are possessed by agglutinins and 

 precipitins. It is to be noted that the zymophore group is an 

 integral part of the receptor. 



III. Receptors of the Third Order are pictured in III, e being the 



haptophore group and g the complementophile group of the 

 receptor. The complement k possesses a haptophore group h 

 and zymotoxic group z ; whilst y represents the food molecule 

 which has become linked to the receptor. Such receptors are 

 found in haemolysins, bacteriolysins, and other cytolysins, the 

 union with these cellular elements being effected by the ambo- 

 ceptor (a thrust-off receptor of this order). It is to be noted 

 that the digesting body, the complement, is distinct from the 

 receptor, a point in which these receptors therefore differ from 

 those of the preceding order. 



66 



